Human impact on large rivers: the influence of groynes of the River Oder on larval assemblages of caddisflies (Trichoptera)

Human impact on large rivers: the influence of groynes of the River Oder on larval assemblages of... Hydrobiologia (2018) 819:177–195 https://doi.org/10.1007/s10750-018-3636-6 PRIMARY R ESEARCH P APER Human impact on large rivers: the influence of groynes of the River Oder on larval assemblages of caddisflies (Trichoptera) . . . Edyta Buczynska Agnieszka Szlauer-Łukaszewska Stanisław Czachorowski Paweł Buczyn ´ ski Received: 17 June 2017 / Revised: 28 April 2018 / Accepted: 30 April 2018 / Published online: 9 May 2018 The Author(s) 2018 Abstract The influence of groynes in large rivers on assemblages. The distribution of Trichoptera was caddisflies has been poorly studied in the literature. governed inter alia by the plant cover and the amount Therefore, we carried out an investigation on the of detritus, and consequently, the food resources. 420-km stretch of the River Oder equipped with Oxygen, nitrates, phosphates and electrolytic conduc- groynes. At 29 stations, we caught caddisflies in four tivity were important as well. Groynes have had habitats: current sites, groyne fields, riverine control positive effects for caddisflies—not only those in the sites without groynes and in the river’s oxbows. We river itself, but also those in its valley. They can found that groyne construction increased species therefore be of significance in river restoration richness, diversity, evenness, and altered the structure (although originally they served other purposes), of functional groups into more diversified and sus- especially with respect to the radically transformed tainable ones compared to the control sites. The ecosystems of large rivers. groyne field fauna is similar to that of natural lentic habitats, but its composition is largely governed by the Keywords Trichoptera  Species assemblages presence of potential colonists in the nearby oxbows. Large river  Groyne fields  Environmental We distinguished three of the river’s caddisfly disturbances Handling editor: Zhengwen Liu E. Buczyn ´ ska (&) Introduction Department of Zoology, Animal Ecology and Wildlife Management, University of Life Sciences, Lublin, Poland Large rivers are aquatic ecosystems that have been e-mail: edyta.buczynska@gmail.com heavily modified by humans and over many centuries. Urbanisation, industry, chemical pollutants, land-use A. Szlauer-Łukaszewska Department of Invertebrate Zoology and Limnology, change, watercourse alterations, canalisation and dam Szczecin University, Szczecin, Poland construction (Malmqvist & Rundle, 2002) limit bio- diversity in rivers and their valleys, reduce water S. Czachorowski retention in river valleys and diminish their self- Department of Ecology and Environmental Protection, University of Warmia and Mazury, Olsztyn, Poland purification capabilities (Coops et al., 2006; Tockner et al., 2009). Some human actions, however, may have P. Buczynski unintentionally reversed the negative effects of regu- Department of Zoology, Maria Curie-Skłodowska lation. They include the construction of groynes University, Lublin, Poland 123 178 Hydrobiologia (2018) 819:177–195 Fig. 1 Examples of groyne distribution in the Oder valley: A groynes of similar length on a straight stretch of the river; B irregularly shaped groynes along one of the river banks; C groynes of different lengths on both banks of a river bend (source: Google Earth maps) (Fig. 1) which are hard hydraulic structures built at water flow and the recreation of meanders are among right angles to a river bank. They are made from a wide the basic techniques for restoring the diversified variety of materials: in recent years, rock and concrete horizontal river regime and its biodiversity (Zelazo have been most often used. The primary aim of these & Popek, 2002). Because of the increasing instream structures is to make the river channel narrower, habitat complexity that positively affects the species interrupt sediment transport by trapping sediments richness and abundance of the macrofauna (e.g. between groynes and protect river banks from erosion. Boyero, 2003; Maza ˜o & Conceic ¸a ˜o Bispo, 2016), we This, in turn, deepens the water in the channel, thereby can expect successful colonisation of caddisfly species prolonging the period for which the river is navigable. with lentic habitat preferences in the groyne fields. Structures of this kind have long been used in many The potential sources of lentic species in a river valley countries. In Poland, groynes have been built on the are oxbows. Those of the Oder are not completely Vistula (Wisła), Warta and Oder (Odra). The Oder, the natural, since the points where they disembogue into object of our study, has the largest number of groynes: the river are furnished with special groynes preventing they were built at regular intervals over a very long their complete cutoff. This retards succession and distance (Rast et al., 2000), creating the largest prevents the disappearance of these water bodies, uniform stretch of river in Poland (40% of the river’s which can be treated as an unintended recompense for length) with altered habitat conditions. the reduction in standing water habitats. Since oxbows The waters between the groynes, known as ‘groyne provide a potential species pool for lentic riverine fields’, are much calmer than those in the mainstream, habitats (Robinson et al., 2002; Sundermann et al., and lentic habitats have regenerated there. The various 2011), we have considered them in our project as stages of biological succession in the groyne fields comparative habitats for the groyne field fauna. encompass the accumulation of rock debris and The presence of groynes has a positive influence, detritus, the growth of submergent and emergent above all, on fish (e.g. Bischoff & Wolter, 2001), and vegetation, and ultimately the appearance and stabil- to a lesser extent on aquatic invertebrates (e.g. Barbosa isation of assemblages of aquatic invertebrates and et al., 2006; Nakano & Nakamura, 2006; Szlauer- vertebrates. These approaches have been used in the Łukaszewska, 2015). However, there are still no data restoration of original river ecosystems, in which the concerning the biological response of different taxo- formation of various types of structures directing the nomic groups of organisms to varied river channel 123 Hydrobiologia (2018) 819:177–195 179 modifications (Horsak et al., 2009), and the biotic third-largest drainage basin and the sixth-greatest flow effects of river restoration on aquatic assemblages are rate of all the rivers entering the Baltic Sea (Scho ¨ ll still poorly understood (Sundermann et al., 2011). et al., 2003). This also applies to caddisflies: there are no The present study investigated the middle and comprehensive data on the influence of groynes on lower reaches of the Oder over a distance of some 0 0 caddisfly assemblages, even though caddisflies are 420 km (Fig. 2) from Uraz (5114 N, 1651 E) to 0 0 among the more important and numerous constituents Ognica (5304 N, 1422 E). Groynes were studied of the river benthos, occupying the largest number of over a distance of 306 km, from Scinawa (5124 N, 0 0 0 trophic and microhabitat niches of all aquatic inver- 1625 E) to Czelin (5244 N, 1423 E); this is 40% of tebrates (Holzenthal et al., 2007). They are, moreover, the Oder’s total length. good indicators of a river’s ecological status (Ce `re `gh- Local hydro-engineering works on the Oder (weir ino et al., 2001) and of water quality (Pirvu & construction) were undertaken as early as the thir- Pacioglu, 2012). The latter aspect is particularly teenth century, but the river was regulated on a large important in the case of the Oder: although its waters scale between 1741 and 1896. As a result, the Oder lost have been placed in biochemical and physical and its meandering character, leaving many oxbows, now chemical classes 2 or 3 (good or satisfactory quality), cut off from the mainstream. Around 10 000 groynes the overall quality of its waters is poor (class 4) were constructed to protect the river banks from resulting from their high nutrient levels (Lewicki, erosion: this shifted the main current to the middle of 2011; WIOS Wrocław, 2012). Identifying assem- the channel, which also improved conditions for blages of Trichoptera, drivers of their distribution, navigation. The groynes are built of stone blocks, assessing their response to transformations and dis- and their tips, which receive the full force of the faster turbances, and understanding their habitat relation- flowing, turbulent waters, are bare. There is usually ships in the ecosystems of large rivers may not only be sand or gravel in the sediment. The sediments in the recognisably important. Most importantly, the knowl- areas between the groynes, known as groyne fields, edge acquired can be applied to the implementation of where the current is not so strong, are sandy or muddy, EU recommendations for biodiversity conservation while those in the inner parts of the groyne fields are and improving the status of waters, contained in the mostly muddy and support marshland vegetation with Natura 2000 programme and the Framework Water dominant Phalaris arundinacea; elodeids are found in Directive. this zone, too. The sediments in the middle, deepest This study examines the following hypotheses: (1) part of the groyne fields are sandy, often with traces of the fauna and functional groups of Trichoptera deoxygenation; this is where big boulders and large resemble those of natural habitats of a similar amounts of shell debris accumulate. The habitat character, (2) groyne constructions secondarily conditions in this area resemble those of the increase the biodiversity of the river and its valley supralittoral. by introducing habitat complexity, (3) both physical Apart from the areas of standing water between the and chemical and structural (hydrodynamic) factors groynes, the other lentic habitats along the stretch of are key to the distribution of caddisfly species in a river the Oder that we investigated are oxbows (length: subjected to human pressure. 520–5000 m; width: 20–630 m). They are usually the remains of former meanders that were cut off as a result of the river’s regulation. Their bottom sediments Materials and methods are sandy and silty with a substantial admixture of organic matter, sometimes forming a layer of sapropel. Study area The littoral zone is dominated by sedges (Carex spp.) with admixtures of other helophytes. Elodeids and The Oder rises in the Oderske vrchy mountains nympheids are also present. When water levels are (eastern Czech Republic) and empties into the high, the terrestrial vegetation by the shore is Szczecin Lagoon, and ultimately the Baltic Sea inundated. (north-western Poland). With its length of 854 km and catchment area of 118 861 km , the Oder has the 123 180 Hydrobiologia (2018) 819:177–195 Fig. 2 Study area. A national boundary, B large rivers, C tributaries, D cities, E sampling stations (orange dots—control sites, green dots—groyne fields, blue dots—current sites, red dots—oxbows) Sampling methods material was gathered by hand with a long-handled net (25 cm square frame, 50 lm mesh). On an even Sample materials were collected at 29 research bottom, the net was dragged for a set distance in order stations (Fig. 2), whereas the groynes themselves to gather up the surface layer of bottom sediments. were investigated at 15 of them (Sites: 3, 5–8, 11, 12, Where the bottom was overgrown or uneven, stony or 14, 16–19, 21, 23, and 24). The groyne site samples very hard, the sample was obtained by sweeping. The were taken from the groyne tips (‘‘current sites’’) at 13 sampling sites were designated in such a way as to stations and from the groyne fields at 14. For include all the microhabitats present at a given station comparison, the fauna of oxbows as natural areas of and to ensure that they all differed distinctly from one standing water was analysed at 12 stations (Sites: 2, 4, another. In general, we collected 186 samples from 7, 9, 10, 13, 15, 17, 20, 22, 25, and 27), while 4 stations sand, 238 from mud, 31 from gravel and 59 from (Sites: 1, 26, 28, and 29) were on stretches of the river rocks. 309 samples were gathered from the sites with without groynes but with reinforced banks (‘‘control plants and 188 from sites without vegetation. sites’’). The mud was rinsed out of the samples in the field Samples of benthos (497 in all) were taken in the in a 50 lm net, while the larger debris was removed on spring, summer and autumn of 2009 and 2010. The a 5 mm mesh sieve (during this procedure 123 Hydrobiologia (2018) 819:177–195 181 macrobenthic organisms were picked out by hand). Curtis formula and Shannon’s index. Hierarchical The mineral fractions were removed from sandy and agglomerative clustering with the Unweighted Pair gravelly sediments by sedimentation. The samples Group Method with Arithmetic Mean (UPGMA) of were then fractionated into macro- and meiobenthos pooling species allowed us to distinguish caddisfly on a 3 mm mesh net. The material was preserved in assemblages in the river based on qualitative similar- 98% ethanol. ity relationships. Non-metric multidimensional scal- The caddisflies were identified to species level ing (NMDS) revealed the relationships between the whenever possible. Identification to a higher taxon sites representing these four habitats based on Bray– (genus or family) was necessary if younger larval Curtis faunistic similarities. We also used NMDS stages were present in the material. Exceptions were (based on a taxa presence/absence matrix) to detect larvae of the genus Hydroptila, all of which are whether there was any potential environmental gradi- impossible to identify to species level, and the genus ent impinging on the caddisfly faunas of the River Anabolia, the individuals of which were either A. Oder and its oxbows and similar riverine habitats in furcata Brauer, 1857 or A. laevis (Zetterstedt, 1840). Europe: a regulated river—the Elbe (Scholz et al., The following parameters were measured at every 2005), two natural rivers—the Bug and its oxbows station: the specific electrolytic conductivity of the (Serafin, 2004), the Neman (Czachorowski, 2004), an water (cond), total dissolved solids (TDS), salinity artificial watercourse linked to the Oder—the Oder– (salin), pH (pH), dissolved oxygen concentration (O ), Spree Canal (Muller et al., 2006), as well as the Odra temperature (temp)—all with a Hach-Lange HQ40d 10 years ago (Scho ¨ ll et al., 2003). NMDS and cluster multi-parameter meter; transparency (trans) was esti- analyses were performed in the PAST 3.15 program mated using a Secchi disc. Water samples were (Hammer et al., 2001). analysed on the sampling day with Slandi LF 300 Functional groups (FG) of caddisflies in relation to portable photometers for the presence of contaminants their current and trophic preferences are given after and sewage. With this instrument, the following Graf et al. (2008), with some modifications taking into parameters were measured: ammonium nitrogen consideration the regional specifics of the caddisfly (NH ), nitrites (NO ), nitrates (NO ), phosphates fauna. Taxa were allocated to four categories, accord- 4 2 3 (PO ) and water hardness (hard). ing to their current speed preferences: limnobionts The following structural factors were determined at (lib)—species inhabiting standing waters only, limno- every station: water depth (depth), littoral width phils (lip)—species usually inhabiting standing (lit_width), type of substrate (rocks, gravel, sand, waters, rarely occurring in slowly flowing waters, detritus) and plant coverage (plants). The substrate limnorheophils (lrp)—species preferring standing composition was estimated visually as the proportion waters but regularly occurring in slowly flowing ones, of each of the following substrate particle size classes: and rheophils (rlp)—species occurring in moderately silt/clay/mud: (\ 0.06 mm diameter), sand (0.06–2), to fast-flowing flowing waters. With regard to feeding gravel ([ 2–64) and rock ([ 64) (Gordon et al., 1992). strategies, six categories were distinguished: algae- The vegetation was classified using Braun-Blanquet piercers (alg-pie), filter feeder-predators (ff-pre), phytosociological records. Table 1 lists the relevant gatherers (gat), predators (pre), shredders (shr) and values (minimum, maximum, mean, standard devia- shredder–predators (shr-pre). tion) of 19 environmental variables relating to the We used the Kruskal–Wallis test with Dunn’s post hoc test to find significant differences between the River Oder, which are examined in the following analysis. densities and taxa richness of Trichoptera in the four habitats as well as in four substratum types. We Data analysis applied the Mann–Whitney U test to detect differences between the densities and taxa richness of caddisflies The material was analysed with respect to species and in sites with or without vegetation in the four habitats. ecological (functional) groups using the following All tests were carried out in the Statistica 10.0. indices: dominance, frequency, evenness—Buzas and program. Gibson’s formula, faunistic similarities: quantita- Multivariate ordination analyses were used to tive—Jaccard’s formula, quantitative—the Bray– determine the environmental parameters responsible 123 182 Hydrobiologia (2018) 819:177–195 Table 1 Environmental variables (physical and chemical and structural) measured and estimated at the study sites on the River Oder NH NO NO O [mg pH PO Cond [lS TDS Temp Hardn Trans Salin 4 2 3 2 4 -1 -1 -1 [mg [mg [mg l ] [mg cm ] [mg [C] [mg l ] [m] [%] -1 -1 -1 -1 -1 l ] l ] l ] l ] l ] Physical and chemical parameters of water Min 0.1 0.009 0.6 5.78 6.74 0.009 520 227 6.7 8.38 0.5 0.28 Max 0.7 0.123 10.36 14.67 9.06 0.98 1540 771 22.8 16.14 1.5 0.78 SD 0.1070 0.0222 2.1136 1.7059 0.5943 0.1491 207.70 100.47 4.3536 1.6937 0.2348 0.1049 Mean 0.26 0.03 6.27 11.00 8.27 0.15 897.56 434.12 14.53 12.46 0.92 0.44 Depth [m] Lit_width [m] Rocks Gravel Sand Detritus Plants Structural factors Min 0.05 1 0 0 0 0 0 Max 2 4 55 55 5 SD 0.4366 0.8308 1.1996 1.0606 1.5536 1.6004 1.3114 Mean 0.54 2.23 3.42 4.37 3.38 3.70 3.68 The designations of the variables are explained in the text Min minimum value, Max maximum value, SD standard deviations for the distribution of caddisfly species in the Oder. (Table 2). The Kruskal–Wallis test showed that the Detrended Correspondence Analysis (DCA) was used differences between densities (P = 0.068) and taxo- first to detect the gradient length and, since the nomic richness (P = 0.45) of these habitats were not gradient was short (\ 3 SD), the linear method— statistically significant. Redundancy Analysis (RDA)—was applied. Two The following taxa were the most frequent across separate analyses were applied to each group of the datasets: Anabolia sp. (21 sites), Hydropsyche environmental factors (Table 1). To test the signifi- guttata Pictet, 1834 (17 sites), Limnephilus flavicornis cance of the variables (P \ 0.05), the forward selec- (Fabricius, 1787; 15 sites), young larval stages of tion procedure was used with the Monte Carlo Limnephilidae and the genus Limnephilus (14 each) permutation test. RDAs were carried out in CANOCO and Oecetis (13). As many as 18 taxa were found at 4.5 for Windows (ter Braak & Smilauer, 2002). only one site. The dominance structure of the entire fauna (Table 2) was very uneven: two taxa were eudominant (Anabolia sp. and early instar Limnephil- Results idae), another two were dominant (early instar Lim- nephilus sp. and Limnephilus flavicornis), seven were A total of 497 hydrobiological samples were collected; subdominant, while as many as 34 were recedent. The caddisflies were present in 212 (42.6%) of them. 1033 quantitative taxonomic structures in the various habi- specimens of Trichoptera representing 45 taxa (33 tats differed. The genus Hydropsyche was the most species) were collected in general (Table 2). Most numerous in the current, making up almost 90% of all were found in the oxbows, with less than half as many taxa there. The groyne fields were dominated by larvae in the groyne fields. The control sites yielded fewer of the genus Anabolia and of Leptocerus tineiformis still, while the smallest number were from the current. Curtis, 1834; the abundance of as many as 25 taxa was The overall density was also the highest in the oxbows, less than 5% there. Dominating the oxbows were somewhat less in the groyne fields; it was 5 times less juveniles of Limnephilidae and the genus Anabolia;as at the control sites than in the oxbows and 7 times less in the groyne fields, there was a high number (26) of in the current. The taxonomic richness of the oxbows species with an abundance of less than 5%. At the and groyne fields was identical with 31 taxa each; 12 control sites larvae of the genera Anabolia and taxa were from the control sites and 7 from the current Limnephilus were the most numerous. Few taxa 123 Hydrobiologia (2018) 819:177–195 183 Table 2 Caddisflies of the River Oder and its oxbows Taxon Codes Stations C Cu GODF DEN 1. Agraylea sexmaculata Agr_sex 7 – – – 0.19 0.1 3.45 4 Curtis, 1834 Anabolia sp. Ana_sp 7–12, 14–18, 20–21, 24–29 65.19 3.95 28.86 15.65 25.07 65.52 5.8 2. Athripsodes aterrimus Ath_ate 22, 27 – – – 1.15 0.58 6.9 4.5 (Stephens, 1836) Athripsodes sp. 15, 22 – – – 1.72 0.87 6.9 13.3 Ceraclea sp. Cer_sp 5 – – 1.34 – 0.39 3.45 16 3. Cyrnus crenaticornis Cyr_cre 15, 17, 20, 25,27 – – 2.35 0.95 1.16 17.24 6.1 (Kolenati, 1859) 4. Cyrnus flavidus McLachlan, Cyr_fla 11, 17, 18, 20 – – 2.35 0.19 0.77 13.79 7.94 Cyrnus sp. 12 – – 0.34 0 0.1 3.45 1.1 5. Ecnomus tenellus Rambur, Ecn_ten 21 – – 0.34 0 0.1 3.45 1.3 6. Glyphotaelius pellucidus Gly_pel 17, 19, 22, 27 – – 0.34 0.95 0.58 13.79 2.75 Retzius, 1783 7. Grammotaulius Gra_nig 9 – – – 0.19 0.1 3.45 2 nigropunctatus (Retzius, 1783) 8. Halesus digitatus (Schrank, Hal_dig 16 0.74 – 0.34 – 0.19 3.45 1.35 1781) Halesus sp. 16 – – 0.34 – 0.1 3.45 0.8 9. Hydropsyche Hyd_bul 3, 6–9, 14, 16 – 21.05 7.72 1.15 4.36 24.14 5.3 bulgaromanorum Malicky, 10. Hydropsyche guttata Pictet, Hyd_gut 5, 6, 8, 9, 11, 12, 14, 6.67 25 4.03 0.19 3.97 51.72 2.7 1834 16–19, 21, 23, 24, 26 11. Hydropsyche ornatula Hyd_orn 9 – – – 0.19 0.1 3.45 2 McLachlan, 1878 Hydropsyche sp. 6, 8, 11, 12, 14, 16, 17, 19, – 43.42 3.02 – 4.07 31.03 9.0 Hydroptila sp. 5–8 – 3.95 3.69 – 1.36 13.79 3.1 12. Ironoquia dubia (Stephens, Iro_dub 7 – – 0.34 – 0.1 3.45 2 1837) 13. Leptocerus tineiformis Lep_tin 10, 12, 14, 17, 23, 26, 27 1.48 – 13.76 0.76 4.55 24.14 25.5 Curtis, 1834 Leptoceridae 9, 10, 13, 15, 20, 23, 26, 27 0.74 – 0.34 1.34 0.87 27.59 2.3 14. Limnephilus affinis Curtis, Lim_aff 13, 16, 19, 21–23, 26–28 2.22 1.32 6.04 3.63 3.97 31.03 6.8 15. Limnephilus auricula Curtis, Lim_aur 27 – – – 0.38 0.19 3.45 2.1 16. Limnephilus binotatus Lim_bin 22 – – – 0.57 0.29 3.45 3.35 Curtis, 1834 17. Limnephilus decipiens Lim_dec 9, 11, 16, 21, 22 – – 1.01 0.38 0.48 17.24 2.2 (Kolenati, 1848) 18. Limnephilus flavicornis Lim_fla 2, 4, 10, 11, 13, 15–18, 21, 0.74 – 6.04 8.21 6 48.28 8.7 (Fabricius, 1787) 22, 25–27 19. Limnephilus fuscicornis Lim_fuc 29 2.22 – – – 0.29 3.45 1.15 Rambur, 1842 123 184 Hydrobiologia (2018) 819:177–195 Table 2 continued Taxon Codes Stations C Cu GODF DEN 20. Limnephilus fuscinervis Lim_fun 21–22 – – 0.34 0.19 0.19 6.9 4.65 (Zetterstedt, 1840) 21. Limnephilus lunatus Curtis, Lim_lun 11, 16 – – 1.01 – 0.29 6.9 2 22. Limnephilus marmoratus Lim_mar 22 – – – 0.95 0.48 3.45 40 Curtis, 1834 23. Limnephilus nigriceps Lim_nig 29 0.74 – – – 0.1 3.45 0.7 (Zetterstedt, 1840) 24. Limnephilus politus Lim_pol 22 – – – 0.76 0.39 3.45 6.65 McLachlan, 1865 25. Limnephilus rhombicus Lim_rho 11 – 1.32 – – 0.1 3.45 12 (Linnaeus, 1758) 26. Limnephilus stigma Curtis, Lim_sti 22 – – – 0.19 0.1 3.45 2.7 27. Limnephilus vittatus Lim_vit 25 – – – 0.19 0.1 3.45 2.9 (Fabricius, 1798) Limnephilus sp. 10, 13, 14, 16, 17, 20–27, 11.11 – 2.35 10.69 7.55 48.28 15.1 Limnephilidae 8–10, 13, 16, 17, 20–27 7.41 – 5.37 36.07 20.81 48.28 23.2 28. Mystacides azurea Mys_azu 8 – – 0.34 – 0.1 3.45 4 (Linnaeus, 1758) Mystacides sp. 9, 17, 25 – – 0.34 3.24 1.74 13.79 4.6 29. Oecetis furva (Rambur, Oec_fur 17, 27 – – 0.34 0.19 0.19 6.9 8.15 1842) 30. Oecetis lacustris (Pictet, Oec_lac 2, 11, 15, 17, 18, 21, 25 – – 2.35 2.67 2.03 24.14 7.2 1834) 31. Oecetis ochracea (Curtis, Oec_och 1, 2, 11, 15, 18, 24, 0.74 – 1.01 0.57 0.68 20.69 13.45 1825) 32. Oecetis testacea (Curtis, Oec_tes 8, 16 – – 0.67 – 0.19 6.9 5.85 1834) Oecetis sp. 2, 6, 9, 10, 12, 15, 17, – – 2.35 6.11 3.78 44.83 12.2 21–25, 27 33. Triaenodes bicolor (Curtis, Tri_bic 16, 17, 21, 22 – – 1.01 0.38 0.48 13.79 2.68 1834) Number of taxa 12 7 31 31 Number of species 8 4 20 24 Number of specimens 135 76 298 524 Mean densities 11 7.3 9.6 9.4 Shannon diversity index 1.31 1.4 2.61 2.26 Eveness index 0.30 0.58 0.43 0.31 C control sites, Cu current sites (groyne tips), G groyne fields, O oxbows, D dominance, F frequency, DEN densities (indiv./m ) occurred in all four habitat types: larvae of Anabolia The quantitative faunistic associations between the sp., Hydropsyche guttata and Limnephilus affinis various sites, classified according to habitat type, are Curtis, 1834. given in the NMDS plot in Fig. 3. The fauna of the 123 Hydrobiologia (2018) 819:177–195 185 Fig. 3 Two-dimensional non-metric multidimensional scaling (NMDS) plot showing the arrangement of the study sites representing four habitat types based on Bray– Curtis faunistic similarities (orange dots—control sites, green dots—groyne fields, blue dots—current sites, red dots—oxbows) current sites is the most homogeneous and different numbers of rheophils were found at the current sites, from most sites. The groyne fields exhibit the greatest whereas limnophils were dominant at the control sites. overlap with the oxbow fauna. Three of the control The percentage abundances of limnobionts, limno- sites (26, 28, and 29) share a similar fauna, being the phils and rheophils were roughly the same in the river least closely associated with the current. Worth itself, but limnophils predominated across the dataset emphasising is the fact that the most oxbow or groyne (river and oxbows). The feeding group structure in the field sites are situated on opposite sides of Coordinate four habitats (Fig. 4b) was highly diversified: the 2, which indicates some differences between these control and current sites featured the lowest number of habitat types. Spatial proximity (e.g. Sites 3, 4, and 5) trophic categories and the overwhelming dominance may be responsible to some extent for the faunistic of one of them: shredder–predators in the former and similarities found between groyne fields and oxbows. filter feeding predators in the latter. The species found In general, the oxbows and groyne fields exhibited the in the groyne fields and oxbows were representative of greatest qualitative faunistic similarity (48%), all the feeding groups, but shredder–predators were whereas the groyne fields and control sites were dominant—51% in the groyne fields and as many as quantitatively the most similar (56%). The caddisfly 76% in the oxbows. Indeed, more than half of all the fauna at current sites displayed the greatest dissimi- river caddisflies were shredder–predators. larity, the level of its similarity with the other three Analysis of species co-occurrence in the dataset habitat types being very low. from the river itself (Fig. 5) yielded three distinct Analysis of functional groups (FG) with respect to assemblages of Trichoptera. Assemblage 1 contained current preferences (Fig. 4a) showed that the propor- species with a preference for lentic habitats: they were tions of species representing the various categories almost exclusively large detritus feeding/predatory displayed the greatest similarity in the case of groyne Limnephilidae. This assemblage could be regarded as fields and oxbows: limnophils and limnobionts were typical of groyne fields, so long as the appropriate dominant in both habitats. The absolutely largest aquatic vegetation was present. Assemblage 2 123 186 Hydrobiologia (2018) 819:177–195 Fig. 4 Percentage (a) contribution of trichopteran functional groups based on a current preferences (lib— limnobionts, lip— limnophils, lrp— limnorheophils, rhp— rheophils) and b food preferences (alg-pie— algae-piercers, ff-pre—filter feeder-predators, gat— gatherers, pre—predators, shr—shredders, shr-pre— shredder–predators) in each Cu habitat (C, Cu, G, O), in the River Oder (R) and at all the stations (T) 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% lib lip lrp rhp (b) Cu 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% alg-pie ff-pre gat pre shr shr-pred consisted of two separate but equivalent subgroups: regarded as an indicator for groyne fields, although one included two species from the genus Hydropsy- its constituent species have never been found at the che, which could be treated as indicators for the groyne tips. The species in assemblages 1 and 3, groyne tips, while the other encompassed limnophilic characteristic of groyne fields, were also found in Anabolia larvae and Limnephilus flavicornis, which oxbows in a ratio of 2:1. inhabited groyne fields and oxbows to an equal extent. Separate redundancy analysis (RDA) of the influ- The character of assemblage 2 was transitional ence of two sets of environmental variables (physical between current-groyne fields and oxbows. Assem- and chemical as well as structural) relating to the river blage 3 comprised limnobionts, mainly predaceous showed that these factors explained to only a small caddisflies from the families Leptoceridae and Poly- degree the overall variability of the river’s caddisflies centropodidae. This assemblage could also be (15.5 and 9%, respectively). In the first analysis 123 Hydrobiologia (2018) 819:177–195 187 Fig. 5 Cladogram showing the caddisfly assemblages of the River Oder based on species co-occurrences (Jaccard’s formula). The taxon codes are given in Table 1 (Fig. 6a), the first axis of the plot was defined by the River Bug oxbows. On the NMDS plot these three temperature and the second by the oxygen content. habitats are combined with rivers of a natural charac- The following of the 12 variables were statistically ter: the Bug and the Neman. The fauna of the Oder significant—in descending order: oxygen content, 10 years ago most resembles the fauna of the Elbe, nitrates, electrolytic conductivity and phosphates. As while the most distinct fauna is that of the Oder–Spree regards membership of the caddisfly assemblages, Canal. These three latter habitats are in opposition to only two of the seven structural parameters of the the remaining habitats against coordinate 2, which study sites (Fig. 6b) were significant: detritus on mud indicates that this dimension may be associated with and plant coverage. The first axis defined the former the degree of habitat transformation. parameter, and the second axis the latter. The situation regarding the substrate is less clear: the vector of the detritus fraction on mud lies close to the gravel Discussion substrate, a non-significant factor, which hinders an unequivocal interpretation of the results. The effects of groynes on the caddisfly fauna Comparison of the species composition of the Oder of a river and its valley and its oxbows with different river systems (both natural and anthropogenically disturbed) as well as a According to Barbosa et al. (2006), hydro-engineering canal in Europe and the Oder itself 10 years ago works interfere with the natural continuity of the river, (Fig. 7) reveals some trends. The fauna of the Oder making it more homogeneous. Groynes were con- and its oxbows is the most similar to the fauna of the structed along the Oder, a river already radically 123 188 Hydrobiologia (2018) 819:177–195 Fig. 6 RDA biplots showing caddisfly taxa in relation to abbreviations of the variables and caddisfly taxa codes are given physical and chemical a and structural b parameters of the in Tables 1 and 2, respectively River Oder (the underlined variables are significant). The transformed: as a result, the number of microhabitats which there is a naturally occurring, distinct pool-riffle increased, thereby enhancing the river’s habitat sequence, clearly favouring a high level of diversity heterogeneity. This, in turn, led to a rise in the among the Trichoptera (Schmera & Eros, 2004; Feio numbers of taxa, varied assemblages, greater biodi- et al., 2005). The presence of groynes increased taxon versity and a diverse structure of functional groups richness almost threefold and species diversity two- among caddisflies. Moreover, the stretch of the Oder fold in relation to the control sites. Moreover, the with its groynes that we studied is evidently associated species composition has been enriched primarily by with the oxbows, thereby relating to natural rivers. species from the families Limnephilidae and Lepto- This may indicate that groynes promote a caddisfly ceridae, typical of standing waters, associated chiefly fauna typical of natural or restored watercourses. After with tall reedbeds, nympheids and elodeids (Wallace, nearly 300 years since the groynes were constructed, 1991). Large rivers generally have a species-rich habitats with characteristic features have formed and trichopteran fauna (van Urk et al., 1991), whereas stabilised in the river, which to a large extent may potamal zones are inhabited by certain species only. perform similar functions to the natural habitats The species richness and composition of larval formerly more prevalent in these systems. Groynes Trichoptera in the Oder is much the same as and may replicate habitats historically created by fallen typical of analogous stretches of other European rivers trees, and in this light they can be regarded as a (van Urk et al., 1991; Uherkovich & No ´ gra ´di, 1995; replacement for large tree trunks and woody debris in Tockner et al., 2009). In the Oder, these factors are an unmodified river system. In parallel, groynes and evidently governed by the presence of groynes: groyne fields can be compared to watercourses in without them, the river’s fauna would be considerably 123 Hydrobiologia (2018) 819:177–195 189 Fig. 7 Two-dimensional non-metric multidimensional scaling (NMDS) of rivers (Oder nowadays and in the past, Bug, Neman, and Elbe), oxbows (in the Oder and Bug valleys) and a canal (Oder–Spree) based on caddisfly taxa composition (the presence–the absence data) poorer. All of the above confirms our second hypoth- caddisfly species and diversity index before and after esis that groynes may support secondarily the caddis- the flood on the River Shinano were relatively fly biodiversity of the river and its valley. In natural constant, which indicates that these insects are well riverine ecosystems, the assemblages we regard as adapted, at least in relation to natural disturbances. being typical of groyne fields occur in lentic habitats, Consequently, they are good indicators of the various which are governed, for example, by the meandering transformations of riverine environments and are of the river. This is confirmed by the results of Nakano useful for the possible monitoring of renaturalisation and Nakamura (2006), who found a similar species processes. composition of invertebrates in a restored meander The colonisation of a river valley by invertebrates and groyne stretch of the River Shibetsu. Again, the can take place over various distances, and its success groyne tips provide suitable habitats for rheophils depends on the dispersal abilities of particular species, (Hydropsychidae), which occurred in small numbers the availability of suitable habitats (microhabitats) and or not at all at the control sites. This means that not the existence of source populations (e.g. Sundermann only groyne fields but also current sites support et al., 2011;Mu ¨ ller-Peddinghaus & Hering, 2013). different specialised fauna, which confirms our first Important habitats enhancing river populations in river and second hypotheses. In spite of factors unfavour- valleys are the various types of waters, including able to invertebrates, both natural (e.g. variations in oxbows (Ward et al., 2002), which are regarded as water level, flooding) and anthropogenic (e.g. pollu- biodiversity ‘‘hot spots’’ (Simon et al., 2013). In the tion, water traffic), a specialised and quite Danube riverscape, for example, dynamically con- stable assemblage of Trichoptera has developed along nected water bodies (channels) were found to be this stretch of the Oder. This is particularly evident in crucial for maintaining the biodiversity of dragonflies the groyne fields which act on the ‘‘inner island’’ (Tockner et al., 1999). The occurrence of particular principle, the taxonomic and functional distinctive- caddisfly species in the Oder groyne fields is to a large ness of which are underscored by our results. extent due to the presence of standing water bodies According to Kimura et al. (2011), the number of (oxbows) nearby. Evidence for this may be the high 123 190 Hydrobiologia (2018) 819:177–195 degree of qualitative similarity (46.5%) between the et al., 2011), a finding that stands in agreement with stretch with groynes and the oxbows; for comparison, our own results. the same index for the control sites and oxbows is 26%. The significant relationships between the faunas Functional groups of caddisflies in the context of the groyne fields and oxbows were also indicated by of the groyne system the NMDS plot as well as the clear distinction of stagnophilous assemblages 1 and 3, which supports Flow dynamics and river stability are generally the first hypothesis of our study. Apart from spatial regarded as the main factors affecting the distribution proximity, the dispersal abilities of some species, of invertebrates in rivers (Jowett, 2003; Wang et al., especially males (Winterbourn et al., 2007), and 2014). Our observations showed that the occurrence upstream/downstream colonisation probably con- pattern of functional caddisfly groups based on river tribute to a high similarity index. The potential effects current preferences is typical and expected: dynamic of temporary water bodies in a river valley are rather eddy shading by groyne tips (Yossef, 2005)is small, as they support a specific assemblage of tolerated by only a few rheophilic species, but the caddisflies with different habitat preferences (Wal- groyne fields, where the current is weaker, are lace, 1991). According to Sundermann et al. (2011), an preferred by limnobionts and limnophils. Similar appropriate species pool in the close vicinity of a river patterns obtained for groyne fields and oxbows also confirm our first hypothesis: not only species compo- is one of the more important preconditions of successful recolonisation and river restoration. The sition but also functional groups reflect close relations numerous oxbows in the Oder valley offer a positive between these habitat types. At groyne tips the fauna is recolonisation potential for the river. Their presence more exposed to hydraulic stress in large rivers and short distance from the mainstream will have because of shipping, a fact emphasised by Brunke shaped the fauna of groyne fields both in the past and at et al. (2002) in the middle Elbe. Fish are a further present. For a river, oxbows are a refuge of many factor limiting species richness at current sites in the species, which, as a result of natural or human-induced Oder: Bischoff & Wolter (2001) showed that young disasters or hydro-engineering measures, for example, rheophilic fish were dominant at groyne tips in may have been eliminated from the mainstream. comparison to other riverine habitats and that they Dispersal of caddisfly species occurs in both the larval were responsible for the significant predatory pressure and imaginal stages and, moreover, operates in both on insect larvae. The stability of a river is governed not directions, i.e. from river to oxbow and vice versa. The only by flow dynamics but also by the type of families Polycentropodidae and Leptoceridae are substrate, sediment transport and, as mentioned ear- dominant among the species common to both habitats: lier, aquatic and riparian vegetation (Rosgen, 1996). this may testify to their greater mobility and eury- All these factors in combination make for a better topicity. On the other hand, the distinctness of oxbows species richness and higher mean densities in groyne is ensured by a large group of Limnephilidae species, fields than in the deeper parts (groyne tips) of the river. which have more specialised habitat requirements. This corresponds with the results of the studies on This would confirm the hypothesis of Mu ¨ ller-Ped- invertebrates in the River Shibetsu with groynes dinghaus & Hering (2013), according to which habitat (Nakano & Nakamura, 2006). All the above factors, specialists among caddisflies are generally weaker and especially the vegetation and shading, also govern dispersers. The biodiversity indices of both the river the trophic structure of invertebrates in a watercourse section with groynes and oxbows are quite high (2.62 (Warner & Hendrix, 1984), although in the case of and 2.26, respectively) in relation to the control sites. large rivers, their importance is regarded as marginal The complex dispersal processes among them and the because of the large volumes of water involved. If, occurrence of as many as 11 taxa exclusive to the however, we bear in mind that caddisflies are limited groyne stretch will tend to increase the biodiversity of to riparian zones, these factors are of significance the whole valley. The diverse species pool in the within groyne fields, as our results have indicated. surroundings will increase the probability of success- Groyne construction has altered the trophic struc- ful recolonisation (Robinson et al., 2002; Sundermann ture of caddisflies: it has become more diversified, even with respect to the proportions of the various 123 Hydrobiologia (2018) 819:177–195 191 trophic categories, especially with reference to the to a large extent modified by human agencies, will be control sites. For comparison, Scholz et al. (2005) also important to this sensitive group of insects. The fact found six functional groups (FG) among the caddis- that most of the RDA variability (ca 76%) remains flies of the middle Elbe, the dominant ones being filter unexplained is quite a common situation in many feeders and predators. In the Oder, we found filter similar studies of macroinvertebrates: this is probably feeder-predators to be the most numerous at the a consequence of the natural complexity and variabil- currents sites, while shredder–predators were the most ity of watercourses (Feio et al., 2005; Ruiz-Garcıa numerous at the control sites and in the groyne fields. et al., 2012). For Trichoptera, the significant structural The presence of numerous filter feeders may be factors turned out to be the vegetation coverage at beneficial as regards improving water quality in a river particular sites and a substrate with detritus. Szlauer- such as the Oder: this was noted by Wetzel et al. Łukaszewska (2015) obtained similar results in the (2014), who studied estuarine ecosystems with groy- same river for ostracods. Buczynski et al. (2017) also nes in Germany. Among all riverine habitats, the found that the vegetation coverage factor was signif- trophic structure of the groyne fields was the most icant for the distribution of dragonflies at the same diversified and similar to the structure of the oxbows. sites studied along the Oder. For Trichoptera, both In this case, too, our first hypothesis has been factors are important in the context of food resources, confirmed. Shredder–predators, consisting mainly of foraging areas, case/net attachment, pupation and protection from predators. Where groynes have been large Limnephilidae, depend on the availability of detritus (Wiggins, 2004) in groyne fields, which is constructed, the groyne fields favour plant develop- derived mainly from the riparian zones, since the ment and detritus deposition. In addition, the presence arboreal vegetation here is rather sparse. According to of groynes in these places stabilises the river, controls Gregory et al. (1991), riparian plant communities offer the adsorption of nutrients and shading, which in turn an abundant and diverse food base for aquatic regulates the water temperature in the littoral zone invertebrates: caddisflies take advantage of this, and (Wang et al., 2014). This again creates favourable groyne fields are colonised by shredder–predator conditions for the functioning of many river verte- species (assemblage 1). Van den Brink et al. (1996), brates and invertebrates. That is why the restoration of who investigated the lower Rhine and Meuse flood- aquatic vegetation in degraded rivers is key to their plains, also found that vegetation was crucial for renaturalisation (Coops et al., 2006; Tockner et al., shredders and predators. According to Rawer-Jost 2009); groynes of the type studied here assist this et al. (2000), shredders and predators are good process. indicators as regards the detection of disturbances Groyne fields thus govern the occurrence of (pollution) in running waters. The distribution of the Trichoptera taxa with definite preferences for plants large group of Limnephilidae was governed by TDS and detritus: both RDA and cluster analysis demon- and conductivity, which may signify this type of strated this. At the same time, at the sample level, the dependence. Classifications based on trophic groups Mann–Whitney U-test showed there to be no signif- are useful for studies of food dynamics, trophic icant differences between sites with or without plants relationships and the evolution of system complexity as regards densities and taxa richness. The same in changing environmental conditions (Gerino et al., results applied to these two indices on the four types of 2003), but the response of organisms from different substrate: the Kruskal–Wallis tests did not reveal any categories is not always unequivocal. differences. In contrast, the total number of taxa in such comparisons is a sensitive metric: there were four Factors influencing Trichoptera in a large river species at only the control sites without plants, but twice as many at such sites with plants. At sites with a Although the physical and chemical together with detritus substrate this index was the highest compared structural parameters explained the variability of with the other types—as many as 26 taxa were found Trichoptera in the Oder’s riverine habitats to only a there (Table 3). Many studies acknowledge that the minimal extent, their significance in particular cases presence of vegetation and detritus increases the was comparable, which confirmed our third research species richness of aquatic invertebrates (e.g. Mu ¨ ller, hypothesis. As we anticipated, both groups of factors, 2002; Schneider & Winemiller, 2008). It is worth 123 192 Hydrobiologia (2018) 819:177–195 Table 3 Metrics of the trichopteran fauna of different types of t_N_i—total number of individuals, H—Shannon’s diversity substrate in the River Oder and its oxbows (m_N_t—mean taxa index, E—evenness) number, m_den—mean density, t_N_t—total number of taxa, Substratum m_N_t m_den t_N_t t_N_i H E River Detritus on mud 2.72 9.95 26 204 2.15 0.33 Sand 2.53 9.37 24 177 2.58 0.55 Gravel 3.38 15.46 10 54 1.80 0.61 Rocks 2.11 5.63 16 74 2.14 0.53 Oxbows Detritus on mud 3.95 13.73 28 328 2.27 0.35 Sand 3.59 8.85 23 183 2.24 0.41 Gravel 1.57 3.24 6 11 1.64 0.86 Rocks 1 3 2 2 0.69 1.00 The highest scores are shown in bold emphasising the fact that the highest mean densities the quality (purity) of the water, are comparable with and number of taxa in the Oder were recorded on a or better than those measured in such rivers as the gravel substrate (Table 3), which at the same time Danube or the Rhine. Among the nutrients—the chief supported the taxonomically poorest fauna, dominated factors lowering Oder water status—only nitrates by Anabolia sp. and Hydropsyche bulgaromanorum exceeded the norm for waters of class I purity during Malicky, 1977. Such ambiguous results (Table 3) may our study (Rozporza ˛dzenie, 2014). The two Hydropsy- be evidence for the disturbing influence of other che species (H. bulgaromanorum and H. guttata) factors at particular sites. Generally speaking, caddis- turned out to be highly resistant to maximum nitrate flies in riverine ecosystems prefer hard (solid) sub- levels which was revealed in the RDA analysis. Many strata (Pliu ¯ raite _ & Kesminas, 2004; Graf et al., 2016). species of this genus are known to be tolerant of In human-disturbed watercourses, certain distribution contaminants, especially organic ones (Pliuraite& _ patterns can be modified: e.g. Ja ¨hnig & Lorenz (2008), Kesminas, 2004; Pirvu & Pacioglu, 2012), and often at in their studies on macroinvertebrates in restored levels far higher than those we measured in the Oder. steams, also found CPOM and coarse gravel important This applies in particular to H. bulgaromanorum for high taxa numbers and abundances. Similarly, (Czachorowski & Serafin, 2004). At the same time, Verdonschot et al. (2016) found cobbles, sand cover both species were associated with low electrolytic and CPOM (Coarse Particulate Organic Matter) conductivity and TDS. Oecetis ochracea (Curtis, related to higher EPT richness and diversity in restored 1825) and Triaenodes bicolor (Curtis, 1834) are and degraded river sections. Our results show that phosphate-sensitive: we found both species in the gravel is important for taxa representing different Oder, but only where phosphate levels were average. functional groups. Both these species were also resistant to low oxygen, Like most other large rivers, the Oder is exposed to the most important factor governing species distribu- contamination as a result of urbanisation as well as tion in the river. Our results concur to a large extent industrial and agricultural practices (Coops et al., with those obtained by Szlauer-Łukaszewska (2014) 2006). Even though the general state of its waters is for ostracods in the Oder: their distribution, too, was described as poor (Lewicki, 2011; WIOS Wrocław, mostly shaped by dissolved oxygen and phosphate 2012), the mean values of the physical and chemical levels. For dragonflies, the most important parameters parameters that we obtained do not deviate signifi- were dissolved oxygen and nitrate levels (Buczyn ´ ski cantly from those measured in other large European et al., 2017). Overall, our results indicate that physical rivers (Tockner et al., 2009). Indeed, the factors and chemical parameters affect variability in caddisfly crucial to the occurrence of caddisflies, like oxygen, assemblages to only a small extent. Nonetheless, since nitrate and phosphate, which are intimately related to some parameters governing the quality (purity) of 123 Hydrobiologia (2018) 819:177–195 193 Czachorowski, S. & E. Serafin, 2004. The distribution and waters are crucial to their occurrence, these insects (or ecology of Hydropsyche bulgaromanorum and Hydropsy- at least certain species) can serve as indicators of che contubernalis (Trichoptera: Hydropsychidae) in eutrophication processes in large rivers. Poland and Belarus. Lauterbornia 50: 85–98. Feio, M. 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Human impact on large rivers: the influence of groynes of the River Oder on larval assemblages of caddisflies (Trichoptera)

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Hydrobiologia (2018) 819:177–195 https://doi.org/10.1007/s10750-018-3636-6 PRIMARY R ESEARCH P APER Human impact on large rivers: the influence of groynes of the River Oder on larval assemblages of caddisflies (Trichoptera) . . . Edyta Buczynska Agnieszka Szlauer-Łukaszewska Stanisław Czachorowski Paweł Buczyn ´ ski Received: 17 June 2017 / Revised: 28 April 2018 / Accepted: 30 April 2018 / Published online: 9 May 2018 The Author(s) 2018 Abstract The influence of groynes in large rivers on assemblages. The distribution of Trichoptera was caddisflies has been poorly studied in the literature. governed inter alia by the plant cover and the amount Therefore, we carried out an investigation on the of detritus, and consequently, the food resources. 420-km stretch of the River Oder equipped with Oxygen, nitrates, phosphates and electrolytic conduc- groynes. At 29 stations, we caught caddisflies in four tivity were important as well. Groynes have had habitats: current sites, groyne fields, riverine control positive effects for caddisflies—not only those in the sites without groynes and in the river’s oxbows. We river itself, but also those in its valley. They can found that groyne construction increased species therefore be of significance in river restoration richness, diversity, evenness, and altered the structure (although originally they served other purposes), of functional groups into more diversified and sus- especially with respect to the radically transformed tainable ones compared to the control sites. The ecosystems of large rivers. groyne field fauna is similar to that of natural lentic habitats, but its composition is largely governed by the Keywords Trichoptera  Species assemblages presence of potential colonists in the nearby oxbows. Large river  Groyne fields  Environmental We distinguished three of the river’s caddisfly disturbances Handling editor: Zhengwen Liu E. Buczyn ´ ska (&) Introduction Department of Zoology, Animal Ecology and Wildlife Management, University of Life Sciences, Lublin, Poland Large rivers are aquatic ecosystems that have been e-mail: edyta.buczynska@gmail.com heavily modified by humans and over many centuries. Urbanisation, industry, chemical pollutants, land-use A. Szlauer-Łukaszewska Department of Invertebrate Zoology and Limnology, change, watercourse alterations, canalisation and dam Szczecin University, Szczecin, Poland construction (Malmqvist & Rundle, 2002) limit bio- diversity in rivers and their valleys, reduce water S. Czachorowski retention in river valleys and diminish their self- Department of Ecology and Environmental Protection, University of Warmia and Mazury, Olsztyn, Poland purification capabilities (Coops et al., 2006; Tockner et al., 2009). Some human actions, however, may have P. Buczynski unintentionally reversed the negative effects of regu- Department of Zoology, Maria Curie-Skłodowska lation. They include the construction of groynes University, Lublin, Poland 123 178 Hydrobiologia (2018) 819:177–195 Fig. 1 Examples of groyne distribution in the Oder valley: A groynes of similar length on a straight stretch of the river; B irregularly shaped groynes along one of the river banks; C groynes of different lengths on both banks of a river bend (source: Google Earth maps) (Fig. 1) which are hard hydraulic structures built at water flow and the recreation of meanders are among right angles to a river bank. They are made from a wide the basic techniques for restoring the diversified variety of materials: in recent years, rock and concrete horizontal river regime and its biodiversity (Zelazo have been most often used. The primary aim of these & Popek, 2002). Because of the increasing instream structures is to make the river channel narrower, habitat complexity that positively affects the species interrupt sediment transport by trapping sediments richness and abundance of the macrofauna (e.g. between groynes and protect river banks from erosion. Boyero, 2003; Maza ˜o & Conceic ¸a ˜o Bispo, 2016), we This, in turn, deepens the water in the channel, thereby can expect successful colonisation of caddisfly species prolonging the period for which the river is navigable. with lentic habitat preferences in the groyne fields. Structures of this kind have long been used in many The potential sources of lentic species in a river valley countries. In Poland, groynes have been built on the are oxbows. Those of the Oder are not completely Vistula (Wisła), Warta and Oder (Odra). The Oder, the natural, since the points where they disembogue into object of our study, has the largest number of groynes: the river are furnished with special groynes preventing they were built at regular intervals over a very long their complete cutoff. This retards succession and distance (Rast et al., 2000), creating the largest prevents the disappearance of these water bodies, uniform stretch of river in Poland (40% of the river’s which can be treated as an unintended recompense for length) with altered habitat conditions. the reduction in standing water habitats. Since oxbows The waters between the groynes, known as ‘groyne provide a potential species pool for lentic riverine fields’, are much calmer than those in the mainstream, habitats (Robinson et al., 2002; Sundermann et al., and lentic habitats have regenerated there. The various 2011), we have considered them in our project as stages of biological succession in the groyne fields comparative habitats for the groyne field fauna. encompass the accumulation of rock debris and The presence of groynes has a positive influence, detritus, the growth of submergent and emergent above all, on fish (e.g. Bischoff & Wolter, 2001), and vegetation, and ultimately the appearance and stabil- to a lesser extent on aquatic invertebrates (e.g. Barbosa isation of assemblages of aquatic invertebrates and et al., 2006; Nakano & Nakamura, 2006; Szlauer- vertebrates. These approaches have been used in the Łukaszewska, 2015). However, there are still no data restoration of original river ecosystems, in which the concerning the biological response of different taxo- formation of various types of structures directing the nomic groups of organisms to varied river channel 123 Hydrobiologia (2018) 819:177–195 179 modifications (Horsak et al., 2009), and the biotic third-largest drainage basin and the sixth-greatest flow effects of river restoration on aquatic assemblages are rate of all the rivers entering the Baltic Sea (Scho ¨ ll still poorly understood (Sundermann et al., 2011). et al., 2003). This also applies to caddisflies: there are no The present study investigated the middle and comprehensive data on the influence of groynes on lower reaches of the Oder over a distance of some 0 0 caddisfly assemblages, even though caddisflies are 420 km (Fig. 2) from Uraz (5114 N, 1651 E) to 0 0 among the more important and numerous constituents Ognica (5304 N, 1422 E). Groynes were studied of the river benthos, occupying the largest number of over a distance of 306 km, from Scinawa (5124 N, 0 0 0 trophic and microhabitat niches of all aquatic inver- 1625 E) to Czelin (5244 N, 1423 E); this is 40% of tebrates (Holzenthal et al., 2007). They are, moreover, the Oder’s total length. good indicators of a river’s ecological status (Ce `re `gh- Local hydro-engineering works on the Oder (weir ino et al., 2001) and of water quality (Pirvu & construction) were undertaken as early as the thir- Pacioglu, 2012). The latter aspect is particularly teenth century, but the river was regulated on a large important in the case of the Oder: although its waters scale between 1741 and 1896. As a result, the Oder lost have been placed in biochemical and physical and its meandering character, leaving many oxbows, now chemical classes 2 or 3 (good or satisfactory quality), cut off from the mainstream. Around 10 000 groynes the overall quality of its waters is poor (class 4) were constructed to protect the river banks from resulting from their high nutrient levels (Lewicki, erosion: this shifted the main current to the middle of 2011; WIOS Wrocław, 2012). Identifying assem- the channel, which also improved conditions for blages of Trichoptera, drivers of their distribution, navigation. The groynes are built of stone blocks, assessing their response to transformations and dis- and their tips, which receive the full force of the faster turbances, and understanding their habitat relation- flowing, turbulent waters, are bare. There is usually ships in the ecosystems of large rivers may not only be sand or gravel in the sediment. The sediments in the recognisably important. Most importantly, the knowl- areas between the groynes, known as groyne fields, edge acquired can be applied to the implementation of where the current is not so strong, are sandy or muddy, EU recommendations for biodiversity conservation while those in the inner parts of the groyne fields are and improving the status of waters, contained in the mostly muddy and support marshland vegetation with Natura 2000 programme and the Framework Water dominant Phalaris arundinacea; elodeids are found in Directive. this zone, too. The sediments in the middle, deepest This study examines the following hypotheses: (1) part of the groyne fields are sandy, often with traces of the fauna and functional groups of Trichoptera deoxygenation; this is where big boulders and large resemble those of natural habitats of a similar amounts of shell debris accumulate. The habitat character, (2) groyne constructions secondarily conditions in this area resemble those of the increase the biodiversity of the river and its valley supralittoral. by introducing habitat complexity, (3) both physical Apart from the areas of standing water between the and chemical and structural (hydrodynamic) factors groynes, the other lentic habitats along the stretch of are key to the distribution of caddisfly species in a river the Oder that we investigated are oxbows (length: subjected to human pressure. 520–5000 m; width: 20–630 m). They are usually the remains of former meanders that were cut off as a result of the river’s regulation. Their bottom sediments Materials and methods are sandy and silty with a substantial admixture of organic matter, sometimes forming a layer of sapropel. Study area The littoral zone is dominated by sedges (Carex spp.) with admixtures of other helophytes. Elodeids and The Oder rises in the Oderske vrchy mountains nympheids are also present. When water levels are (eastern Czech Republic) and empties into the high, the terrestrial vegetation by the shore is Szczecin Lagoon, and ultimately the Baltic Sea inundated. (north-western Poland). With its length of 854 km and catchment area of 118 861 km , the Oder has the 123 180 Hydrobiologia (2018) 819:177–195 Fig. 2 Study area. A national boundary, B large rivers, C tributaries, D cities, E sampling stations (orange dots—control sites, green dots—groyne fields, blue dots—current sites, red dots—oxbows) Sampling methods material was gathered by hand with a long-handled net (25 cm square frame, 50 lm mesh). On an even Sample materials were collected at 29 research bottom, the net was dragged for a set distance in order stations (Fig. 2), whereas the groynes themselves to gather up the surface layer of bottom sediments. were investigated at 15 of them (Sites: 3, 5–8, 11, 12, Where the bottom was overgrown or uneven, stony or 14, 16–19, 21, 23, and 24). The groyne site samples very hard, the sample was obtained by sweeping. The were taken from the groyne tips (‘‘current sites’’) at 13 sampling sites were designated in such a way as to stations and from the groyne fields at 14. For include all the microhabitats present at a given station comparison, the fauna of oxbows as natural areas of and to ensure that they all differed distinctly from one standing water was analysed at 12 stations (Sites: 2, 4, another. In general, we collected 186 samples from 7, 9, 10, 13, 15, 17, 20, 22, 25, and 27), while 4 stations sand, 238 from mud, 31 from gravel and 59 from (Sites: 1, 26, 28, and 29) were on stretches of the river rocks. 309 samples were gathered from the sites with without groynes but with reinforced banks (‘‘control plants and 188 from sites without vegetation. sites’’). The mud was rinsed out of the samples in the field Samples of benthos (497 in all) were taken in the in a 50 lm net, while the larger debris was removed on spring, summer and autumn of 2009 and 2010. The a 5 mm mesh sieve (during this procedure 123 Hydrobiologia (2018) 819:177–195 181 macrobenthic organisms were picked out by hand). Curtis formula and Shannon’s index. Hierarchical The mineral fractions were removed from sandy and agglomerative clustering with the Unweighted Pair gravelly sediments by sedimentation. The samples Group Method with Arithmetic Mean (UPGMA) of were then fractionated into macro- and meiobenthos pooling species allowed us to distinguish caddisfly on a 3 mm mesh net. The material was preserved in assemblages in the river based on qualitative similar- 98% ethanol. ity relationships. Non-metric multidimensional scal- The caddisflies were identified to species level ing (NMDS) revealed the relationships between the whenever possible. Identification to a higher taxon sites representing these four habitats based on Bray– (genus or family) was necessary if younger larval Curtis faunistic similarities. We also used NMDS stages were present in the material. Exceptions were (based on a taxa presence/absence matrix) to detect larvae of the genus Hydroptila, all of which are whether there was any potential environmental gradi- impossible to identify to species level, and the genus ent impinging on the caddisfly faunas of the River Anabolia, the individuals of which were either A. Oder and its oxbows and similar riverine habitats in furcata Brauer, 1857 or A. laevis (Zetterstedt, 1840). Europe: a regulated river—the Elbe (Scholz et al., The following parameters were measured at every 2005), two natural rivers—the Bug and its oxbows station: the specific electrolytic conductivity of the (Serafin, 2004), the Neman (Czachorowski, 2004), an water (cond), total dissolved solids (TDS), salinity artificial watercourse linked to the Oder—the Oder– (salin), pH (pH), dissolved oxygen concentration (O ), Spree Canal (Muller et al., 2006), as well as the Odra temperature (temp)—all with a Hach-Lange HQ40d 10 years ago (Scho ¨ ll et al., 2003). NMDS and cluster multi-parameter meter; transparency (trans) was esti- analyses were performed in the PAST 3.15 program mated using a Secchi disc. Water samples were (Hammer et al., 2001). analysed on the sampling day with Slandi LF 300 Functional groups (FG) of caddisflies in relation to portable photometers for the presence of contaminants their current and trophic preferences are given after and sewage. With this instrument, the following Graf et al. (2008), with some modifications taking into parameters were measured: ammonium nitrogen consideration the regional specifics of the caddisfly (NH ), nitrites (NO ), nitrates (NO ), phosphates fauna. Taxa were allocated to four categories, accord- 4 2 3 (PO ) and water hardness (hard). ing to their current speed preferences: limnobionts The following structural factors were determined at (lib)—species inhabiting standing waters only, limno- every station: water depth (depth), littoral width phils (lip)—species usually inhabiting standing (lit_width), type of substrate (rocks, gravel, sand, waters, rarely occurring in slowly flowing waters, detritus) and plant coverage (plants). The substrate limnorheophils (lrp)—species preferring standing composition was estimated visually as the proportion waters but regularly occurring in slowly flowing ones, of each of the following substrate particle size classes: and rheophils (rlp)—species occurring in moderately silt/clay/mud: (\ 0.06 mm diameter), sand (0.06–2), to fast-flowing flowing waters. With regard to feeding gravel ([ 2–64) and rock ([ 64) (Gordon et al., 1992). strategies, six categories were distinguished: algae- The vegetation was classified using Braun-Blanquet piercers (alg-pie), filter feeder-predators (ff-pre), phytosociological records. Table 1 lists the relevant gatherers (gat), predators (pre), shredders (shr) and values (minimum, maximum, mean, standard devia- shredder–predators (shr-pre). tion) of 19 environmental variables relating to the We used the Kruskal–Wallis test with Dunn’s post hoc test to find significant differences between the River Oder, which are examined in the following analysis. densities and taxa richness of Trichoptera in the four habitats as well as in four substratum types. We Data analysis applied the Mann–Whitney U test to detect differences between the densities and taxa richness of caddisflies The material was analysed with respect to species and in sites with or without vegetation in the four habitats. ecological (functional) groups using the following All tests were carried out in the Statistica 10.0. indices: dominance, frequency, evenness—Buzas and program. Gibson’s formula, faunistic similarities: quantita- Multivariate ordination analyses were used to tive—Jaccard’s formula, quantitative—the Bray– determine the environmental parameters responsible 123 182 Hydrobiologia (2018) 819:177–195 Table 1 Environmental variables (physical and chemical and structural) measured and estimated at the study sites on the River Oder NH NO NO O [mg pH PO Cond [lS TDS Temp Hardn Trans Salin 4 2 3 2 4 -1 -1 -1 [mg [mg [mg l ] [mg cm ] [mg [C] [mg l ] [m] [%] -1 -1 -1 -1 -1 l ] l ] l ] l ] l ] Physical and chemical parameters of water Min 0.1 0.009 0.6 5.78 6.74 0.009 520 227 6.7 8.38 0.5 0.28 Max 0.7 0.123 10.36 14.67 9.06 0.98 1540 771 22.8 16.14 1.5 0.78 SD 0.1070 0.0222 2.1136 1.7059 0.5943 0.1491 207.70 100.47 4.3536 1.6937 0.2348 0.1049 Mean 0.26 0.03 6.27 11.00 8.27 0.15 897.56 434.12 14.53 12.46 0.92 0.44 Depth [m] Lit_width [m] Rocks Gravel Sand Detritus Plants Structural factors Min 0.05 1 0 0 0 0 0 Max 2 4 55 55 5 SD 0.4366 0.8308 1.1996 1.0606 1.5536 1.6004 1.3114 Mean 0.54 2.23 3.42 4.37 3.38 3.70 3.68 The designations of the variables are explained in the text Min minimum value, Max maximum value, SD standard deviations for the distribution of caddisfly species in the Oder. (Table 2). The Kruskal–Wallis test showed that the Detrended Correspondence Analysis (DCA) was used differences between densities (P = 0.068) and taxo- first to detect the gradient length and, since the nomic richness (P = 0.45) of these habitats were not gradient was short (\ 3 SD), the linear method— statistically significant. Redundancy Analysis (RDA)—was applied. Two The following taxa were the most frequent across separate analyses were applied to each group of the datasets: Anabolia sp. (21 sites), Hydropsyche environmental factors (Table 1). To test the signifi- guttata Pictet, 1834 (17 sites), Limnephilus flavicornis cance of the variables (P \ 0.05), the forward selec- (Fabricius, 1787; 15 sites), young larval stages of tion procedure was used with the Monte Carlo Limnephilidae and the genus Limnephilus (14 each) permutation test. RDAs were carried out in CANOCO and Oecetis (13). As many as 18 taxa were found at 4.5 for Windows (ter Braak & Smilauer, 2002). only one site. The dominance structure of the entire fauna (Table 2) was very uneven: two taxa were eudominant (Anabolia sp. and early instar Limnephil- Results idae), another two were dominant (early instar Lim- nephilus sp. and Limnephilus flavicornis), seven were A total of 497 hydrobiological samples were collected; subdominant, while as many as 34 were recedent. The caddisflies were present in 212 (42.6%) of them. 1033 quantitative taxonomic structures in the various habi- specimens of Trichoptera representing 45 taxa (33 tats differed. The genus Hydropsyche was the most species) were collected in general (Table 2). Most numerous in the current, making up almost 90% of all were found in the oxbows, with less than half as many taxa there. The groyne fields were dominated by larvae in the groyne fields. The control sites yielded fewer of the genus Anabolia and of Leptocerus tineiformis still, while the smallest number were from the current. Curtis, 1834; the abundance of as many as 25 taxa was The overall density was also the highest in the oxbows, less than 5% there. Dominating the oxbows were somewhat less in the groyne fields; it was 5 times less juveniles of Limnephilidae and the genus Anabolia;as at the control sites than in the oxbows and 7 times less in the groyne fields, there was a high number (26) of in the current. The taxonomic richness of the oxbows species with an abundance of less than 5%. At the and groyne fields was identical with 31 taxa each; 12 control sites larvae of the genera Anabolia and taxa were from the control sites and 7 from the current Limnephilus were the most numerous. Few taxa 123 Hydrobiologia (2018) 819:177–195 183 Table 2 Caddisflies of the River Oder and its oxbows Taxon Codes Stations C Cu GODF DEN 1. Agraylea sexmaculata Agr_sex 7 – – – 0.19 0.1 3.45 4 Curtis, 1834 Anabolia sp. Ana_sp 7–12, 14–18, 20–21, 24–29 65.19 3.95 28.86 15.65 25.07 65.52 5.8 2. Athripsodes aterrimus Ath_ate 22, 27 – – – 1.15 0.58 6.9 4.5 (Stephens, 1836) Athripsodes sp. 15, 22 – – – 1.72 0.87 6.9 13.3 Ceraclea sp. Cer_sp 5 – – 1.34 – 0.39 3.45 16 3. Cyrnus crenaticornis Cyr_cre 15, 17, 20, 25,27 – – 2.35 0.95 1.16 17.24 6.1 (Kolenati, 1859) 4. Cyrnus flavidus McLachlan, Cyr_fla 11, 17, 18, 20 – – 2.35 0.19 0.77 13.79 7.94 Cyrnus sp. 12 – – 0.34 0 0.1 3.45 1.1 5. Ecnomus tenellus Rambur, Ecn_ten 21 – – 0.34 0 0.1 3.45 1.3 6. Glyphotaelius pellucidus Gly_pel 17, 19, 22, 27 – – 0.34 0.95 0.58 13.79 2.75 Retzius, 1783 7. Grammotaulius Gra_nig 9 – – – 0.19 0.1 3.45 2 nigropunctatus (Retzius, 1783) 8. Halesus digitatus (Schrank, Hal_dig 16 0.74 – 0.34 – 0.19 3.45 1.35 1781) Halesus sp. 16 – – 0.34 – 0.1 3.45 0.8 9. Hydropsyche Hyd_bul 3, 6–9, 14, 16 – 21.05 7.72 1.15 4.36 24.14 5.3 bulgaromanorum Malicky, 10. Hydropsyche guttata Pictet, Hyd_gut 5, 6, 8, 9, 11, 12, 14, 6.67 25 4.03 0.19 3.97 51.72 2.7 1834 16–19, 21, 23, 24, 26 11. Hydropsyche ornatula Hyd_orn 9 – – – 0.19 0.1 3.45 2 McLachlan, 1878 Hydropsyche sp. 6, 8, 11, 12, 14, 16, 17, 19, – 43.42 3.02 – 4.07 31.03 9.0 Hydroptila sp. 5–8 – 3.95 3.69 – 1.36 13.79 3.1 12. Ironoquia dubia (Stephens, Iro_dub 7 – – 0.34 – 0.1 3.45 2 1837) 13. Leptocerus tineiformis Lep_tin 10, 12, 14, 17, 23, 26, 27 1.48 – 13.76 0.76 4.55 24.14 25.5 Curtis, 1834 Leptoceridae 9, 10, 13, 15, 20, 23, 26, 27 0.74 – 0.34 1.34 0.87 27.59 2.3 14. Limnephilus affinis Curtis, Lim_aff 13, 16, 19, 21–23, 26–28 2.22 1.32 6.04 3.63 3.97 31.03 6.8 15. Limnephilus auricula Curtis, Lim_aur 27 – – – 0.38 0.19 3.45 2.1 16. Limnephilus binotatus Lim_bin 22 – – – 0.57 0.29 3.45 3.35 Curtis, 1834 17. Limnephilus decipiens Lim_dec 9, 11, 16, 21, 22 – – 1.01 0.38 0.48 17.24 2.2 (Kolenati, 1848) 18. Limnephilus flavicornis Lim_fla 2, 4, 10, 11, 13, 15–18, 21, 0.74 – 6.04 8.21 6 48.28 8.7 (Fabricius, 1787) 22, 25–27 19. Limnephilus fuscicornis Lim_fuc 29 2.22 – – – 0.29 3.45 1.15 Rambur, 1842 123 184 Hydrobiologia (2018) 819:177–195 Table 2 continued Taxon Codes Stations C Cu GODF DEN 20. Limnephilus fuscinervis Lim_fun 21–22 – – 0.34 0.19 0.19 6.9 4.65 (Zetterstedt, 1840) 21. Limnephilus lunatus Curtis, Lim_lun 11, 16 – – 1.01 – 0.29 6.9 2 22. Limnephilus marmoratus Lim_mar 22 – – – 0.95 0.48 3.45 40 Curtis, 1834 23. Limnephilus nigriceps Lim_nig 29 0.74 – – – 0.1 3.45 0.7 (Zetterstedt, 1840) 24. Limnephilus politus Lim_pol 22 – – – 0.76 0.39 3.45 6.65 McLachlan, 1865 25. Limnephilus rhombicus Lim_rho 11 – 1.32 – – 0.1 3.45 12 (Linnaeus, 1758) 26. Limnephilus stigma Curtis, Lim_sti 22 – – – 0.19 0.1 3.45 2.7 27. Limnephilus vittatus Lim_vit 25 – – – 0.19 0.1 3.45 2.9 (Fabricius, 1798) Limnephilus sp. 10, 13, 14, 16, 17, 20–27, 11.11 – 2.35 10.69 7.55 48.28 15.1 Limnephilidae 8–10, 13, 16, 17, 20–27 7.41 – 5.37 36.07 20.81 48.28 23.2 28. Mystacides azurea Mys_azu 8 – – 0.34 – 0.1 3.45 4 (Linnaeus, 1758) Mystacides sp. 9, 17, 25 – – 0.34 3.24 1.74 13.79 4.6 29. Oecetis furva (Rambur, Oec_fur 17, 27 – – 0.34 0.19 0.19 6.9 8.15 1842) 30. Oecetis lacustris (Pictet, Oec_lac 2, 11, 15, 17, 18, 21, 25 – – 2.35 2.67 2.03 24.14 7.2 1834) 31. Oecetis ochracea (Curtis, Oec_och 1, 2, 11, 15, 18, 24, 0.74 – 1.01 0.57 0.68 20.69 13.45 1825) 32. Oecetis testacea (Curtis, Oec_tes 8, 16 – – 0.67 – 0.19 6.9 5.85 1834) Oecetis sp. 2, 6, 9, 10, 12, 15, 17, – – 2.35 6.11 3.78 44.83 12.2 21–25, 27 33. Triaenodes bicolor (Curtis, Tri_bic 16, 17, 21, 22 – – 1.01 0.38 0.48 13.79 2.68 1834) Number of taxa 12 7 31 31 Number of species 8 4 20 24 Number of specimens 135 76 298 524 Mean densities 11 7.3 9.6 9.4 Shannon diversity index 1.31 1.4 2.61 2.26 Eveness index 0.30 0.58 0.43 0.31 C control sites, Cu current sites (groyne tips), G groyne fields, O oxbows, D dominance, F frequency, DEN densities (indiv./m ) occurred in all four habitat types: larvae of Anabolia The quantitative faunistic associations between the sp., Hydropsyche guttata and Limnephilus affinis various sites, classified according to habitat type, are Curtis, 1834. given in the NMDS plot in Fig. 3. The fauna of the 123 Hydrobiologia (2018) 819:177–195 185 Fig. 3 Two-dimensional non-metric multidimensional scaling (NMDS) plot showing the arrangement of the study sites representing four habitat types based on Bray– Curtis faunistic similarities (orange dots—control sites, green dots—groyne fields, blue dots—current sites, red dots—oxbows) current sites is the most homogeneous and different numbers of rheophils were found at the current sites, from most sites. The groyne fields exhibit the greatest whereas limnophils were dominant at the control sites. overlap with the oxbow fauna. Three of the control The percentage abundances of limnobionts, limno- sites (26, 28, and 29) share a similar fauna, being the phils and rheophils were roughly the same in the river least closely associated with the current. Worth itself, but limnophils predominated across the dataset emphasising is the fact that the most oxbow or groyne (river and oxbows). The feeding group structure in the field sites are situated on opposite sides of Coordinate four habitats (Fig. 4b) was highly diversified: the 2, which indicates some differences between these control and current sites featured the lowest number of habitat types. Spatial proximity (e.g. Sites 3, 4, and 5) trophic categories and the overwhelming dominance may be responsible to some extent for the faunistic of one of them: shredder–predators in the former and similarities found between groyne fields and oxbows. filter feeding predators in the latter. The species found In general, the oxbows and groyne fields exhibited the in the groyne fields and oxbows were representative of greatest qualitative faunistic similarity (48%), all the feeding groups, but shredder–predators were whereas the groyne fields and control sites were dominant—51% in the groyne fields and as many as quantitatively the most similar (56%). The caddisfly 76% in the oxbows. Indeed, more than half of all the fauna at current sites displayed the greatest dissimi- river caddisflies were shredder–predators. larity, the level of its similarity with the other three Analysis of species co-occurrence in the dataset habitat types being very low. from the river itself (Fig. 5) yielded three distinct Analysis of functional groups (FG) with respect to assemblages of Trichoptera. Assemblage 1 contained current preferences (Fig. 4a) showed that the propor- species with a preference for lentic habitats: they were tions of species representing the various categories almost exclusively large detritus feeding/predatory displayed the greatest similarity in the case of groyne Limnephilidae. This assemblage could be regarded as fields and oxbows: limnophils and limnobionts were typical of groyne fields, so long as the appropriate dominant in both habitats. The absolutely largest aquatic vegetation was present. Assemblage 2 123 186 Hydrobiologia (2018) 819:177–195 Fig. 4 Percentage (a) contribution of trichopteran functional groups based on a current preferences (lib— limnobionts, lip— limnophils, lrp— limnorheophils, rhp— rheophils) and b food preferences (alg-pie— algae-piercers, ff-pre—filter feeder-predators, gat— gatherers, pre—predators, shr—shredders, shr-pre— shredder–predators) in each Cu habitat (C, Cu, G, O), in the River Oder (R) and at all the stations (T) 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% lib lip lrp rhp (b) Cu 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% alg-pie ff-pre gat pre shr shr-pred consisted of two separate but equivalent subgroups: regarded as an indicator for groyne fields, although one included two species from the genus Hydropsy- its constituent species have never been found at the che, which could be treated as indicators for the groyne tips. The species in assemblages 1 and 3, groyne tips, while the other encompassed limnophilic characteristic of groyne fields, were also found in Anabolia larvae and Limnephilus flavicornis, which oxbows in a ratio of 2:1. inhabited groyne fields and oxbows to an equal extent. Separate redundancy analysis (RDA) of the influ- The character of assemblage 2 was transitional ence of two sets of environmental variables (physical between current-groyne fields and oxbows. Assem- and chemical as well as structural) relating to the river blage 3 comprised limnobionts, mainly predaceous showed that these factors explained to only a small caddisflies from the families Leptoceridae and Poly- degree the overall variability of the river’s caddisflies centropodidae. This assemblage could also be (15.5 and 9%, respectively). In the first analysis 123 Hydrobiologia (2018) 819:177–195 187 Fig. 5 Cladogram showing the caddisfly assemblages of the River Oder based on species co-occurrences (Jaccard’s formula). The taxon codes are given in Table 1 (Fig. 6a), the first axis of the plot was defined by the River Bug oxbows. On the NMDS plot these three temperature and the second by the oxygen content. habitats are combined with rivers of a natural charac- The following of the 12 variables were statistically ter: the Bug and the Neman. The fauna of the Oder significant—in descending order: oxygen content, 10 years ago most resembles the fauna of the Elbe, nitrates, electrolytic conductivity and phosphates. As while the most distinct fauna is that of the Oder–Spree regards membership of the caddisfly assemblages, Canal. These three latter habitats are in opposition to only two of the seven structural parameters of the the remaining habitats against coordinate 2, which study sites (Fig. 6b) were significant: detritus on mud indicates that this dimension may be associated with and plant coverage. The first axis defined the former the degree of habitat transformation. parameter, and the second axis the latter. The situation regarding the substrate is less clear: the vector of the detritus fraction on mud lies close to the gravel Discussion substrate, a non-significant factor, which hinders an unequivocal interpretation of the results. The effects of groynes on the caddisfly fauna Comparison of the species composition of the Oder of a river and its valley and its oxbows with different river systems (both natural and anthropogenically disturbed) as well as a According to Barbosa et al. (2006), hydro-engineering canal in Europe and the Oder itself 10 years ago works interfere with the natural continuity of the river, (Fig. 7) reveals some trends. The fauna of the Oder making it more homogeneous. Groynes were con- and its oxbows is the most similar to the fauna of the structed along the Oder, a river already radically 123 188 Hydrobiologia (2018) 819:177–195 Fig. 6 RDA biplots showing caddisfly taxa in relation to abbreviations of the variables and caddisfly taxa codes are given physical and chemical a and structural b parameters of the in Tables 1 and 2, respectively River Oder (the underlined variables are significant). The transformed: as a result, the number of microhabitats which there is a naturally occurring, distinct pool-riffle increased, thereby enhancing the river’s habitat sequence, clearly favouring a high level of diversity heterogeneity. This, in turn, led to a rise in the among the Trichoptera (Schmera & Eros, 2004; Feio numbers of taxa, varied assemblages, greater biodi- et al., 2005). The presence of groynes increased taxon versity and a diverse structure of functional groups richness almost threefold and species diversity two- among caddisflies. Moreover, the stretch of the Oder fold in relation to the control sites. Moreover, the with its groynes that we studied is evidently associated species composition has been enriched primarily by with the oxbows, thereby relating to natural rivers. species from the families Limnephilidae and Lepto- This may indicate that groynes promote a caddisfly ceridae, typical of standing waters, associated chiefly fauna typical of natural or restored watercourses. After with tall reedbeds, nympheids and elodeids (Wallace, nearly 300 years since the groynes were constructed, 1991). Large rivers generally have a species-rich habitats with characteristic features have formed and trichopteran fauna (van Urk et al., 1991), whereas stabilised in the river, which to a large extent may potamal zones are inhabited by certain species only. perform similar functions to the natural habitats The species richness and composition of larval formerly more prevalent in these systems. Groynes Trichoptera in the Oder is much the same as and may replicate habitats historically created by fallen typical of analogous stretches of other European rivers trees, and in this light they can be regarded as a (van Urk et al., 1991; Uherkovich & No ´ gra ´di, 1995; replacement for large tree trunks and woody debris in Tockner et al., 2009). In the Oder, these factors are an unmodified river system. In parallel, groynes and evidently governed by the presence of groynes: groyne fields can be compared to watercourses in without them, the river’s fauna would be considerably 123 Hydrobiologia (2018) 819:177–195 189 Fig. 7 Two-dimensional non-metric multidimensional scaling (NMDS) of rivers (Oder nowadays and in the past, Bug, Neman, and Elbe), oxbows (in the Oder and Bug valleys) and a canal (Oder–Spree) based on caddisfly taxa composition (the presence–the absence data) poorer. All of the above confirms our second hypoth- caddisfly species and diversity index before and after esis that groynes may support secondarily the caddis- the flood on the River Shinano were relatively fly biodiversity of the river and its valley. In natural constant, which indicates that these insects are well riverine ecosystems, the assemblages we regard as adapted, at least in relation to natural disturbances. being typical of groyne fields occur in lentic habitats, Consequently, they are good indicators of the various which are governed, for example, by the meandering transformations of riverine environments and are of the river. This is confirmed by the results of Nakano useful for the possible monitoring of renaturalisation and Nakamura (2006), who found a similar species processes. composition of invertebrates in a restored meander The colonisation of a river valley by invertebrates and groyne stretch of the River Shibetsu. Again, the can take place over various distances, and its success groyne tips provide suitable habitats for rheophils depends on the dispersal abilities of particular species, (Hydropsychidae), which occurred in small numbers the availability of suitable habitats (microhabitats) and or not at all at the control sites. This means that not the existence of source populations (e.g. Sundermann only groyne fields but also current sites support et al., 2011;Mu ¨ ller-Peddinghaus & Hering, 2013). different specialised fauna, which confirms our first Important habitats enhancing river populations in river and second hypotheses. In spite of factors unfavour- valleys are the various types of waters, including able to invertebrates, both natural (e.g. variations in oxbows (Ward et al., 2002), which are regarded as water level, flooding) and anthropogenic (e.g. pollu- biodiversity ‘‘hot spots’’ (Simon et al., 2013). In the tion, water traffic), a specialised and quite Danube riverscape, for example, dynamically con- stable assemblage of Trichoptera has developed along nected water bodies (channels) were found to be this stretch of the Oder. This is particularly evident in crucial for maintaining the biodiversity of dragonflies the groyne fields which act on the ‘‘inner island’’ (Tockner et al., 1999). The occurrence of particular principle, the taxonomic and functional distinctive- caddisfly species in the Oder groyne fields is to a large ness of which are underscored by our results. extent due to the presence of standing water bodies According to Kimura et al. (2011), the number of (oxbows) nearby. Evidence for this may be the high 123 190 Hydrobiologia (2018) 819:177–195 degree of qualitative similarity (46.5%) between the et al., 2011), a finding that stands in agreement with stretch with groynes and the oxbows; for comparison, our own results. the same index for the control sites and oxbows is 26%. The significant relationships between the faunas Functional groups of caddisflies in the context of the groyne fields and oxbows were also indicated by of the groyne system the NMDS plot as well as the clear distinction of stagnophilous assemblages 1 and 3, which supports Flow dynamics and river stability are generally the first hypothesis of our study. Apart from spatial regarded as the main factors affecting the distribution proximity, the dispersal abilities of some species, of invertebrates in rivers (Jowett, 2003; Wang et al., especially males (Winterbourn et al., 2007), and 2014). Our observations showed that the occurrence upstream/downstream colonisation probably con- pattern of functional caddisfly groups based on river tribute to a high similarity index. The potential effects current preferences is typical and expected: dynamic of temporary water bodies in a river valley are rather eddy shading by groyne tips (Yossef, 2005)is small, as they support a specific assemblage of tolerated by only a few rheophilic species, but the caddisflies with different habitat preferences (Wal- groyne fields, where the current is weaker, are lace, 1991). According to Sundermann et al. (2011), an preferred by limnobionts and limnophils. Similar appropriate species pool in the close vicinity of a river patterns obtained for groyne fields and oxbows also confirm our first hypothesis: not only species compo- is one of the more important preconditions of successful recolonisation and river restoration. The sition but also functional groups reflect close relations numerous oxbows in the Oder valley offer a positive between these habitat types. At groyne tips the fauna is recolonisation potential for the river. Their presence more exposed to hydraulic stress in large rivers and short distance from the mainstream will have because of shipping, a fact emphasised by Brunke shaped the fauna of groyne fields both in the past and at et al. (2002) in the middle Elbe. Fish are a further present. For a river, oxbows are a refuge of many factor limiting species richness at current sites in the species, which, as a result of natural or human-induced Oder: Bischoff & Wolter (2001) showed that young disasters or hydro-engineering measures, for example, rheophilic fish were dominant at groyne tips in may have been eliminated from the mainstream. comparison to other riverine habitats and that they Dispersal of caddisfly species occurs in both the larval were responsible for the significant predatory pressure and imaginal stages and, moreover, operates in both on insect larvae. The stability of a river is governed not directions, i.e. from river to oxbow and vice versa. The only by flow dynamics but also by the type of families Polycentropodidae and Leptoceridae are substrate, sediment transport and, as mentioned ear- dominant among the species common to both habitats: lier, aquatic and riparian vegetation (Rosgen, 1996). this may testify to their greater mobility and eury- All these factors in combination make for a better topicity. On the other hand, the distinctness of oxbows species richness and higher mean densities in groyne is ensured by a large group of Limnephilidae species, fields than in the deeper parts (groyne tips) of the river. which have more specialised habitat requirements. This corresponds with the results of the studies on This would confirm the hypothesis of Mu ¨ ller-Ped- invertebrates in the River Shibetsu with groynes dinghaus & Hering (2013), according to which habitat (Nakano & Nakamura, 2006). All the above factors, specialists among caddisflies are generally weaker and especially the vegetation and shading, also govern dispersers. The biodiversity indices of both the river the trophic structure of invertebrates in a watercourse section with groynes and oxbows are quite high (2.62 (Warner & Hendrix, 1984), although in the case of and 2.26, respectively) in relation to the control sites. large rivers, their importance is regarded as marginal The complex dispersal processes among them and the because of the large volumes of water involved. If, occurrence of as many as 11 taxa exclusive to the however, we bear in mind that caddisflies are limited groyne stretch will tend to increase the biodiversity of to riparian zones, these factors are of significance the whole valley. The diverse species pool in the within groyne fields, as our results have indicated. surroundings will increase the probability of success- Groyne construction has altered the trophic struc- ful recolonisation (Robinson et al., 2002; Sundermann ture of caddisflies: it has become more diversified, even with respect to the proportions of the various 123 Hydrobiologia (2018) 819:177–195 191 trophic categories, especially with reference to the to a large extent modified by human agencies, will be control sites. For comparison, Scholz et al. (2005) also important to this sensitive group of insects. The fact found six functional groups (FG) among the caddis- that most of the RDA variability (ca 76%) remains flies of the middle Elbe, the dominant ones being filter unexplained is quite a common situation in many feeders and predators. In the Oder, we found filter similar studies of macroinvertebrates: this is probably feeder-predators to be the most numerous at the a consequence of the natural complexity and variabil- currents sites, while shredder–predators were the most ity of watercourses (Feio et al., 2005; Ruiz-Garcıa numerous at the control sites and in the groyne fields. et al., 2012). For Trichoptera, the significant structural The presence of numerous filter feeders may be factors turned out to be the vegetation coverage at beneficial as regards improving water quality in a river particular sites and a substrate with detritus. Szlauer- such as the Oder: this was noted by Wetzel et al. Łukaszewska (2015) obtained similar results in the (2014), who studied estuarine ecosystems with groy- same river for ostracods. Buczynski et al. (2017) also nes in Germany. Among all riverine habitats, the found that the vegetation coverage factor was signif- trophic structure of the groyne fields was the most icant for the distribution of dragonflies at the same diversified and similar to the structure of the oxbows. sites studied along the Oder. For Trichoptera, both In this case, too, our first hypothesis has been factors are important in the context of food resources, confirmed. Shredder–predators, consisting mainly of foraging areas, case/net attachment, pupation and protection from predators. Where groynes have been large Limnephilidae, depend on the availability of detritus (Wiggins, 2004) in groyne fields, which is constructed, the groyne fields favour plant develop- derived mainly from the riparian zones, since the ment and detritus deposition. In addition, the presence arboreal vegetation here is rather sparse. According to of groynes in these places stabilises the river, controls Gregory et al. (1991), riparian plant communities offer the adsorption of nutrients and shading, which in turn an abundant and diverse food base for aquatic regulates the water temperature in the littoral zone invertebrates: caddisflies take advantage of this, and (Wang et al., 2014). This again creates favourable groyne fields are colonised by shredder–predator conditions for the functioning of many river verte- species (assemblage 1). Van den Brink et al. (1996), brates and invertebrates. That is why the restoration of who investigated the lower Rhine and Meuse flood- aquatic vegetation in degraded rivers is key to their plains, also found that vegetation was crucial for renaturalisation (Coops et al., 2006; Tockner et al., shredders and predators. According to Rawer-Jost 2009); groynes of the type studied here assist this et al. (2000), shredders and predators are good process. indicators as regards the detection of disturbances Groyne fields thus govern the occurrence of (pollution) in running waters. The distribution of the Trichoptera taxa with definite preferences for plants large group of Limnephilidae was governed by TDS and detritus: both RDA and cluster analysis demon- and conductivity, which may signify this type of strated this. At the same time, at the sample level, the dependence. Classifications based on trophic groups Mann–Whitney U-test showed there to be no signif- are useful for studies of food dynamics, trophic icant differences between sites with or without plants relationships and the evolution of system complexity as regards densities and taxa richness. The same in changing environmental conditions (Gerino et al., results applied to these two indices on the four types of 2003), but the response of organisms from different substrate: the Kruskal–Wallis tests did not reveal any categories is not always unequivocal. differences. In contrast, the total number of taxa in such comparisons is a sensitive metric: there were four Factors influencing Trichoptera in a large river species at only the control sites without plants, but twice as many at such sites with plants. At sites with a Although the physical and chemical together with detritus substrate this index was the highest compared structural parameters explained the variability of with the other types—as many as 26 taxa were found Trichoptera in the Oder’s riverine habitats to only a there (Table 3). Many studies acknowledge that the minimal extent, their significance in particular cases presence of vegetation and detritus increases the was comparable, which confirmed our third research species richness of aquatic invertebrates (e.g. Mu ¨ ller, hypothesis. As we anticipated, both groups of factors, 2002; Schneider & Winemiller, 2008). It is worth 123 192 Hydrobiologia (2018) 819:177–195 Table 3 Metrics of the trichopteran fauna of different types of t_N_i—total number of individuals, H—Shannon’s diversity substrate in the River Oder and its oxbows (m_N_t—mean taxa index, E—evenness) number, m_den—mean density, t_N_t—total number of taxa, Substratum m_N_t m_den t_N_t t_N_i H E River Detritus on mud 2.72 9.95 26 204 2.15 0.33 Sand 2.53 9.37 24 177 2.58 0.55 Gravel 3.38 15.46 10 54 1.80 0.61 Rocks 2.11 5.63 16 74 2.14 0.53 Oxbows Detritus on mud 3.95 13.73 28 328 2.27 0.35 Sand 3.59 8.85 23 183 2.24 0.41 Gravel 1.57 3.24 6 11 1.64 0.86 Rocks 1 3 2 2 0.69 1.00 The highest scores are shown in bold emphasising the fact that the highest mean densities the quality (purity) of the water, are comparable with and number of taxa in the Oder were recorded on a or better than those measured in such rivers as the gravel substrate (Table 3), which at the same time Danube or the Rhine. Among the nutrients—the chief supported the taxonomically poorest fauna, dominated factors lowering Oder water status—only nitrates by Anabolia sp. and Hydropsyche bulgaromanorum exceeded the norm for waters of class I purity during Malicky, 1977. Such ambiguous results (Table 3) may our study (Rozporza ˛dzenie, 2014). The two Hydropsy- be evidence for the disturbing influence of other che species (H. bulgaromanorum and H. guttata) factors at particular sites. Generally speaking, caddis- turned out to be highly resistant to maximum nitrate flies in riverine ecosystems prefer hard (solid) sub- levels which was revealed in the RDA analysis. Many strata (Pliu ¯ raite _ & Kesminas, 2004; Graf et al., 2016). species of this genus are known to be tolerant of In human-disturbed watercourses, certain distribution contaminants, especially organic ones (Pliuraite& _ patterns can be modified: e.g. Ja ¨hnig & Lorenz (2008), Kesminas, 2004; Pirvu & Pacioglu, 2012), and often at in their studies on macroinvertebrates in restored levels far higher than those we measured in the Oder. steams, also found CPOM and coarse gravel important This applies in particular to H. bulgaromanorum for high taxa numbers and abundances. Similarly, (Czachorowski & Serafin, 2004). At the same time, Verdonschot et al. (2016) found cobbles, sand cover both species were associated with low electrolytic and CPOM (Coarse Particulate Organic Matter) conductivity and TDS. Oecetis ochracea (Curtis, related to higher EPT richness and diversity in restored 1825) and Triaenodes bicolor (Curtis, 1834) are and degraded river sections. Our results show that phosphate-sensitive: we found both species in the gravel is important for taxa representing different Oder, but only where phosphate levels were average. functional groups. Both these species were also resistant to low oxygen, Like most other large rivers, the Oder is exposed to the most important factor governing species distribu- contamination as a result of urbanisation as well as tion in the river. Our results concur to a large extent industrial and agricultural practices (Coops et al., with those obtained by Szlauer-Łukaszewska (2014) 2006). Even though the general state of its waters is for ostracods in the Oder: their distribution, too, was described as poor (Lewicki, 2011; WIOS Wrocław, mostly shaped by dissolved oxygen and phosphate 2012), the mean values of the physical and chemical levels. For dragonflies, the most important parameters parameters that we obtained do not deviate signifi- were dissolved oxygen and nitrate levels (Buczyn ´ ski cantly from those measured in other large European et al., 2017). Overall, our results indicate that physical rivers (Tockner et al., 2009). Indeed, the factors and chemical parameters affect variability in caddisfly crucial to the occurrence of caddisflies, like oxygen, assemblages to only a small extent. Nonetheless, since nitrate and phosphate, which are intimately related to some parameters governing the quality (purity) of 123 Hydrobiologia (2018) 819:177–195 193 Czachorowski, S. & E. Serafin, 2004. The distribution and waters are crucial to their occurrence, these insects (or ecology of Hydropsyche bulgaromanorum and Hydropsy- at least certain species) can serve as indicators of che contubernalis (Trichoptera: Hydropsychidae) in eutrophication processes in large rivers. Poland and Belarus. Lauterbornia 50: 85–98. Feio, M. 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HydrobiologiaSpringer Journals

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