Hydrobiologia

Veyñ, Marianela; Chalde, Tomás; Nardi, Cristina

doi: 10.1007/s10750-026-06143-wpmid: N/A

Environmental DNA (eDNA) based analysis has emerged as a valuable tool for monitoring fish biodiversity, especially in remote and difficult-to-access environments. However, significant knowledge gaps remain regarding the influence of extremely low temperatures and ice cover on eDNA detection in freshwater systems. This study aimed to evaluate the influence of biological and environmental factors on fish detection probability using a species-specific eDNA-based approach in a high-latitude river system. A field experiment was conducted to assess detection of an exotic and a native fish species at two biomass levels and multiple distances from the source across contrasting seasons. Results showed that detection probability was generally higher in summer than in winter. Notably, ice cover had a significant and species-specific impact, drastically reducing detection probability, emphasising the critical role of ice in modulating eDNA persistence and detectability in cold-region freshwater systems. Despite observing an intermittent eDNA signal with no specific spatial pattern over distance, both species were detected at distances up to 640 m from the source, regardless of the biomass and season. These findings underscore the importance of accounting for seasonality when designing eDNA-based protocols and provide guidance for biodiversity monitoring in cold-region freshwater ecosystems facing extreme winters and ice cover.

Veras, Daniel Silas; Ferreira, Maria Fernanda Ribeiro; Lustosa, Guilherme Santana; Castro, Elizete Ribeiro; de Azêvedo, Carlos Augusto Silva; Juen, Leandro

doi: 10.1007/s10750-026-06173-4pmid: N/A

Understanding how local environmental factors and seasonal variation shape aquatic insect communities is key for developing effective biomonitoring tools, especially in ecotonal regions undergoing rapid environmental changes such as the Brazilian Cerrado. In this study, we tested the hypotheses that (1) local environmental variables exert stronger influence than seasonality on EPT composition and (2) environmental gradients define ecological thresholds that affect the abundance and occurrence of sensitive genera, indicating their bioindicator potential. Using redundancy analysis and threshold indicator taxa analysis—TITAN, we found that pH, conductivity, and stream width significantly influenced assemblage composition. TITAN revealed abrupt changes in the abundance of genera such as Guajirolus (Baetidae) and Macrostemum (Hydropsychidae). Although seasonal variation had a smaller effect, it still influenced taxonomic richness. Our results emphasize the importance of local environmental filtering on EPT assemblage structure and suggest that these taxa can be effective indicators of stream habitat integrity, which can be an important tool for monitoring local streams that have currently suffered intense anthropization. We recommend future studies to expand taxonomic resolution, include additional variables such as dissolved oxygen, and consider broader conservation gradients and temporal scales to enhance the detection of robust bioindicator taxa in tropical streams.

Yeo, Hannah H. J.; Ferreira, Laura; Kristensen, Erik; Garm, Anders; Javidpour, Jamileh

doi: 10.1007/s10750-026-06174-3pmid: N/A

Shallow coastal and estuarine habitats are among the most productive ecosystems, sustained by dynamic benthic–pelagic coupling. Yet living-mediated trophic interactions remain underexplored. Here, we present the first field evidence that benthic nereid polychaetes are preyed upon by gelatinous zooplankton: native scyphomedusae Aurelia aurita and invasive ctenophore Mnemiopsis leidyi. These events occurred most frequently in summer, particularly in the inner reaches of a Danish fjord, and were more often associated with A. aurita than M. leidyi. Stable isotope analyses revealed seasonal and species-specific patterns: in summer, polychaetes shared similar isotopic values with their gelatinous predators, while in autumn, they exhibited significant δ15N enrichment, possibly reflecting starvation or decay. Mixing models indicated that polychaetes constitute the second most important dietary component for A. aurita and M. leidyi during summer, after seston or zooplankton, but declined in importance in autumn. These findings uncover an overlooked trophic pathway through which benthic prey subsidise pelagic consumers, strengthening benthic–pelagic coupling. Despite the lower observations in M. leidyi, dietary models suggest ctenophores may exploit this resource opportunistically, with potential implications for competition and invasion dynamics. Our results highlight the need to incorporate benthic–pelagic trophic interactions into ecological models of energy flow and invasion ecology.

Rodriguez-Huezo, Sandra; Ayon-Parente, Manuel; Alonso-Dominguez, Arizbeth; Rodriguez-Zaragoza, Fabian Alejandro; Caceres, Ignacio

doi: 10.1007/s10750-026-06175-2pmid: N/A

Phenotypic plasticity refers to the ability of organisms to adjust traits in response to environmental variation without genetic modification, although this capacity may be constrained in species involved in close ecological associations. This study evaluated whether population traits of the crab Microcassiope xantusii, commonly associated with Pocillopora-dominated reefs, vary according to reef conditions, specifically in relation to coral cover and temperature. Population structure (size and sex distributions, and sex ratio) and population-dynamic traits (growth, mortality, and somatic production) were analyzed across three reefs in the Mexican Central Pacific: Bahía de Chamela (CH), Cuastecomate–Punta Melaque (CT–PM), and Punto B (PB), which differed in habitat condition. Population structure was consistent among reefs, suggesting constraints related to shared habitat characteristics rather than environmental variability. Conversely, population-dynamic traits varied among sites, indicating plastic responses. PB, the warmest reef with the lowest coral cover, exhibited higher individual growth rates, reduced temporal oscillations in growth, and elevated mortality and somatic production. CT–PM showed comparatively low productivity, whereas CH displayed intermediate values across most parameters. Overall, our results suggest that M. xantusii can adjust key population-dynamic traits in response to contrasting reef conditions while maintaining a relatively stable population structure within similar habitat contexts.

da Silva Delgado Mendes, Samuel Lucas; Craveiro, Nykon; de Paiva, Paulo Cesar; Rosa-Filho, José Souto; Nascimento, Rodolfo Leandro

doi: 10.1007/s10750-026-06176-1pmid: N/A

Host structural complexity influences the diversity of associated epifaunal species, but its role in shaping functional trait diversity remains underexplored. We developed a trait-based framework to assess whether macroalgal structural complexity significantly influences the functional assembly of marine annelid epifauna in a sandstone reef system at Enseada dos Corais Beach (NE Brazil). Sampling was conducted in December 2018, February 2019, April 2019, and June 2019. Ten fronds from each of four macroalgal species, Gelidiella acerosa, Palisada perforata (corticated), Padina gymnospora, and Ulva lactuca (foliose), were collected to describe the associated annelid fauna. Structural complexity was quantified using the interstitial space index (ISI), height, and the fractal dimensions of frond area (Da) and perimeter (Dp). Based on body length, feeding strategy, and larval development, the functional trait diversity of annelid assemblages was assessed using Rao’s quadratic entropy (Rao’s Q) and RLQ analysis. Corticated algae species hosted more functionally dissimilar annelid assemblages than foliose ones. Moreover, macroalgal morphological traits influenced epifaunal functional trait composition, particularly during the rainy season, when hydrodynamics are more intense. Our findings thus supported the hypothesis that increased habitat complexity positively influences functional trait diversity in marine macroalgal phytal communities.

Schaeffer, Blake A.; Ferriby, Hannah; Salls, Wilson; Reynolds, Natalie; Hollister, Jeffrey W.; Kreakie, Betty; Shivers, Stephen; Johnson, Brent; Cronin-Golomb, Olivia; Meyers, Kate; Beal, Maxwell

doi: 10.1007/s10750-026-06178-z

Giangreco, Melanie A.; Reisinger, Lindsey S.

doi: 10.1007/s10750-026-06180-5pmid: N/A

Invasive crayfish are common and impactful in freshwater ecosystems. Many invasive species are introduced into reservoirs, and these human-modified ecosystems may alter animals’ behavioral traits and impacts on native species. We collected invasive virile crayfish (Faxonius virilis) and invasive rusty crayfish (Faxonius rusticus) from streams and reservoirs in Vermont, USA, recorded injury rates, and conducted on-site behavioral assays to measure boldness and exploratory behavior. We wanted to know if habitat type was associated with behaviors that could influence crayfish invasion success or impacts on native species. Our findings did not indicate that behavior was influenced by habitat type (e.g., stream or reservoir), but did indicate behavioral differences across sites and correlations between boldness and exploratory behavior in individual crayfish. We found that injury rates were significantly higher in streams than in reservoirs, and that the types of injuries observed were consistent with those expected as a result of aggressive interactions. These findings support previous research on behavioral syndromes (correlated behaviors) in crayfish and raise questions regarding the drivers of intraspecific variation in crayfish behavior and how behavior influences invasive crayfish dispersal and impacts on native species.

Hundermark, Emma; Stoudt, Sara; Takahashi, Mizuki

doi: 10.1007/s10750-026-06186-zpmid: N/A

Environmental DNA (eDNA) analysis is a powerful tool for monitoring wildlife populations. While seasonal peaks in eDNA concentration during breeding seasons of target aquatic species are well documented, fine-scale temporal changes in eDNA are yet to be extensively examined. We used C. a. alleganiensis, an aquatic salamander whose breeding season is characterized by high eDNA concentrations, as a model species to test three hypotheses: eDNA concentration would remain high throughout the expected breeding season, eDNA signatures would reflect synchronous breeding among local populations, and eDNA concentration changes would correspond to seasonal stream-temperature changes. We sampled five tributaries of the Susquehanna River in Pennsylvania, USA, daily from August to October to examine how eDNA concentrations associated with breeding activities changed. We found eDNA concentrations were highly variable within and across sites, but four of the five tributaries showed a predicted eDNA concentration peak in the middle of the sampling period. Temporal changes in eDNA concentrations were site-specific and asynchronous among sites. Despite notable variation across sites, water temperature and its quadratic term were significant predictors of eDNA profiles. Our results revealed the importance of a careful spatiotemporal sampling design for eDNA characterization of breeding seasons in aquatic organisms.

Gorbarán, Rocío; Mac Donagh, María Elicia; Torremorell, Ana

doi: 10.1007/s10750-026-06182-3pmid: N/A

This study aimed to elucidate the relationships between phytobenthos and natural environmental gradients in the least disturbed stream reaches of the Pampean plain. We hypothesized that if basal conditions are maintained, variables associated with the latitudinal gradient, such as irradiance and temperature, should be the main drivers of phytobenthos and that functional trait-based approaches would be more suitable than taxonomic ones for describing these relationships. Eighteen stream reaches belonging to different hydrological basins were selected, based on expected morphological and hydrological characteristics for undisturbed plain streams, with lowest impact from land uses in the surroundings. Traditional taxonomic approach and two functional perspectives based on species traits were used to analyse the responses of phytobenthos to environmental variables of local and regional variability. Due to the favourable conditions given by nutrient availability and low current velocity, we consider and verify through several constrained multivariate analyses, that the natural gradient of temperature and irradiance is one of the main structuring factors of the phytobenthos community. Both taxonomic and functional approaches provided explanations of different aspects of the ecosystem. These results provide a reference baseline to restoration and management policies at a global level, particularly in temperate grasslands ecosystems facing significant anthropogenic pressures.

Merk, Benedikt; Larsen, Martin H.; Baktoft, Henrik; Schnedler-Meyer, Nicolas Azaña; Skov, Christian

doi: 10.1007/s10750-026-06189-wpmid: N/A

Biomanipulation via removal of benthivorous and zooplanktivorous fish is a common method for restoring eutrophic lakes. By affecting zooplankton and nutrient resuspension, these fish increase algal biomass and reduce water clarity. Seine netting is widely used for fish removal, but its efficiency requires further assessment, particularly in relation to the target species’ behaviour. This study examines roach (Rutilus rutilus), a prevalent zooplanktivorous fish in European lakes, aiming to (1) estimate seine net efficiency by assessing overall removal efficiency and specific haul efficiency based on the spatial–temporal overlap between individual fish and net trajectories in small shallow lakes and (2) assess the behaviour of acoustically tagged adult roach at varying population densities to optimize removal timing and locations. Results showed a high overall removal efficiency (93.3%) across 23 hauls, a high specific haul efficiency of 88.8% ± 28.8%, and an overall low escape rate of 6.4%. Roach exhibited seasonal and diurnal aggregation patterns, dispersing in littoral zones during spawning, but forming dense pelagic aggregations in autumn mornings, especially at low densities. This period therefore appears optimal for cost-effective and repeated removal efforts. Further studies across different lake systems are necessary to generalize findings on roach aggregation and seine net efficiency.