ICES Journal of Marine Science: Journal du Conseil

Reeve, Michael R.; Skjoldal, Hein Rune; Harris, Roger

doi: 10.1016/1054-3139(95)80041-7pmid: N/A

Harris, Roger

doi: 10.1016/1054-3139(95)80042-5pmid: N/A

Banse,, Karl

doi: 10.1016/1054-3139(95)80043-3pmid: N/A

Holliday, D. V.; Pieper, R. E.

doi: 10.1016/1054-3139(95)80044-1pmid: N/A

High-frequency acoustical technology is used to measure the spatial distributions of small zooplankton with meter-scale resolution in the vertical, resolutions of hundreds of meters or better in the horizontal, and with temporal resolutions of minutes. Both size and abundance measurements can be made by using sensors in a cast mode from a ship, from undulating towed bodies and by placing instruments on moorings. This presentation includes an overview of some of the technical concepts that are involved, examples of the use of the sensors and systems that have been developed and brief discussions related to the algorithms used to convert acoustical measures to biologically relevant estimates for small zooplankton.

Kleppel, G. S.; Burkart, C. A.

doi: 10.1016/1054-3139(95)80045-Xpmid: N/A

The hypotheses that (1) the egg production (EP) of Acartia tonsa is enhanced by dietary diversity because, (2) dietary diversity increases the probability that a nutritionally complete diet will be obtained, were tested. A. tonsa was provided with a diatom, an approximately equivalent sized dinoflagellate, and a mixture of the two foods. EP, hatching success (H) and gross egg production efficiency varied as diatom < dinoflagellate < mixture. EP and H were then measured with diets consisting of Isochrysis galbana ( = Iso, an alga), or Debariomyces hanseni ( = Deb, a yeast), or Oxyrrhis marina (a heterotrophic dinoflagellate) cultured on either Iso or Deb. EP and H were also determined when each kind of O. marina culture was supplemented with Iso. Fatty acid and amino acid analyses indicated that the two O. marina cultures represented two nutritionally different food items. EP in the Iso, Deb and Iso-fed Oxyrrhis groups was low. In Deb-fed Oxyrrhis and Iso-supplemented groups, EP was high. H was > 60% in Iso-supplemented, yeast-fed O. marina group and < 30% in all others.

Bergeron, Jean-Pierre

doi: 10.1016/1054-3139(95)80046-8pmid: N/A

One method for assessing mesozooplankton production is based on measurements of the activity of an enzyme, aspartate transcarbamylase (ATC), in samples of the whole mesozooplankton community. The first field experiments were carried out in neriti areas, the south-western part of the English Channel and the west of Brittany. Previously published results have shown two main characteristics of ATC activity variations, i.e. an allometric relationship with biomass and a close correlation with the mesoscale changes with time of the mesozooplankton biomass. Other experiments were performed in two oceanic areas, the Ligurian Sea and the upwelling system off the southern coast of Portugal. They illustrated strongly different patterns of ATC activity variations. In the Ligurian Sea, it has not been possible to establish any allometric relationship, probably owing to either fairly complex hydrodynamics or disturbance of the mesozooplankton system caused by an unusual biotic environment. Off Portugal, however, allometric relationships clearly characterized two subsystems, one quite close to the shore and the other in offshore stratified oceanic waters. These results give an overview of different patterns of ATC activity variations in natural systems: some early hypotheses are confirmed, limits in applicability of the method are highlighted and promising prospects are becoming clearer.

Hay, Steve

doi: 10.1016/1054-3139(95)80047-6pmid: N/A

Estimates of copepod secondary production, derived from field estimates of egg production by incubated females and sampled population biomasses, are presented for a range of common North Sea species. Results obtained from a number of cruises, at a variety of times of year and mainly in the northern North Sea, are considered in relation to measured environmental conditions. The large variations in egg production rates found in these field studies frequently do not correlate with temperatures or with chlorophyll as a measure of available food. It is evident that the relations between primary and secondary production are not simple, but rather are complicated by factors such as copepod omnivory and selective feeding.

Kattner, G.; Hagen, W.

doi: 10.1016/1054-3139(95)80048-4pmid: N/A

Herbivorous copepods, especially from polar regions, buffer the pronounced seasonality of primary production through the accumulation of large energy reserves that are deposited as neutral lipids, mainly wax esters but also triacylglycerols. Principal components of these lipids are the long-chain monounsaturated fatty acids and alcohols 20:1(n−9) and 22:1(n−11). Wax ester synthesis based on these compounds is most pronounced in the Arctic copepod, Calanus hyperboreus, but it is also characteristic of the other dominant herbivores, Calanus glacialis and Calanus finmarchicus, as well as for the Antarctic Calanoides acutus. Rhincalanus gigas, another Antarctic species, also fits this scheme of wax ester synthesizers, although its wax esters consist of shorter-chain fatty acids and alcohols. In contrast, the Antarctic Calanus propinguus synthesizes triacylglycerols dominated by the two monounsaturated fatty acid isomers 22: 1(n−11) and 22: 1(n−9). This further elongation of the fatty acids increases their calorific value and may at least partially compensate this species' apparent inability to produce wax esters. Other dominant fatty acids in the lipids of these copepods originate from dietary input and may be used as trophic markers for herbivorous feeding.

Landry, M. R.; Peterson, W. K.; Lorenzen, C. J.

doi: 10.1016/1054-3139(95)80049-2pmid: N/A

Chlorophyll tracer methods were used on six cruises in the Southern California Bight to assess mesozooplankton grazing rates (gut fluorescence), fecal pellet export from the euphotic zone (pigment flux to sediment traps), the partitioning of grazing impact between micro- and mesozooplankton (pigment budget), and phytoplankton growth. Mesozooplankton grazing estimates ranged from 16 to 44% of phytoplankton growth rates during the six cruises, with the mean seasonal average for the spring cruises about double (39%) that from the autumn cruises (20%). Only 23 to 32% of the measured mesozooplankton grazing on phytoplankton was lost rapidly enough from the euphotic zone to be recovered as phaeopigment flux into sediment traps. Since most (68 to 77%) of the grazing activity of mesozooplankton, as inferred from the gut pigment method, does not settle rapidly out of the euphotic zone, it is functionally equivalent (i.e. remineralized within the euphotic zone) to that of microzooplankton as defined by the pigment budget method. The gut fluorescence estimates of mesozooplankton grazing were about equal generally to the sum of micro- and mesozooplankton grazing as inferred from the pigment budget model. Moreover, estimates of phytoplankton growth from the pigment budget were consistently low by a factor of 3 and 4 compared with rates inferred from 14C estimates of production and an assumed C : Chl ratio of 50. Previous studies in systems dominated by large pellet-producing metazooplankton and/or direct cell sinking of phytoplankton have demonstrated that the combined pigment budget estimates of phytoplankton losses were consistent with independent estimates of phytoplankton growth. The lack of such agreement in the present study suggests that the approach may not account adequately for the grazing of protistan microzooplankton.

Nejstgaard, J. C.; Båmstedt, U.; Bagøien, E.; Solberg, P. T.

doi: 10.1016/1054-3139(95)80050-6pmid: N/A

The copepod Calanus finmarchicus was used to quantify effects on the grazing rate due to prey algae characteristics. Laboratory cultures of the haptophytes Emiliania huxleyi, Prymnesium patelliferum, and Pavlova lutheri, the diatoms Thalassiosira nordenskioeldii, T. anguste-lineata, and Chaetoceros calcitrans f. pumidus, and the cryptophyte Rhodomonas baltica were used as food. There was no significant difference in clearance rate between exponential and stationary cultures. Feeding rate increased rapidly with cell diameter (ESD) of the algae in the size range 7–17 μm, while there was no apparent relationship for algae between 3 and 7 μm. E. huxleyi was a suboptimal food with low clearance rates (0–1.6 ml cop−1 h−1) and estimated maximum daily food: body carbon ratios (18%). Feeding rate was not affected by variation in coccolith coverage of the cells. In contrast to the diatoms, there was a pronounced seasonal shift in feeding rate on E. huxleyi. The highest grazing rates coincided with the maximum abundance of E. huxleyi (May-June), and may be caused by seasonal adaptation of the copepod. The feeding on P. patelliferum was lower (0–1 ml cop−1 h−1) than expected from its cell size, and decreased further during incubations > 24 h. A hepatocytic cell test demonstrated a high toxicity of the P. patelliferum strain, although the vitality of C. finmarchicus was not influenced during a two-day exposure in dense suspensions (106 cells ml−1). Thus sublethal toxicity may protect P. patelliferum from copepod predation, being a competitive advantage compared with non-toxic algae.