Composition and structure of plankton communities in the Bering Sea

On the data of long-term surveys, mean biomass of plankton in the epipelagic layer of the Bering Sea is evaluated as 821.3 mg/m3 (1058.2 mg/m3 in shelf areas and 760.6 mg/m3 in the deep-water areas) and the stock as 245.1•106 t WW (64.4 • 106 t over the shelf and 180.7 • 106 t in the deep-water sea). By taxa, the average annual portions are: 55.1 % for copepods, 26.3 % for arrowworms, 10.8 % for euphausiids, 3.2 % for medusas, and 2.9 % for amphipods. The dominant species are the arrowworm Sagitta elegans (26.3 %) and the copepod Eucalanus bungii (19.7 %); other mass species are: large-sized copepods Neocalanus cristatus (10.4 %), Neocalanus plumchrus + Neocalanus flemingeri (7.8 %) and Calanus glacialis + Calanus marshallae (5.1 %), euphausiids Thysanoessa raschii (3.5 %) and Thysanoessa longipes (3.4 %), small-sized copepods Metridia pacifica (3.5 %) and Oithona similis (3.5 %), medusa Aglantha digitale (3.2 %).

Mesozooplankton grazing in the coastal Gulf of Alaska: Neocalanus spp. vs. other mesozooplankton

Liu, H., Dagg, J. M., Napp, J. M., and Sato, R. 2008. Mesozooplankton grazing in the coastal Gulf of Alaska: Neocalanus spp. vs. other mesozooplankton. – ICES Journal of Marine Science, 65: 351–360. Three species of large calanoid copepod, Neocalanus flemingeri, Neocalanus plumchrus, and Neocalanus cristatus, dominate the spring biomass of mesozooplankton in the Subarctic Pacific. We compared the grazing impact of Neocalanus species on phytoplankton with grazing by the remainder of the mesozooplankton community in the coastal and shelf waters of the Gulf of Alaska during spring and summer 2003. Neocalanus spp. and other mesozooplankton fed mainly on particles >20 µm, and phytoplankton in the smaller size-fractions (<20 µm) increased in the presence of mesozooplankton, possibly because of a trophic cascade resulting from mesozooplankton consumption of microzooplankton. Neocalanus spp. accounted for most of the mesozooplankton biomass and herbivory in the shelf water of the Gulf of Alaska and in the Prince William Sound (PWS) during April/May. The biomass of other mesozooplankton (mostly small copepods) varied seasonally and spatially; it did not increase in summer after the descent of Neocalanus spp. from the surface layer. On the basis of the clearance rates obtained from our experiments, in spring, grazing by Neocalanus spp. and the remaining mesozooplankton consumed ∼10% of daily growth of phytoplankton >20 µm in the outer-shelf region, where chlorophyll a concentrations were <0.5 mg m−3, and in PWS. Mesozooplankton consumed a smaller percentage of the >20 µm daily phytoplankton production in the inner- and mid-shelf regions where chlorophyll a concentrations were typically >5 mg m−3 with blooms of large diatoms. In summer, without Neocalanus spp. in the surface layer, mesozooplankton grazing accounted for a very small proportion of phytoplankton production across the whole shelf.