Phyto- and zooplankton of the southeastern Barents Sea in April 2000

Spring bloom of cold-water centric and pennate diatoms was observed in two different areas of the southeastern Barents Sea in April 2000: ice-free waters off the Kolguev Island northern shelf and the eastern Pechora Sea near the Karskie Vorota (Kara Gate) Straight in polynyas and ice-free patches in one-year-old ice. Maximal values of phytoplankton abundance and biomass were found at the ice edge. The bloom was localized in shallow water areas with depths less than 50 m in mixing zones of waters of different origin: warm Atlantic, cold coastal, and Arctic (Litke current) waters. Ice melting was among factors inducing the phytoplankton bloom. Each area had a specific phytocoenosis, whose structure was determined by water origin and ice conditions. In the western Kara Sea, under a solid (up to 30 cm thick) ice cover (i.e., under conditions of a hydrological winter), a spring phytoplankton succession was observed from its initial stage. In areas located close to the ice-cover edge, simultaneously with the mass phytoplankton bloom, the early spring zoocoenosis development manifested itself in mass spawning of euphausiids and mass appearance of Cirripedia nauplii and bottom polychaete larvae.

Stable Isotope composition of particulate organic matter and fauna in a deep Mediterranean cold-water coral bank

Cold-water corals (CWC) are frequently reported from deep sites with locally accelerated currents that enhance seabed food particle supply. Moreover, zooplankton likely account for ecologically important prey items, but their contribution to CWC diet remains unquantified. We investigated the benthic food web structure of the recently discovered Santa Maria di Leuca (SML) CWC province (300 to 1100 m depth) located in the oligotrophic northern Ionian Sea. We analyzed stable isotopes (delta13C and delta15N) of the main consumers (including ubiquitous CWC species) exhibiting different feeding strategies, zooplankton, suspended particulate organic matter (POM) and sedimented organic matter (SOM). Zooplankton and POM were collected 3 m above the coral colonies in order to assess their relative contributions to CWC diet. The delta15N of the scleractinians Desmophyllum dianthus, Madrepora oculata and Lophelia pertusa and the gorgonian Paramuricea cf. macrospinawere consistent with a diet mainly composed of zooplankton. The antipatharian Leiopathes glaberrima was more 15N- depletedthan other cnidarians, suggesting a lower contribution of zooplankton to its diet. Our delta13C data clearly indicate that the benthic food web of SML is exclusively fuelled by carbon of phytoplanktonic origin. Nevertheless, consumers feeding at the water sediment interface were more 13C-enriched than consumers feeding above the bottom (i.e. living corals and their epifauna). This pattern suggests that carbon is assimilated via 2 trophic pathways: relatively fresh phytoplanktonic production for 13C-depleted consumers and more decayed organic matter for 13C-enriched consumers. When the delta13C values of consumers were corrected for the influence of lipids (which are significantly 13C-depleted relative to other tissue components), our conclusions remained unchanged, except in the case of L. glaberrima which could assimilate a mixture of zooplankton and resuspended decayed organic matter.