Mesozooplankton in the Arctic Ocean in summer

The biomass, species and chemical composition of the mesozooplankton and th eir impact on lower food levels were estimated along a transect across the Arctic Ocean. Mesozooplankton biomass in the upper 200 m of the water colum n was significantly higher (19-42 mg DW m(-3)) than has previously been rep orted for the Arctic Ocean, and it reached a maximum at ca. 87 degrees N in the Amundsen Basin. The lowest values were recorded in the Chukchi Sea and Nansen Basin, where ice cover was lower (50-80%) than in the central Arcti c Ocean. In the deeper strata (200-500 m) of the Canadian and Eurasian Basi ns, the biomass was always much lower (4.35-16.44 mg DW m(-3)). The C/N (g/ g) ratio for the mesozooplankton population was high (6.5-8.5) but within t he documented range, These high values (when compared to 4.5 at lower latit udes) may be explained by the high lipid content. Mesozooplankton accounted for approximately 40% of the total particulate organic carbon in the upper 100 m of the water column, Mesozooplankton species composition was homogen eous along the transect, consisting mainly of copepods (70-90% of the total number). It was dominated by four large copepod species (Calanus hyperbore us, C. glacialis, C. finmarchicus and Metridia longa), which together accou nted for more than 80% of the total biomass, According to measurements of g ut pigment and gut turnover rates, the mesozooplankton on average ingested between 6 and 30% of their body carbon per day as phytoplankton, Microzoopl ankton may have provided an additional source of energy for the mesozooplan kton community. These data emphasize the importance of mesozooplankton in t he arctic food web and reinforce the idea that the Arctic Ocean should no l onger be considered to be a "biological desert". (C) 1999 Elsevier Science Ltd, All rights reserved.