Seasonal Inertia of Macrozooplankton Communities in the Lazarev Sea

B.P.V. Hunt¹, E.A. Pakhomov¹, V. Siegel², U. Bathmann³

¹Department of Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, B.C., Canada, V6T 1Z4

²Sea Fisheries Institute, Palmaille 9, 22767 Hamburg, Germany

³Alfred Wegener Institute of Polar and Marine Research, Am Handelshafen 12, 27515, Bremerhaven, Germany

bhunt@eos.ubc.ca

Lazarev Sea macrozooplankton communities were sampled by RMT8 in the upper 200m of the water column in summer (December- January), autumn (April-May) and winter (July-August) during the German SO-GLOBEC (2004-2007). Diphyes antarctica, chaetoganths and euphausiids were the major contributors to total densities, each averaging > 10 ind.1000m^-3 in all seasons. Community Bray-Curtis similarities were ~ 68% within seasons and only slightly less between seasons (~ 61%). The major contributors to seasonal dissimilarity were Thysanoessa macrura (14 ind.1000m^-3) and Limacina helicina (0.7 ind.1000m^-3) occurring predominantly in summer, Euphausia superba occurring predominantly in autumn and winter (> 15 ind.1000m^-3), Eukrohnia hamata decreasing from ~ 7 to 1 ind.1000m^-3 between summer and winter, and the winter peak of Ihlea racovitzai (2 ind.1000m^-3). Changes were primarily attributed to migration out of the epipelagic layer and seasonal population decline. Overall, however, the similarity between seasons was high and total densities did not differ significantly between seasons, averaging 52.47, 59.14 and 46.28 ind.1000m^-3 in summer, autumn and winter respectively. In view of low winter primary production, it is predicted that the epipelagic had changed from bottom-up controlled in summer to top-down controlled in winter.