BIOGEOGRAPHIC STUDY OF THE PLANKTONIC COMMUNITIES OF THE PRINCE-EDWARD-ISLANDS (SOUTHERN-OCEAN)

Microphytoplankton and zooplankton composition and distribution in the vicinity of the Prince Edward Islands and at the Sub-antarctic Front (SAF) were investigated in late austral summer (April/May) 1996. Sampl es were collected for analysis of chlorophyll a concentration (Chl a), microphytoplankton and zooplankton abundance. Generally, the highest Chl a concentrations (up to 2.0 mu g l(-1)) and zooplankton densities (up to 192 ind. m(-3)) were recorded at stations within the inter-isla nd area while the lowest values (<0.4 mu g l(-1)) were observed at sta tions upstream of the islands. High Chi a and zooplankton biomass valu es were also associated with the SAF. Microphytoplankton were dominate d by chain-forming species of the genera Chaetoceros (mainly C. neglec tus), Fragilariopsis spp. and the large diatom Dactyliosolen antarctic us. The zooplankton assemblages were always dominated by mesozooplankt on which at times contributed up to 98% of total zooplankton abundance and up to 95% of total biomass. Among mesozooplankton, copepods, main ly Clausocalanus brevipes and Metridia lucens numerically dominated. A mong the macrozooplankton euphausiids, mainly Euphausia vallentini, E. longirostis and Stylocheiron maximum,and chaetognaths (Sagitta gazella e) accounted for the bulk of abundance and biomass. Cluster and ordina tion analysis did not identify any distinct biogeographic regions amon g either the microphytoplankton or zooplankton.