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. Samples 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-island area while the lowest values (<0.4 mu g l(-1)) were observed at stations upstream of the islands. High Chi a and zooplankton biomass values were also associated with the SAF. Microphytoplankton were dominated by chain-forming species of the genera Chaetoceros (mainly C. neglectus), Fragilariopsis spp. and the large diatom Dactyliosolen antarcticus. The zooplankton assemblages were always dominated by mesozooplankton which at times contributed up to 98% of total zooplankton abundance and up to 95% of total biomass. Among mesozooplankton, copepods, mainly Clausocalanus brevipes and Metridia lucens numerically dominated. Among the macrozooplankton euphausiids, mainly Euphausia vallentini, E.longirostis and Stylocheiron maximum,and chaetognaths (Sagitta gazellae) accounted for the bulk of abundance and biomass. Cluster and ordination analysis did not identify any distinct biogeographic regions among either the microphytoplankton or zooplankton.