Diatom composition and biomass variability in nearshore waters of Maxwell Bay, Antarctica, during the 1992/1993 austral summer

 Diatom composition and biomass were investigated in the nearshore water (<30 m in depth) of Maxwell Bay, Antarctica during the 1992/1993 austral summer. Epiphytic or epilithic diatoms such as Fragilaria striatula, Achnanthes brevipes var. angustata and Licmophora spp. dominated the water column microalgal populations. Within the bay, diatom biomass in surface water was several times higher at the nearshore (2.4–14 μg C l^-1) than at the offshore stations (>100 m) (1.2–3.2 μg C l^-1) with a dramatic decrease towards the bay mouth. Benthic forms accounted for >90% of diatom carbon in all nearshore stations, while in the offshore stations planktonic forms such as Thalassiosira antarctica predominated (50–>90%). Microscopic examination revealed that many of these diatoms have become detached from a variety of macroalgae growing in the intertidal and shallow subtidal bottoms. Epiphytic diatoms persistently dominated during a 19-day period in the water column at a fixed nearshore station, and the biomass of these diatoms fluctuated from 0.86 to 53 μg C l^-1. A positive correlation between diatom biomass and wind speed strongly suggests that wind-driven resuspension of benthic forms is the major mechanism increasing diatom biomass in the water column. Received: 28 April 1995/Accepted: 1 April 1996     

Antarctic Phytoplankton Assemblages in the Marginal Ice Zone of the Northwestern Weddell Sea

The waters around the northern tip of the Antarctic Peninsulashow complex patterns of water circulation due to mixing ofdiverse water masses. Physicochemical properties of the differentwater types should affect the distribution, biomass and speciescomposition of the phytoplankton assemblages. We examined thesefeatures in the marginal ice zone (MIZ) of the northwesternWeddell Sea. Areas with the higher biomass were located in theWeddell Sea MIZ where the surface waters were relatively stabledue to the sea-ice melting. In these waters, the colonial stageof Phaeocystis antarctica and micro-sized chain-forming diatomsaccounted for 70% of the total phytoplankton carbon. Watersin the Bransfield Strait region, in contrast, were characterizedby a dominance of nanoflagellates, which accounted for 80% ofthe total phytoplankton carbon. Our observations support thehypothesis that the species composition of phytoplankton communitiesis a function of the different water mass, reflecting the physicalconditions of the upper water column, particularly its stability.