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 (<30m 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 mu g Cl-1) than at the offshore stations (>100m) (1.2-3.2 mu g Cl-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 mu g Cl-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.