Zooplankton biomass distribution patterns along the western Antarctic Peninsula (December 2002)

Abstract

The phytoplankton [chlorophyll a (Chl a)], microzooplankton, mesozooplankton and macrozooplankton biomass and distribution were studied as part of a multidisciplinary project (Tempano) along the Antarctic Peninsula during December 2002. Even though the summer phytoplankton bloom was not yet developed in the area, autotrophs dominated the plankton biomass. Phytoplankton vertical distribution was, in general, homogeneous in the upper 40–50 m of the water column, further decreasing with depth. Protozoans showed low biomass; their contribution to the total plankton being one order of magnitude lower than that of autotrophs. The vertical distribution of protozoans was variable among stations with marked peaks at depths ranging from 30 to 80 m. Mesozooplankton-integrated biomass was generally low, although there was a notable increase southward near the ice marginal zone. Macrozooplankton distribution was more variable without any clear zonal distribution pattern. The vertical distribution of meso- and macrozooplankton (>4 mm) biomass showed clear peaks of abundance comprising different species depending on the geographical area. Our biomass distribution data suggest a food-web scenario in which macrozooplankton are preying on mesozooplankton populations only in the northerner stations, and mesozooplankton are, in their turn, shaping the abundance of the emerging populations of microzooplankton. Phytoplankton, on the other hand, seem to be hardly controlled by grazing activity.