CHLOROPHYLL-A CONTENT IN CELLS OF ANTARCTIC PHYTOPLANKTON

Material was collected from the Weddell Sea and the Bransfield Strait in January/April 1989. Data on size-taxonomic composition and biomass of phytoplankton communities and Chl concentration were obtained to es timate the chlorophyll ''a'' (Chl) cell content. Single cell fluoresce nce measured microscopically was used as a relative index of cellular Chl content of individual species. The relationship between the specie s composition of the algal communities and the ratio of phytoplankton carbon:Chl concentration (C:Chl) was found. Due to changes in species composition the average C:Chl ratio in March/April (56) was half that in January/February (115). The C:Chl ratio ranged from 24 to 215 (mean = 101) in the upper mixed layer and from 14 to 69 (mean = 37) in the pycnocline region. The distribution of cellular Chl within individual species showed lower heterogeneity in the mixed layer in comparison wi th that in the pycnocline and below. Below the mixed layer, population s consisted partly of dead cells with very low pigment content, while other cells had greatly increased cellular Chl. At several stations th is cellular Chl increase led to the formation of a deep Chl maximum.