ENVIRONMENTAL-CONTROL OF MICROBIAL BIOMASS IN THE PONDS OF THE MCMURDO ICE SHELF, ANTARCTICA

Benthic cyanobacterial mats were the predominant form of vegetation in the many ponds on the McMurdo Ice Shelf. They attained a biomass of u p to 350 mg chlorophyll-a/m2. In contrast phytoplankton was always spa rse, rarely exceeding 5 mg/m2. We have examined a range of data from t hese ponds and hypothesise that low phytoplankton biomass was related to low inorganic nitrogen concentration in and loading to the ponds. B enthic biomass has accumulated over many years, in the absence of loss es to sloughing or grazing, and acts as a nutrient sink. Recycling of nutrients within the benthic mats appears to have prevented return of nitrogen to the water column. The only limit to biomass of the perenni al phytobenthos may have been self shading and the age of ponds.