Sea ice microbial communities. III. Seasonal abundance of microalgae and associated bacteria, Mcmurdo Sound,...

Numbers of bacteria in annual sea ice increased directly with numbers of algae during the 1981 spring ice diatom bloom in McMurdo Sound, Antarctica. Algae and bacteria in a control site grew at rates of 0.10 and 0.05 day(-1), respectively, whereas in an experimentally darkened area neither increased after six weeks. Epiphytic bacteria grew at a rate twice that of the nonattached bacteria and were significantly larger, contributing approximately 30% of the total bacterial biomass after October. The microalgal assemblage was dominated by two species of pennate diatoms, anAmphiprora sp. andNitzschia stellata. Greater than 65% of epiphytic bacteria were associated withAmphiprora sp. after October.N. stellata, however, remained largely uncolonized throughout the study. We hypothesize that microalgae stimulate bacterial growth in sea ice, possibly by providing the bacteria with organic substrates.