Marine microbial ecology off East Antarctica (30 - 80°E): Rates of bacterial and phytoplankton growth and grazing by heterotrophic protists

Abstract

Abstract Marine microbes ( 100% d−1 at the western ice-edge sites. Rates of bacterivory ranged from 0.4 - 2.6 d−1 and were correlated with bacterial concentrations, bacterial growth rates and longitude. Rates were highest in the eastern-most part of the survey, which was sampled last, reflecting the transition along the successional continuum toward a respiration-based, senescent, microbial community. Rates of herbivory ranged from 0.3 to 2.4 d−1 and were correlated with concentrations of microzooplankton and HNF combined, rates of phytoplankton growth, and latitude. Rates were highest at southern ice edge sites where concentrations of prey (as represented by Chl a) and microzooplankton were also highest. Cluster analysis of the concentrations of marine microbes and their rates of growth and grazing mortality identified 5 groups of sample sites that conveniently summarised the variability in the composition and function of the microbial community. Cluster groups differentiated between low Chl a (∼0.3 μg l−1) open ocean Antarctic Circumpolar Current (ACC) communities; and high Chl a (∼2.4 μg l−1) ice-associated coastal blooms at various stages between bloom formation and senescence. This partitioning of cluster groups can be used to determine spatial and temporal patterns of carbon transfer by the microbial loop within the BROKE-West survey area.