Seasonal Patterns of Planktonic Production in McMurdo Sound, Antarctica

Abstract

The prolonged periods of continuous darkness and light in polar regions have resulted in a unique seasonal partitioning of primary and heterotrophic production. In McMurdo Sound for example, the biomass, size distribution and production by phytoplankton and bacterioplankton undergo distinct seasonal cycles. The seasonal pattern of primary production appeared to be regulated by light whereas the three order of magnitude change in phytoplankton biomass during mid- to late December was largely controlled by the advection of planktonic algae from the Ross Sea into McMurdo Sound. The size distribution of phytoplankton was highly seasonal; nano- and picoplankton were dominant from August through November while netplankton were more abundant in December and January. Seasonal variations of bacterial biomass and production were smaller than those of phytoplankton. During the late austral winter and spring, bacterial biomass and production exceeded those of phytoplankton. This implies that during this period, organic material from allochthonous sources sustained bacterial growth. During the late spring and summer, however, the pattern was reversed and autochthonous primary production was sufficient to support concurrent bacterioplankton production. The apparent temporal disequilibrium in autochthonous bacterioplankton and phytoplankton production was maintained by the seasonal input of allochthonous organic material into McMurdo Sound. The facts that a) bacteria were both abundant and highly active, b) bacterivory was common among many of the endemic protozoa and some planktonic metazoa and c) these bacterivores consumed >95% of the bacterial production strongly suggest that bacteria are a crucial component in the transfer of energy and material to metazoans in polar regions.