SPATIAL PATTERNS OF GLUTAMATE AND THYMIDINE ASSIMILATION IN BRANSFIELD STRAIT, ANTARCTICA DURING AND FOLLOWING THE AUSTRAL SPRING BLOOM

Extensive temporal and spatial measurements of microheterotrophic metabolism obtained during the RACER (Research on Antarctic Coastal Ecosystem Rates) program were used to determine the importance of biological and physical characteristics of the water to microbial rates in situ. During the 4-month sampling period, the rate of [H-3]thymidine incorporation into macromolecules ranged two orders of magnitude over the RACER study area; [H-3]glutamate incorporation varied 170-fold. The highest mean values and greatest spatial variation in microheterotrophic activity occurred in January, during the decline of the seasonal phytoplankton bloom. Examination of relationships among hydrographic and biological variables was carried out through a study of spatial autocorrelation structure. Low-order positive, and high-order negative autocorrelations were associated with a gradient in biological activity from maxima in the northern Gerlache Strait to minima in Drake Passage. Primary factors correlated with microheterotrophic activity were total pigments (i.e. [Chl a + phaeopigment] concentration), total microbial biomass (i.e. ATP) and bacterial abundance. We also found evidence that the temperature history of a site had a stronger bearing on production than did contemporaneously measured temperature. The strength of interactions between microheterotrophs and other plankton components varied with time. The relationships that held during the phytoplankton bloom (December) were strengthened and modified during the period of most intensive microheterotroph activity (January), and then collapsed and were replaced by other relationships in late summer (March) when microheterotrophic activity was low throughout the study area.