Bacteria, Protozoa and Organic Matter Composition in the Sediments of Terra Nova Bay (Ross Sea)
Spatial distributions of bacterial and protozoan abundance and biomass were investigated in the sediments of Terra Nova Bay (Ross Sea) at depths ranging from 36 to 223m, during January-February 1994. Microbial parameters were compared to the distribution of several food indicators (such as phytopigments, lipids, proteins, total and soluble carbohydrates) in order to provide quantitative information about the different components of the benthic microbial loop and identify which factors are responsible for microbial distribution. As suggested by the high content of chloroplastic pigment equivalents (on average 29.0 µg g-1 dry wt), proteins (1.9 mg g-1 dry wt) and carbohydrates (5.3 mg g-1 dry wt), the sediments of Terra Nova Bay were characterized by large amounts of deposited primary organic material. These values are among the highest reported for coastal sediments. Sediment organic matter was mostly composed of labile compounds and 98% of the total carbohydrate content was composed of soluble carbohydrates. Benthic bacterial densities were 1 to 2 orders of magnitude lower than those previously reported in Antarctic sediments or at temperate latitudes (on average 1.7 × 107 cells g-1 dry wt). By contrast, microprotozoa showed high densities (on average 873 × 103 cells g-1) and accounted for 11% of the total microbial biomass. Such high protozoan densities are comparable to those reported for highly productive systems. Bacteria and protozoa were significantly correlated with phytopigment and protein concentrations indicating a response to the organic matter accumulation. Protozoan density was significantly correlated to bacterial number and biomass. Microbial communities in Terra Nova Bay sediments appeared to be mainly bottom-up controlled (i.e. dependent upon food source and substrate availability). However, the close relationship between protozoa and labile compounds and the high protozoan to bacterial biomass ratio stress the relevance of benthic protozoa that may represent, in coastal Antarctic sediments, the main vector for the direct transfer of detrital carbon and bacterial biomass to metazoan food web.
KeywordsSoluble Carbohydrate Organic Input Heterotrophic Flagellate Labile Compound Organic Matter Composition
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