Significance of microheterotrophs in relation to the degradation process of subantarctic kelp beds (Macrocystis pyrifera)

Summary The abundances of the heterotrophic bacteria in relation to the degradation of the stranded kelp bed of Macrocystis pyrifera of the Morbihan Bay (Kerguelen Archipelago) were studied. During a one year period between the austral autumns 1982 and 1983 systematic observations of viable and direct counts of bacteria were recorded for three stations along a transect including kelp bed, intertidal and offshore waters. Quantitatively the microflora was very similar to that found in more temperate regions. Seasonal fluctuations were correlated with successive periods of deposit and degradation of the stranded kelp debris. After each new deposit, a very fast growing phase of the microbial population were observed. Doubling time (approximately 1.5 days) and biovolumes of the total bacteria showed rapid increases (from 0.16 to 0.38 m³). At the same time the ratio direct counts/viable counts showed a significant decrease and reached values close to 1. Decreasing number of bacteria were observed along the transect studied but the impact of kelp deposits on bacterial growth reached also offshore waters.