The nature and ecological significance of bacterial aggregation in a nearshore upwelling ecosystem

Abstract

Epifluorescent microscopic techniques were used to count free-living bacteria and to examine bacterial aggregations collected during a 24-day study of upwelling in a kelp bed on the west coast of South Africa. Free-living and aggregated bacterial numbers maintained constant proportions, 95% being free-living. The standing crop of bacteria fluctuated from 24 to 420 mg dry weight m −3 . Up to 34% of bacterial biomass was associated with aggregates, since attached bacteria were larger than free living forms. Six types of aggregate were recognized and hypotheses concerning their mode of formation are discussed in relation to environmental factors. It is suggested that aggregates and possibly free bacteria play a significant role in channelling energy flow from primary producers to the consumers, which were predominantly suspension feeders.