Microbial aggregation and degradation of phytoplankton-derived detritus in seawater. II. Microbial metabolism

Detritus was generated from 3 different phytoplankton sources and kept in suspension in natural seawater. Rate and efficiency of mineralization to CO2 of both dissolved and particulate fractions and conversion to microbial biomass was estimated by the 'switching substrate' technique. There was a regular process of aggregation and disaggregahon of parhculate organlc matter associated with m~crobial utihzatlon of the detritus. Approximately half the carbon in both the dissolved and particulate fractions of the detritus was processed by the microbial community in about 2 wk at 26C. The natural microbial community appears to be capable of utilizing both the dissolved and parbculate organlc carbon in the detritus equally well, when available, enabhng the rapid circulat~on of nutnents and energy withn the mixed layer. While the relative importance of the dual role of the microbial loop as a carbon mineralizer or as a carbon incorporator may vary, the cumulative effect 1s probably always significant in terms of control over nutrient flow to the autotrophs or carbon flow to the heterotrophs.