Abstract
Microbiota colonizing silica grains of the same size and water pore space, but with a different microtopography, showed differences in biomass and community structure after 8 weeks of exposure to running seawater. The absence of surface cracks and crevices resulted in a marked diminution of the total microbial biomass measured as lipid phosphate and total extractable palmitic acid. With increasing smoothness of the sand grain surface, examination of the community structure showed a marked decrease in procaryotes and algal microeucaryotes, with a relative increase in microeucaryotic grazers. A comparison of the colonizing sediment incubated in running seawater or at 32 m on the sea floor with a sediment core showed a decreased bacterial biomass with a different community structure and a decreased total microeucaryotic population of both grazers and algae. The quantitative differences in microbial biomass and community structure between the microcosms and the actual benthic population in the core were determined.