Constancy of bacterial abundance in surficial marine sediments

Abstract

Controls on bacterial abundance in marine sediments remain poorly understood despite the importance to biogeochemical processes, benthic ecology, and in situ bioremediation. We report an analysis of direct microscopic counts of widely distributed surficial marine sediments, using a new approach of scaling abundance to the fluid volume of pore water within the sediments (bacteria FV−1). The analysis identified a greater constancy in benthic bacterial abundance than has been appreciated previously. Whether tested as a combined dataset or separately according to geographic region, less variance was observed when abundance was scaled to fluid volume rather than the traditional dimension of dry sediment mass. The decrease in variance suggests that the primary controls on abundance, such as nutrient acquisition or predator encounter rate, may also scale with porewater fluid volume. With values centered around 109 bacteria ml−1 FV, regulation must differ fundamentally from the water column, where values average 105–106 bacteria ml−1 FV.