Response of a benthic microbial community to biotic disturbance

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Abstract
The role of disturbance in natural microbial systems was studied by examining sediments disturbed by feeding sting rays and enteropneust worms. Biochemical measures based on the chemical components of cells were used to follow changes in the microbial community. The responses of the microbial community to feeding by rays, a mechanical disturbance to the sediments, were time-dependent. Several hours after the disturbance microbial metabolic status was shifted toward synthesis of phospholipid. Microbial growth rates were greater in disturbed sediments than in ambient sediment while microbial biomass was significantly lower in the disturbed sediments. Later, microbial biomass, growth rates and metabolic status were similar in the ambient and disturbed sediments. Ingestion and subsequent defecation of sediment by enteropneust worms also profoundly affected the microbial community. The biomass and growth rates of the microbial community were significantly lower in the fresh fecal castings compared to ambient sediment while metabolic status was shifted toward phospholipid synthesis. Six hours later, microbial growth rates were greater in the fecal castings than in ambient sediments while biomass had yet to recover. Groups of ester-linked, phospholipid fatty acids, each associated with a functional group of microorganisms, varied in their response to disturbance, indicating components of the microbial community varied in their response to disturbance. An a posteriori comparison of the ambient sediments from the several study sites, each receiving differing amounts of wave and tidal action, showed that abiotic factors also influenced the microbial community structure and metabolic status. This study presents evidence that biotic and abiotic disturbances may be important factors controlling the structure of microbial communities in estuarine sediments.