Microbiology and Chemistry of Fecal Products of Pelagic Tunicates: Rates and Fates

Feces of pelagic tunicates contribute to benthic and pelagic detritus. Feces of freshly collected salps and doliolids, representing feeding done prior to capture, were collected. We examined the flux of phosphate, ammonium, and total primary amines between particles and water, the changes in numbers and kinds of microorganisms in the particles, the production of microbial biomass, and microbial respiratory rate. Bacterial populations which appear to originate in the feces develop rapidly during the first 24 h. During this time particles show a net uptake of phosphate, little change in ammonium, and a loss of total primary amines. Respiratory rate increases with the increase in bacteria. After 24 h protozoans invade the feces and rapidly consume most bacteria. Phosphate and ammonium are lost from the particles, and the respiratory rate drops sharply. By 50 h most of the microbial activity has terminated, and the particles begin to fragment further. Fecal particles are a potential food source for pelagic or benthic coprophages only for about 36 h on the average. If not ingested, they are rapidly utilized by their internal microbial community. The relative utilization by coprophages vs. microorganisms depends upon water depth and density of zooplankton. The efficiency of conversion of tunicate feces to microbial biomass appears to be 10–20%, which is comparable to other estimates of the efficiency of bacterial conversion of particulate matter.