Seasonal variability in the bacteriolytic capacity of the deposit feeder

Although deposit-feeding macrofauna consume and digest sedimentary bacteria, it is unclear whether feeding rates and digestion efficiencies are high enough to significantly impact the composition and abundance of bacteria in marine sediments. It is likely that both feeding rates and efficiency of digestion vary markedly through space and time. We used a turbidimetric assay to compare the rate of bacteriolysis by digestive fluids collected seasonally from the deposit-feeding polychaete Arenjcola manna. Under standardized, experimental conditions, bacteriolytic rates represent concentrations of lytic agents. This concentration was found to vary significantly throughout the year [p = 0.001), showing greater than a 2 x range. Lytic agent concentration was positively correlated with bioavailable amino acid concentrations in the surface sediment [r = 0.85, p = 0.03) but showed no apparent relationship to other proxies for food resources (e.g. chl a), sediment temperature, or gut throughput time. In vitro, temperature has been shown to have a strong positive influence on bacteriolytic rate. Temperature has no influence, however, on the in situ concentration of lytic agent in gut fluids, thus it appears that compensation for this temperature dependence is unimportant. These findings, combined with previous kinetics studies with A. marina gut fluids, predict that the quantitative influence of deposit feeding on the microbial ecology of sediments will exhibit clear seasonal variation.