SEASONAL VARIABILITY IN THE BACTERIOLYTIC CAPACITY OF THE DEPOSIT FEEDER ARENICOLA-MARINA - ENVIRONMENTAL CORRELATES

Although deposit-feeding macrofauna consume and digest sedimentary bac teria, 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 u sed a turbidimetric assay to compare the rate of bacteriolysis by dige stive fluids collected seasonally from the deposit-feeding polychaete Arenicola marina. Under standardized, experimental conditions, bacteri olytic rates represent concentrations of lytic agents. This concentrat ion was found to vary significantly throughout the year (p = 0.001), s howing greater than a 2x range. Lytic agent concentration was positive ly correlated with bioavailable amino acid concentrations in the surfa ce sediment (r = 0.85, p = 0.03) but showed no apparent relationship t o 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 depend ence is unimportant. These findings, combined with previous kinetics s tudies with A. marina gut fluids, predict that the quantitative influe nce of deposit feeding on the microbial ecology of sediments will exhi bit clear seasonal variation.