Stimulation of marine free-living and epibiotic bacterial activity by copepod excretions

Abstract The influence of marine copepod exudates (amino acids and NH₄⁺) on activity by free-living bacteria, and the relative activity of epibiotic bacteria living on copepods were examined. Samples that contained copepods (100 copepods 1⁻¹) were estimated to have leucine concentrations (K+S) that were higher by factor of 4.4, and leucine V_max's that were higher by a factor of 1.8 relative to samples without copepods. NH₄⁺ additions stimulated bacterial activity in samples that did not contain copepods, but had no effect in samples that contained copepods, suggesting that free-living bacteria were N-limited. Epibiotic bacteria accounted for about 20% of total bacterial activity. These results suggested that high-density copepod aggregations may liberate nutrients in sufficient quantity to significantly stimulate bacterial activity, and that epibiotic bacteria may be optimally positioned to exploit these resources.