STIMULATION OF MARINE FREE-LIVING AND EPIBIOTIC BACTERIAL-ACTIVITY BYCOPEPOD EXCRETIONS

The influence of marine copepod exudates (amino acids and NH4+) on act ivity by free-living bacteria, and the relative activity of epibiotic bacteria living on copepods were examined. Samples that contained cope pods (100 copepods l(-1)) were estimated to have leucine concentration s (K+S) that were higher by factor of 4.4, and leucine V-max's that we re higher by a factor of 1.8 relative to samples without copepods. NH4 + additions stimulated bacterial activity in samples that did not cont ain copepods, but had no effect in samples that contained copepods, su ggesting that free-living bacteria were N-limited. Epibiotic bacteria accounted for about 20% of total bacterial activity. These results sug gested that high-density copepod aggregations may liberate nutrients i n sufficient quantity to significantly stimulate bacterial activity, a nd that epibiotic bacteria may be optimally positioned to exploit thes e resources.