Proteolytic activity in coastal oceanic waters: depth distribution and relationship to bacterial populations

Abstract

Peak proteolytic activities in the upper 100 m of the water column were more than 10 times those of deeper waters, though the natural substrate concentrations in the Santa Monica Basin have previously been found to vary by only 3 to 4-fold. Sediment porewaters were assayed during one cruise and found to have 20 to 30 times more proteolytic activity than the peak water column samples from the same cruise. Most of the proteolytic activity in the water column was associated with particles the size of bacteria (0.2 to 0.8 mu m) and, overall, total proteolytic activity was highly correlated with all bacteria variables tested. These results suggest that proteolytic activity in the water column is primarily associated with bacteria and is likely to be controlled by a number of factors related to the bacterioplankton, including biomass and growth rates.