The role of oyster reefs in nutrient cycling and grazing within an estuarine ecosystem was observed by experimentally manipulating six tidal creeks. Reactive nutrient concentrations were significantly different in creeks with oysters when compared to creeks from which oysters had been removed. This evidence supports the hypothesis that oyster reefs function as nutrient retention mechanisms in these systems. There were no significant differences in Chlorophyll a concentrations among the creeks. This suggests that despite the increased grazing pressure exerted by these filter feeders plankton productivity may be enhanced in creeks with oysters.