Detrital protein contributes to oyster nutrition and growth in the Damariscotta estuary, Maine, USA

The expansion of oyster aquaculture relies on identifying and utilizing estuarine conditions that enable the economical production of a filter-feeding species. Detrital complexes may provide nutrition to oysters between beneficial phytoplankton blooms. The upper Damariscotta estuary is the most successful aquaculture site in Maine for eastern oysters Crassostrea virginica. To examine the impact of labile detrital protein detected in this estuary on oyster growth, we monitored enzymatically hydrolysable amino acids (EHAA, labile protein), chlorophyll a (chl a) and particulate organic matter (POM) biweekly, along with continuous monitoring of temperature, turbidity, and chl a by a Land/Ocean Biogeochemical Observatory (LOBO) buoy. Oyster feeding and growth were measured biweekly in the field and in a controlled laboratory experiment to assess responses to detrital proteins. Phytoplankton alone provided insufficient nutrition for field oysters based on measured POM absorption rate, suggesting a role for additional organics such as detritus in oyster nutrition. Oysters readily absorbed phytodetritus under laboratory conditions and cleared phytodetritus with high efficiency under field conditions. Bioavailable EHAA in the field was nearly completely absorbed by oysters, unlike POM, and seasonal EHAA concentrations correlate well with field growth rates. These indications of protein limitation on oyster growth are not explained by phytoplankton, which cannot account for all EHAA, and are consistent with seasonally abundant, labile detrital protein and observed phytodetritus. Detrital protein influence on this species implies that EHAA measurements can improve aquaculture site selection, help determine nutritional carrying capacity of estuaries, and help explain clarification of water columns by these filter feeders.