Role of Flood Disturbance in Natural Oyster (Crassostrea virginica) Population Maintenance in an Estuary in South Texas, USA

A 2-year period with flood versus drought conditions provided the opportunity to examine the effects of flood disturbance on subtidal eastern oyster Crassostrea virginica biology and population dynamics in a south Texas estuary. Oysters were sampled monthly in 2007 and 2008 to examine the impacts of changing environmental conditions on oyster populations. Oysters were also examined quarterly for the presence of Perkinsus marinus. Filtration rates were calculated as a function of oyster size, temperature, salinity, and total suspended solids. Flood events in 2007 caused temporary reductions in salinity and were associated with reductions in oyster abundance, spat settlement, disease levels (weighted prevalence and percent infection), and filtration rates. Oyster populations had generally recovered within 1 year’s time—the oysters were younger and smaller but were just as abundant as pre-flood levels. The rapid return of oysters to pre-flood abundance levels is attributed in part to the ability of oysters in Gulf coast estuaries to spawn multiple times in a single season and in part to their relatively high growth rates. Although flood disturbance may temporarily reduce or destroy oyster populations, the ability of the Mission–Aransas Estuary to retain freshwater pulses within the system and maintain low salinities that are unfavorable for predators and disease can facilitate oyster population recovery. Episodic flood events appear to play a critical role in promoting long-term oyster population maintenance in the Mission–Aransas Estuary. The response of oysters to changing environmental conditions over the short term provides some insights into the potential long-term effects of changing climate.