Drought and Consumer Outbreaks on Florida Oyster Reefs
In the Matanzas River estuary near St. Augustine, FL, my graduate student Hanna Garland and I investigated the causes of recently reported oyster losses on intertidal reefs. We found that the oyster reefs became increasingly deteriorated from the northern to southern end of the estuary, and that this deterioration was positively correlated with the abundance of carnivorous conchs and water salinity. We conducted caging experiments across these gradients, and found that oysters survived regardless of salinity if conchs were excluded, suggesting that conchs were the proximal cause of oyster loss. We then tested whether elevated water salinity was linked to conch abundance. In field experiments across a salinity gradient, we did not find any relationship between salinity and predation on conchs or on conch growth and survivorship. In a laboratory experiment, however, we found that conch larvae failed to survive at low salinities. Because this estuary’s salinity increased in 2006 in response to reduced inputs of freshwater, we concluded this salinity increase, by enabling an outbreak of carivorous conchs, was the ultimate cause of the oyster decline. Oyster conservation in the Florida ecoregion, which is probably one of the few that still support viable oyster populations, may be undermined by increased abundances of carnivorous conchs caused by drought-induced increases in salinity.
Garland, H. G., D. L. Kimbro. 2015. Drought Increases Consumer Pressure on Oyster Reefs in Florida, USA. PLoS ONE 10(8): e0125095.