Short-term exposure to elevated pCO2 does not affect the valve gaping response of adult eastern oysters, Crassostrea virginica, to acute heat shock under an ad libitum feeding regime

Abstract

While many studies document effects of elevated pCO2 on coastal organisms, the environmental variability characteristic of coastal regions is often not directly tested. We tested for effects of elevated pCO2 on the valve gaping activity of adult eastern oysters (Crassostrea virginica) in response to acute heat shock that can occur in nearshore shallow coastal waters. In two consecutive experimental trials, oysters (n = 4) wired with Hall Effect biosensors (that measured valve gaping at one-second intervals) were exposed for 10 days at six different pCO2 treatments spanning a range currently observed in nearshore coastal regions, and predicted under near-future ocean acidification. After the 10-day acclimation period, oysters from each pCO2 treatment were exposed to a 3-h heat shock assay (11-12 ➔ 30 °C) and valve gaping activity was monitored continuously. During the heat shock assays, valve gaping activity increased with increasing temperature and then ceased when temperature was reduced back to 11-12 °C; however, these valve gaping rate increases during heat shock were not characteristic of overly-stressed oysters. Exposure to elevated pCO2 had no effect on the valve gaping response of oysters to acute heat shock. Our results suggest that the valve gaping responses of adult eastern oysters to acute temperature increases are unaffected by short-term elevations in seawater pCO2. Future studies incorporating the roles of local adaptation, food availability, and direct functional consequences of valve gaping (e.g. physiological rates, predator avoidance, response to environmental toxins) are warranted.