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Ocean Acidification and Valve Gaping Behavior of Adult Eastern Oysters

Paper Reviewed
Clements, J.C., Comeau, L.A., Carver, C.E., Mayrand, E., Plante, S. and Mallet, A.L. 2018. 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. Journal of Experimental Marine Biology and Ecology 506: 9-17.

Over the past few years there have been many studies investigating the effects of elevated pCO2 (i.e., ocean acidification) on the behavior of marine animal life, most of which have focused on fish. Unfortunately, marine molluscs -- bivalves in particular -- have been understudied in this regard; and hoping to help fill this knowledge gap, Clements et al. (2018) recently examined the effects of ocean acidification on the valve gaping activity of adult eastern oysters (Crassostrea virginica) in conjunction with acute heat shock. This valve gaping behavior, according to the researchers, is influenced by key physiological processes, such as respiration, feeding and metabolic activity and is often indicative of stress and overall animal health. Consequently, they say it "may be used to detect bivalve sensitivity to stressors such as elevated pCO2 and/or seawater temperature."

The experiment was conducted in a laboratory under controlled conditions, where adult oysters were placed in one of five different pCO2 treatments (1000, 1500, 2500, 5500 and 8000 µatm, corresponding to approximate seawater pH values of 7.7, 7.4, 7.3, 7.0 and 6.8, respectively). Following a ten-day acclimation period under such pCO2 conditions, the oysters were subjected to three-hour heat shock assays where Clements et al. acutely raised the water temperature approximately 18°C within a 30 minute period to simulate "an extreme future heat wave during low tide exposure in a shallow subtidal system." After the three-hour heat shock, the temperatures were immediately returned to original acclimation temperatures of ~11-12°C. Valve gaping behavior, therefore, was measured continuously three hours before, during and after the heat shock treatment.

So what did those measurements reveal?

As described by the authors, "regardless of pCO2 treatment, valve gaping activity increased slightly as temperature increased during the heat shock assay, peaked as temperature peaked, and plummeted once the temperature was lowered again." Consequently, Clements et al. report that 10-day exposure to ocean acidification conditions "had little effect on the response of oyster valve gaping activity to acute heat shock." And thus the six researchers conclude that "adult eastern oyster valve gaping activity is unaffected by variable conditions under near-future ocean acidification and warming," which lack of impact, as they note, has also been reported under comparable conditions for the valve gaping activity of Arctica islandica (Bamber and Westerlund, 2016) and Macoma balthica (Jakubowska and Normant-Saremba, 2015).

References
Bamber, S.D. and Westerlund, S. 2016. Behavioral responses of Arctica islandica (Bivalvia: Arcticidae) to simulated leakages of carbon dioxide from sub-sea geological storage. Aquatic Toxicology 180: 295-305.

Jakubowska, M. and Normant-Saremba, M. 2015. The effect of CO2-induced seawater acidification in the behaviour and metabolic rate of the Baltic clam Macoma balthica. Annales of Zoologici Fennici 52: 353-367.

Posted 27 December 2018