Contents lists available at ScienceDirect Journal of Experimental Marine Biology and Ecology journal homepage: www.elsevier.com/locate/jembe Short-term exposure to elevated pCO 2 does not affect the valve gaping response of adult eastern oysters, Crassostrea virginica, to acute heat shock under an ad libitum feeding regime Jeff C. Clements a, ⁎ , Luc A. Comeau a , Claire E. Carver b , Élise Mayrand c , Sébastien Plante c , Andre L. Mallet b a Fisheries and Oceans Canada, Gulf Fisheries Centre, 343 Université Avenue, Moncton, NB, Canada b L'Étang Ruisseau Bar Ltée., Chemin des Huîtres, Shippagan, NB, Canada c Université de Moncton Shippagan Campus, 218 Boulevard J.D. Gauthier, Shippagan, NB, Canada ARTICLE INFO Keywords: Bivalve behaviour Carbon dioxide Global change Heat wave Ocean acidification Valvometry ABSTRACT While many studies document effects of elevated pCO 2 on coastal organisms, the environmental variability characteristic of coastal regions is often not directly tested. We tested for effects of elevated pCO 2 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 pCO 2 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 pCO 2 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 pCO 2 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 tem- perature increases are unaffected by short-term elevations in seawater pCO 2 . 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. 1. Introduction The impacts of elevated pCO 2 on marine life have received much attention over the past decade, largely due to the expected effects of elevated CO 2 (and associated changes to the carbonate system) on calcifying marine organisms (Orr et al., 2005; Ries et al., 2009; Kroeker et al., 2010, 2013). It is becoming increasingly recognized, however, that elevated seawater pCO 2 can also affect the behaviour of marine organisms (Briffa et al., 2012; Leduc et al., 2013; Clements and Hunt, 2015). Given that behavioural alterations are often the initial pheno- typic response of marine animals to environmental stress, elevated pCO 2 has the potential to influence the ecological processes char- acterizing marine communities (Nagelkerken and Munday, 2016). While recent years have seen a dramatic increase in studies testing for effects of elevated pCO 2 on marine animal behaviour, much of the literature is occupied by studies involving fishes (Clements and Hunt, 2015). Consequently, the effects of elevated pCO 2 on the behaviour of marine molluscs – particularly bivalves – have been comparatively understudied. For example, in a review of CO 2 -behaviour studies leading up to 2015, Clements and Hunt (2015) found that while 46% of studies focused on teleost fishes, only 20% focused on molluscan be- haviour, with a mere 7% on bivalves. Although typically sedentary, a number of behaviours in marine bivalves are evident, including clumping (Côté and Jelnikar, 1999), shell activity and closure (Smee and Weissburg, 2006a, 2006b), swimming (Winter and Hamilton, 1985; Ansell et al., 1991; Wilkens, 2006) and burrowing (Zwarts and Wanink, 1993; Zaklan and Ydenberg, 1997). Indeed, a number of bivalve be- haviours, including burrowing, are reportedly impacted by elevated pCO 2 in both sediment porewater (Green et al., 2013; Clements and Hunt, 2014; Rodríguez-Romero et al., 2014; Clements et al., 2016; https://doi.org/10.1016/j.jembe.2018.05.005 Received 27 September 2017; Received in revised form 4 May 2018; Accepted 14 May 2018 ⁎ Corresponding author. E-mail addresses: jefferycclements@gmail.com, jeffery.clements@dfo-mpo.gc.ca (J.C. Clements), luc.comeau@dfo-mpo.gc.ca (L.A. Comeau), ccarver@bellaliant.com (C.E. Carver), elise.mayrand@umoncton.ca (É. Mayrand), sebastien.plante@umoncton.ca (S. Plante), amallet@bellaliant.com (A.L. Mallet). Journal of Experimental Marine Biology and Ecology 506 (2018) 9–17 0022-0981/ Crown Copyright © 2018 Published by Elsevier B.V. All rights reserved. T