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Effects of food supply on northern bay scallops Argopecten irradians (L.) reared under two pCO2 conditions

Samuel J. Gurr, Katherine McFarland, Genevieve Bernatchez, Mark S. Dixon, Lisa Guy, Lisa M. Milke, Matthew E. Poach, Deborah Hart, Louis V. Plough, Dylan H. Redman, George Sennefelder, Sheila Stiles, Gary H. Wikfors, Dianna K. Padilla, Shannon L. Meseck*

*Corresponding author:

ABSTRACT: For calcifying organisms, such as bivalves, short-term exposure to increased ocean acidification (OA; elevated pCO2) may reduce growth rate, increase mortality, and disrupt shell formation. A growing body of research suggests that clearance rates and what particles bivalves select may change under high pCO2 exposure, however these experiments are acute ranging from days to weeks. The effects of food supply on bivalves under long-term OA exposure remains incompletely understood. In this study, juvenile northern bay scallops, Argopecten irradians, that had been reared since 4 hours post-fertilization under one of two OA conditions (~500-600 or ~750-850 µatm pCO2; ~1.37-1.5 or ~1.0-1.2 Ωaragonite), were subjected to two food levels for 42 days (low food = ~400 and high food = ~1,400 chlorophyll cells mL-1). Standard metabolic rate (SMR) and clearance rate (CR) were measured at day 0 and SMR, CR, growth, and survivorship were measured at 14 and 42 days of exposure to two food levels for each of the OA treatments. Juveniles under food scarcity had reduced survivorship and growth independent of OA treatment. We found no effect of OA treatment, nor an OA by food interaction for these metrics. There was only a food level effect for SMR and no OA treatment effect; however, there was an interaction between food and OA for CR. Under elevated pCO2 concentrations, scallops cleared Chaetoceros neogracile (Chaet-B) over Tetraselmis chui (PLY429) and natural seston. Altogether, these data suggest that tolerance to OA mediated by food may depend on food quality or other characteristics that influence particle selection under short-term experimental challenges.