| Summary: | Anthropogenic greenhouse gas emissions, including carbon dioxide, are causing an unprecedented rate of global warming. Carbon dioxide emissions are additionally causing ocean acidification; a process that decreases the pH and carbonate saturation state of seawater. Ocean acidification is particularly stressful for marine calcifiers; organisms that build calcium carbonate shells or skeletons. Marine bivalves build calcium carbonate shells that they use as a support for their growing tissues, and as protection from predation. Bivalves are osmoconformers, and have limited mobility, meaning that they are particularly susceptible to the impacts of thermal stress. Bivalve fisheries generate billions of dollars to the US economy in annual revenue, therefore understanding their response to these two global change stressors is crucial for helping the communities that rely on these fisheries plan for global change. The following studies explore the response of commercially important bivalve species to ocean acidification and warming. Chapter 2 describes an experiment in which the response of king scallops Pecten maximus to ocean acidification was measured under spring and summer temperature regimes. This chapter also introduces the role of calcification site chemistry in dictating the calcification response to ocean acidification. King scallops were exposed to three pCO2 and two temperature treatments for 74 days. Their calcification rates were measured over the experimental period, and the pH of their calcification site (the extrapallial fluid), and tissue condition index were measured at the end of the experiment. King scallop calcification and condition index were resilient to ocean acidification, but showed opposing trends under different seasonal temperatures, highlighting the energetic tradeoffs between these two biological processes, and the importance of temperature in influencing the timing of these processes. Calcification rate was correlated with extrapallial fluid pH, demonstrating the importance of the ...
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