| Summary: | The oceans are changing, globally and locally. Two stressors already impacting marine life on both scales are changing carbonate chemistry, whether induced by the worldwide increases in atmospheric concentrations of carbon dioxide termed ocean acidification (OA) or by small-scale spatiotemporal fluctuations in coastal waters; and contamination, caused by the countless anthropogenically-produced chemicals that enter the marine environment each year. The potential for these two stressors to interact, causing novel toxicity outcomes for marine life, has only been acknowledged in recent years. In this thesis, I investigate interactions between carbonate chemistry alterations and contaminants to explore whether certain aspects of animal physiology and contaminant chemistry consistently determine outcomes for marine invertebrates. Through a review of the state of knowledge on the biological impacts of these interactions, I highlighted key knowledge gaps. Whilst established models exist for the effect of freshwater pH on the toxicity of contaminants, this has rarely been investigated in a marine context. This was particularly significant for ionisable organic contaminants: in general, acidic compounds increase in toxicity within the OA-relevant pH range, whilst basic compounds decrease in toxicity. Additionally, there was strong potential for the fluctuations in carbonate chemistry which naturally occur in coastal habitats to alter the toxicity of pH-sensitive marine contaminants. To address these knowledge gaps, I first exposed two marine invertebrates, the common mussel Mytilus edulis and the king ragworm Alitta virens, to the pH-sensitive contaminant copper under a fluctuating pCO2/pH regime representative of coastal conditions and which was expected to increase its toxicity. Fluctuating pCO2/pH induced an extracellular acidosis of 0.2 units for mussels, likely contributing to the twofold increases in oxidative stress and DNA damage induced by copper compared to in non-fluctuating conditions. For A. virens, its ...
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