| dcterms.abstract | Historically, coastal regions have supported large populations of biologically and commercially important shellfish species. However, in recent decades, the sustainability of these populations has been threatened by climate change processes that are contributing toward rising temperatures, hypoxic conditions, and acidified waters. Additionally, coastal zones receive river water, groundwater, and other sources of nutrient loading that further promote hypoxia and acidification. While previous studies have examined the individual effects of thermal stress, acidification, and hypoxia on bivalves, the interactions of these climate change stressors on these shellfish are poorly understood. My thesis was designed to investigate the interactive effects of thermal stress, acidification, and hypoxia on the growth, survival, and respiration rates of commercially and ecologically important North Atlantic bivalves: bay scallops (Argopecten irradians), Eastern oysters (Crassostrea virginica), blue mussels (Mytilus edulis), and hard clams (Mercenaria mercenaria). Month-long experiments were performed on ~one-month old post-set juvenile bivalves using conditions commonly found in the summer months within eutrophied, shallow, temperate, coastal environments (24-31°C; 2 – 7 mg O2 L-1; pHT = 7.2 – 8.0). Low levels of dissolved oxygen (DO) or pH or elevated temperatures were shown to negatively impact the survival, shell growth, tissue weight, and/or respiration rates of each bivalve species with A. irradians being the most sensitive. Thermal stress most frequently altered the performance of the juvenile bivalves with both positive and negative physiological consequences. Hypoxia resulted in lower survival, shell growth, and biomass for A. irradians, C. virginica, and M. edulis. Low pH conditions were most detrimental to A. irradians and M. mercenaria negatively impacting their survival and shell growth, respectively. Low DO and low pH frequently interacted antagonistically to yield shell growth rates higher than would be expected from either individual stressor, an outcome suggesting that anaerobic metabolism functions optimally under hypercapnia. Elevated temperature and low pH interacted both antagonistically and synergistically, again producing outcomes that could not be predicted from the response of the bivalves to individual stressors. Overall, my thesis demonstrated the unique interactions of multiple stressors related to climate change and eutrophication and that the combined effects of these stressors can be non-additive and sometimes more intense than their individual effects. | |
