Online

Ashlock, Lauren W.

Biology

2022

Ph. D.

Marine ecosystems provide essential habitat to ecologically and economically impactful species and provide humans with a wealth of ecosystem services. With climate change, marine ecosystems are increasing in mean temperature and temperature variability. Marine ectotherms are vulnerable to this change and are important sentinels of warming, as their internal physiology is dependent on the external thermal environment. Copepods are marine ectotherms that play a critical role in trophic transfer and nutrient cycling. Importantly, copepods are relatively short-lived, allowing them to track ocean change as it happens. Together, these qualities make copepods a reliable model for understanding the impacts of global change on marine ectotherms. In this dissertation, I assess the impact of climate change on copepods through three strategies, 1) Examining the vulnerability of the nutrient rich copepod Neocalanus plumchrus to ocean warming, 2) Investigating the roles of plasticity and adaptation in copepod response to climate change stressors, 3) Testing the importance of latitude and life history stage in determining copepod thermal tolerance. My results reveal the nutrient rich copepod Neocalanus plumchrus and the numerically dominant copepod Acartia tonsa are potentially vulnerable to continued warming. Integrating ten years of plankton survey data with satellite temperature data, I find that thermal thresholds vary by copepod species and that the most nutrient rich species, Neocalanus plumchrus, has a relatively low upper thermal threshold for occurrence of 11.5°C. Additionally, results demonstrate that N. plumchrus abundance was reduced during the 2014-2016 marine heatwave. With experimental methods, I demonstrate that Acartia tonsa thermal tolerance is reduced after rapid salinity shock, indicating its susceptibility to simultaneous salinity and temperature change. Together these results indicate that copepods are vulnerable to continued climate change. My research also elucidates important determinants of thermal tolerance in the copepod Acartia tonsa. Using experimental evolution, I find that development at ocean warming conditions imparts the same level of thermal tolerance as >50 generations of ocean warming. Additionally, through field collections and two generations of common garden conditions, I find that thermal tolerance varies with latitude, with copepods from Maine having lower thermal tolerances than copepods collected in New York and Florida. Importantly, we also find that juvenile A. tonsa are more thermally tolerant than larvae and adults. These results highlight the importance of plasticity in defining thermal tolerance, emphasizing the importance of the developmental environment for marine ectotherms. Additionally, results reveal that thermal tolerance is specific to life history stage and latitude of collection.