| Summary: | Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Biological Oceanography at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2019. Ocean acidification (OA) and related stressors, like warming, are occurring rapidly in coastal systems. There is concern about the impacts these stressors may have on the early development of species that use the nearshore as nursery habitat. The inshore longfin squid, Doryteuthis pealeii, plays an important role in the northwest Atlantic food web, and annually lays its eggs in the nearshore benthos during summer. This thesis sought to characterize morphological, physiological, and behavioral responses of D. pealeii embryos and paralarvae to OA. Experiments began in 2013, where I exposed squid eggs to a range of acidification levels (400 - 2200 ppm CO2) to uncover when the dosage impacts first appear (around 1300 ppm). To do this, I developed multiple methods to better characterize the morphological changes and surface degradation of statoliths due to acidification. This initial work demonstrated small-scale variability in response intensity, across hatching days and the breeding season. I ran swimming behavior experiments with subsampled paralarvae from 2013 - 2015 and developed a novel 3D recording and analysis tracking system in the process. The 2D data from 2013 showed significant decreases in time spent near surface, while 3D data in subsequent years showed slight impacts to activity and swimming velocity with increasing acidification. Overall, I ran experiments from 2013-2016, and compiled and compared these data using response ratios. I show that seasonal temperatures impact the baseline state of the paralarvae through parental condition, while acidification sensitivity appears driven by parental year class. Finally, I examined the interaction of acidification stress with warming, demonstrating an antagonistic relationship between these stressors for this life stage of this squid. ...
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