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Garrett, April Dawn

Biology

2021

M.S.

Given the unprecedented increases in atmospheric carbon dioxide and its projected negative impacts on organismal ecology and physiology, it is crucial to understand if and how organisms will withstand such environmental changes. Due to the oceans' service as a carbon sink, marine organisms face the added stressor of ocean acidification (OA), the process by which carbon dioxide mixes with water and decreases pH while simultaneously depleting the seawater of calcium carbonate. Marine organisms that rely on calcium carbonate for exoskeleton development are considered particularly vulnerable to OA, though previous results vary among species, leading to the question of who the real 'winners' and 'losers' will be in the face of increasing OA. Strongylocentrotus purpuratus, the purple sea urchin, is one such calcifying organism whose ability to respond to OA is relatively well studied in the past decade, but its future success still remains largely unclear. Within their natural habitat of the California Current Marine Ecosystem (CCME), there exists not only more extreme mean sea surface pH values as compared to the open ocean, but also high spatial and temporal variability due to a natural phenomenon known as upwelling. My thesis research aims to use theoretical and experimental tools from population genetics, experimental evolution, and ecological genomics to determine if developing purple sea urchins have the genetic capacity and physiological capability to respond to future OA in both static and variable extreme pH conditions. Low (pH 7.5) and extreme (pH 7.0) pH conditions led to decreased survival, with variability helping recover survival in those treatments. However, this recovery came with a trade-off: survivors in the extreme variable treatment were significantly smaller in body size compared to their static counterpart. Further, my work shows that purple urchins have the genomic capacity to respond uniquely to both extreme and variable pH conditions. While these results may be promising for the early life stages of the purple sea urchin, the carry-over effects of future low pH in the CCME on surviving larvae undergoing metamorphosis and developing into reproductive adulthood remain to be studied, as do the responses of marine species with lower levels of standing genetic variation in the face of increasing OA and pH variability in the CCME.