| Summary: | Thesis (Ph.D.)--University of Washington, 2019 In this dissertation I combine laboratory experiments and field observations across natural oceanographic gradients to investigate how crustacean zooplankton will be affected by ocean acidification (OA) and other co-occurring ocean changes. Anthropogenic emissions are increasing carbon dioxide concentrations in the atmosphere and ocean, causing declining seawater pH, increasing ocean temperatures, and decreasing dissolved oxygen concentrations. These changes have the potential to influence the metabolism, growth, and survival of crustacean zooplankton, such as copepods and krill, that act as critical prey items for higher trophic levels. Puget Sound, WA is a large coastal estuary with a wide range of pH and oxygen levels present in different areas and seasons. By coupling laboratory methods and field observations, a wide range of drivers and mechanisms of ocean change can be considered, forming a powerful research approach. In Chapters 2 and 3, I characterized the pH exposure of the copepod Calanus pacificus and the krill Euphausia pacifica in Puget Sound and reared their eggs and larvae under a range of pH conditions in the laboratory. I found that krill larvae are sensitive to reduced seawater pH and may already be affected by pH conditions in some areas of Puget Sound. In Chapter 4, I investigated the effects of elevated CO2 on the phytoplankton-copepod trophic link at two different temperatures, using the marine cryptophyte Rhodomonas salina and the calanoid copepod Acartia hudsonica. I observed complex shifts in phytoplankton fatty acid content and evidence of direct effects of CO2 on copepods, as well as indirect effects mediated through changes in the phytoplankton. In Chapter 5, I used enzyme activities as physiological indicators of how adult E. pacifica are affected by pH and oxygen in controlled laboratory conditions and across natural oceanographic gradients in Puget Sound. To characterize the high inter-individual variability displayed by this ...
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