Consequences of global change for early life stages of the Olympia oyster

The nearshore marine environment is characterized by a multitude of natural and human-induced stressors. The interactive effects of stressors may complicate predicting ecological effects of global change on marine organisms. This dissertation focuses primarily on how altered seawater chemistry (ocean acidification), derived from increased atmospheric carbon dioxide, interacts with other environmental factors to influence the early life stages of Olympia oysters (Ostrea lurida). Initial laboratory experiments demonstrated that exposure of oyster larvae to high-CO2 caused lower growth rates and smaller size at settlement compared to individuals reared in ambient-CO2. Impacts were more pronounced a week after settlement, with juveniles exhibiting a larger decrease in shell growth rate compared to the negative effect on larval growth rate. The effects on juveniles arose regardless of the CO 2 level oysters experienced as juveniles, indicating a strong carry-over effect from the larval phase. A combined laboratory and field approach addressed the duration of carry-over effects and how effects might be moderated in the natural environment. Juvenile oysters reared in laboratory cultures under ambient and high-CO2 as larvae were outplanted to field sites at two intertidal shore levels that differed in emersion time and temperature regime. Larval exposure to high-CO2 led to reduced growth in juveniles. Juveniles outplanted to the more stressful shore level also exhibited reduced growth compared to individuals in more benign conditions. Effects persisted halfway to reproductive age, the duration of the study. To determine if the negative effects from ocean acidification would be exacerbated or ameliorated in a low or high food environment, respectively, oyster larvae were reared at two CO2 and three food levels. Larval growth was reduced in low food and in elevated-CO2 conditions, but these factors operated additively, indicating that the effects of high-CO2 on growth did not depend on the food regime. Settlement was lower in elevated-CO2 conditions compared to ambient, and this was especially true in low food conditions. High food levels did not completely eliminate negative effects of high-CO 2 on growth. A final experiment demonstrated that moderate temperature increases buffered larval and juvenile oysters from the damaging effects of high-CO2. Ocean acidification negatively impacts multiple early life history stages of Olympia oysters, and may contribute to substantial declines at the population scale. Responses are not uniform across the life cycle, and thus assessments of population responses to environmental perturbation must consider how effects propagate across life-history transitions.