Impacts of climate change and habitat on the health and recovery of Salish Sea shellfish

Abstract

Global climate change is causing ocean acidification (OA), warming, and decreased dissolved oxygen (DO) in coastal areas, which can cause physiological stress and compromise the health of marine organisms. In the Salish Sea, a region that already experiences naturally low pH and seasonal hypoxia and is surrounded by urbanized and industrialized areas, climate change will pose further threats to both economically and ecologically important shellfish species. The first part of this dissertation focuses on trace metal accumulation in mussels (Mytilus galloprovincialis), an important harvested species, and Olympia oysters (Ostrea lurida), Washington’s only native oyster species, and how oceanographic variables that will change with the climate may impact this metal accumulation. Our field study found differences between sites in both the mean metal concentrations and variability around the mean of those concentrations in bivalves. High metal concentrations in bivalves were not associated with high concentrations of metals in seawater. While we could not eliminate possible confounding factors, we also found higher metal concentrations in shellfish associated with lower pH, lower temperature, and lower dissolved oxygen. These findings increase our understanding of spatial differences in trace metal bioaccumulation in shellfish from the Salish Sea. The rest of this dissertation focused on another native Washington shellfish species, the endangered pinto abalone (Haliotis kamtschatkana), which declined by 97% in the state between 1992 to 2017. Their decline is a loss for indigenous tribes, recreational divers, and the health of subtidal rocky reefs and kelp beds. Starting in 2007, conservation aquaculture initiatives to restore pinto abalone have been underway to return the wild population to a self-sustaining level. However, the success of abalone depends not only on restoration efforts but also on the capacity of outplanted abalone to survive and reproduce as threats of ocean acidification and warming continue to increase. We conducted two hatchery-based experiments exposing abalone to different pH and temperature conditions (7.90-7.95 pH/14 °C (ambient), 7.90-7.95 pH/18 °C, 7.55-7.6 pH/14 °C; and 7.55-7.6 pH/18 °C), as well as testing the efficacy of coralline algae (CCA) as a settlement cue and substrate. In our first study, we found that abalone in the ambient treatment had the best survival, those in the 7.60pH/18°C treatment had the worst survival, and those in the two single-stressor treatments had survival in between. For surviving larvae, temperature appeared to have a minor effect on settlement; pH was the dominant stressor determining settlement success, with higher settlement rates for surviving larvae under ambient pH treatments at both temperatures. In our second study, juvenile survival was negatively impacted by low pH but positively impacted by CCA presence. Our results show the potential of CCA to increase pinto abalone juvenile survival and ameliorate the negative effects of low pH. We also conducted a field-based study comparing the survival of outplanted hatchery-reared abalone to oceanographic conditions at abalone restoration sites in Washington. We found clear differences in salinity and temperature variability between sites. Dissolved oxygen and pH both changed seasonally, and variability increased during spring and summer months with algal growth, but clear spatial patterns could not be determined. Current speeds also varied between sites, and currents seemed to be mostly tidally driven as opposed to having seasonal shifts. Overall, we could not determine clear correlations between any oceanographic variables and abalone survival, but our study provides important data on conditions abalone experience in the wild in Washington and will allow us to track how these conditions change over time.