A Regional Assessment of Dungeness Crab Vulnerability to Global Change: Insights from Model Projections

The Pacific Northwest coast of North America regularly experiences the effects of ocean acidification (OA) and hypoxia during the upwelling season. Conditions are projected to worsen in the future, posing risks for the economically and culturally important marine resources of the region, including Dungeness crab (Cancer magister). We diagnosed the vulnerability of multiple Dungeness crab life stages to present and projected future OA, hypoxia, and warming. Using a semi-quantitative framework, population level vulnerability was estimated from weighted life stage-specific exposure and consequence scores. Exposure scores were derived from the present and future (year 2100, RCP 8.5) conditions projected by a spatio-temporal regional ocean model. We calculated the percent exposure to low pH (<7.65), low oxygen (<2 mg/l), or high temperature (>15 °C) for the benthic and pelagic life stages using the bottom conditions and a physical larval transport model, respectively. Next, a literature review was used to score the relative consequence of each life stage’s exposure to the stressors. Exposure and consequence scores were multiplied to estimate stage-specific vulnerabilities. By combining stage-specific vulnerabilities with a population matrix model, we found that single-stressor impacts on the adult life stage contributed the most to population-level vulnerability. Although multi-factorial experiments are necessary to identify how multiple stressors interact to shape the vulnerability of Dungeness crab populations to global change, our results indicate that the younger stages (eggs and larvae) will be most vulnerable to ocean acidification, while the older stages (juveniles and adults) will be most vulnerable to hypoxia.