Effects of Elevated CO2 and Decreased Dissolved Oxygen on Phototactic Behaviors of Juvenile Dungeness Crab (Cancer magister)

Anthropogenic CO₂ emissions are increasing the concentration of CO₂ in the oceans, and contributing to ocean acidification (OA), while increasing ocean temperatures and eutrophication are causing decreased levels of dissolved oxygen (DO). Due to coastal upwelling and limited water flow, the Puget Sound ecosystem is naturally high in CO₂ and seasonally low in DO, making it particularly susceptible to increased acidification and hypoxia. Dungeness crabs (Cancer magister) are both ecologically and economically important to the Puget Sound region. To investigate the threat of low pH and DO to C. magister behavior, megalopae and juveniles were exposed to current and predicted future levels of pH and DO. Juveniles were then placed in a dark container with a single bright light, and movement and phototaxis were studied during three-minute trials. We hypothesized that low pH and low DO conditions would alter phototactic behaviors of juvenile C. magister, through changes in neurotransmission and metabolism. C. magister reared in control (High pH-High DO) conditions spent a greater proportion of their time near the light, and were significantly more likely to touch the light during the three-minute trial, as compared to juveniles in the other treatment conditions. These results suggest that future predicted CO₂ and DO conditions in Puget Sound could disrupt the behavioral and cognitive abilities of juvenile crabs, leading to decreased survival and recruitment in the C. magister population. Given the importance of C. magister to the Puget Sound, these population changes could have significant ecological and economic implications for the region.