Will Ocean Acidification and Elevated Temperature Change the Swimming Behavior of Larval Stone Crabs?

The combined effects of coastal acidification and elevated seawater temperatures are changing the behavior, altering the physiology, and reducing the survival of larval crustaceans. One of the species that is being affected by these stressors is the stone crab, Menippe mercenaria, which is a $30 million dollar per year fishery in Florida. This study determined the impacts of reduced seawater pH and elevated seawater temperatures on the larval geotactic swimming response by monitoring larval stone crabs' swimming speed and directional orientation when exposed to both singular and simultaneous climate stressors. We used a fully-crossed experimental design with two treatments (pH and temperature) each with three levels (28℃, 30℃, 32℃; pH = 8.0, 7.8, and 7.6). Larvae were raised in each treatment and harvested at each larval stage (stages I–V) for geotaxis experiments. All geotaxis experiments were conducted in a light-tight room using individual larvae from multiple independent broods. We did not observe a difference in the upward swimming speeds, regardless of treatment.  The majority (> 65%) of stage 1 and 2 larvae swam upwards in all treatments; however, stage 3 larvae displayed a significant change in swimming direction when exposed to elevated temperature and reduced pH with only  28% swimming upwards. This change in swimming direction in the elevated temperature and reduced pH treatment suggests that stone crab populations may have difficulty migrating beyond their range with future changes in climate.