Abstract or Keywords
The combined effects of coastal acidification and warming seawater temperatures are changing species' behaviors, altering their physiology, and reducing their survival. One species that may be affected by these stressors is the Florida stone crab, Menippe mercenaria, which is a $30 million per year fishery. This study determined the impacts of reduced seawater pH and warmer seawater temperatures on the larval swimming response to gravity (geotaxis). We measured the swimming speed and direction of larval stone crabs when they were raised in treatment combinations of reduced seawater pH (pH = 8.0 and 7.6) and elevated temperature (28℃ and 32℃). Larvae were harvested at each larval stage (stages 1-5, n = 13 independent broods for stages 1-3; n= 6 for stage 4; n= 3 for stage 5) for geotaxis experiments, which were performed in a darkroom room. Our results show that there was no difference in larval upward swimming speeds. The majority (> 65%) of stage 1 and 2 larvae swam upwards in all treatments; however, there was a significant change in the swimming direction for stage 3 larvae in the combined temperature and pH treatment (only 28% swam upwards). Later-stage larvae also oriented downward. The change in swimming direction in the combined temperature and pH treatment (stage 3) suggests that stone crab populations may have difficulty migrating beyond their current range as coastal waters become more acidic and continue to warm.