The Effects of Ocean Acidification and Elevated Temperature on the Vertical Swimming Behavior Response to Light Cues in the Florida Stone Crab 

Light acts as a key cue for the vertical migration of larval stone crabs (Menippe mercenaria), by serving as a directional stimulus allowing individuals to change their position in the water column, and thus facilitates transport and dispersal. With the escalating challenges of coastal acidification and rising temperatures, stone crab physiology and behavior undergo compensation and can influence their phototaxic response to light. Such changes may potentially diminish larval survival and growth, change their relative depth distribution, and possibly alter dispersal. Such changes can consequently impact the $30 million per year fishery that relies on them. This study determined the impact of reduced seawater pH and elevated seawater temperature on the stone crab’s larval phototaxis response. The experimental design was fully crossed, encompassing two treatments (pH and temperature) at two levels each (28℃ and 32℃; pH = 8.0 and 7.6). Larvae from 12 broods were raised under each treatment condition, and phototaxis experiments were conducted at the first larval stage in a light-tight room using a set-up that mimicked the underwater angular light distribution. Our results indicate a shift from positive phototaxis when raised at 8.2 pH and 28°C to neutral and negative with 30°C and 32°C respectively. We found a negative phototaxis response in all three 7.6 pH treatments, with increased magnitude of response correlating with temperatures. These changes in swimming orientation relative to light  pose a potential barrier to upward migration during the day, disrupting the variable current speeds that these larval stages typically experience which may have negative implications for the population's dispersal.

This work was in part supported by funding from the NSF (award number OCE-2049047)