Vertical swimming behavior in larvae of the Florida stone crab, Menippe mercenaria

Exogenous stimuli modify larval behaviors and mediate an individual's vertical position in the water column. Larvae (stages-1, -3 and -5) of the commercially important Florida stone crab, Menippe mercenaria, were used to determine if (i) individuals elicited a response to gravity (geotaxis), hydrostatic pressure and light, (ii) those responses underlie depth regulation and (iii) those responses change during larval development. All larval stages were negatively buoyant. Stages-1 and -3 larvae elicited a negative geotaxis that promoted upward swimming, while stage-5 larvae elicited behaviors that would position individuals at depth. During relative increases in pressure all larval stages tested swam up, while pressure decreases resulted in downward movement. Light intensities that mimicked an angular light distribution resulted in a negative phototaxis among all stages with stages-1 and -3 larvae being more sensitive than stage-5 larvae. These results indicate that the responses to exogenous stimuli in stone crab larvae function as a negative feedback mechanism for depth maintenance and change throughout ontogeny. The responses observed in stages-1 and -3 larvae suggest an overall shallower distribution while the shift in the sensitivity and orientation in stage-5 larvae likely positions individuals deeper in the water column, where sublittoral flow will facilitate transport toward settlement habitats.