Depth regulatory behavior of the first stage zoea larvae of the sand crab Emerita analoga Stimpson (Decapoda: Hippidae) |
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Authors: | Ronald S Burton |
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Institution: | Department of Biological Sciences, Stanford University, Stanford, CaliforniaU.S.A. |
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Abstract: | Laboratory studies of the behavior of first stage zoea larvae of the sand crab Emerita analoga Stimpson have shown that while newly-hatched larvae are strongly photopositive, this response lasts only about four hours, as the larvae rapidly become photonegative. After becoming photonegative, a large proportion of the larvae remain so throughout the first four days of life if they are fed Artemia nauplii; if starved, the larvae become significantly more photopositive than when fed. Both the photopositive response of newly-hatched larvae and the reversal to photopositive behavior in response to starvation are only apparent under horizontal test conditions. Increases in hydrostatic pressure stimulate swimming activity among the larvae; responsiveness to pressure being greatest at hatching and decreasing thereafter. The pressure response is strongly oriented to light; pressure-stimulated larvae will swim towards a light source regardless of whether this involves upward, downward, or horizontal motion. Experiments suggest that the pressure response provides the primary mechanism for depth regulation among young larvae; gravity and light may augment the pressure ‘sense’ by serving as primary orientational cues. The nutritional status of an individual larva may alter its depth-regulatory capabilities, but this effect is not yet clear. |
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