THE EFFECTS OF STARVATION ON PHOTOTAXIS AND SWIMMING OF LARVAE OF THE CRABRHITHROPANOPEUS HARRISII

Abstract

The effects of starvation on the phototactic responses and swimming speeds of the zoeal larval stages of the crab R. harrisii were studied with a closed circuit television system. Larvae were tested after varying periods of starvation and in media with and without exudates of the food species (nauplii of Artemia salina). There was no effect of medium on phototactic response. Stage I and II zoea larvae became more positively phototactic and stage I less negatively phototactic after starvation. Later stages did not have altered phototaxis during starvation. The swimming speeds of starved larvae were generally lower than those of fed larvae, but there was no further reduction in the swimming speed after the first day of starvation. When kept in a 12:12 light:dark cycle, larvae of all stages consumed more food during the day than at night, but feeding in the dark was still effective. There probably is little effect of nutritional condition on phototaxis over the course of a day. The altered phototaxis of starved larvae would move them higher in the water column, where food is presumably more abundant, and would increase their opportunity to be carried into new regions of an estuary where they might encounter food. The reduced negative phototaxis and lowered swimming speeds of starved larvae probably would place them in increased risk of both predation and export from estuarine waters.