Reference: Biol. Bull., 158: 283-294. (June, 1980) THE EFFECTS OF STARVATION ON PHOTOTAXIS AND SWIMMING OF LARVAE OF THE CRAP, RHITHROPANOPEUS HARRISII THOMAS W. CRONIN ' AND RICHARD B. FORWARD JR. Duke University Marine Laboratory, Beaufort. North Carolina 28516; and Department of Zoology, Duke University, Durham, North Carolina 27706 The phototactic response pattern of the zoeal larval stages of crabs, which was described for Rhifhropanopeus harrisii by Forward and Costlow (1974) and for various other light-adapted crabs by Forward (1977), is known to be altered by changes in environmental factors. Shifts in phototactic response have been de-scribed for R. harrisii larvae under conditions of altered salinity (Latz and Forward, 1977) and temperature (Ott and Forward, 1976), and for other species of crab larvae in altered pressure (Rice, 1964). It is likely that conditions in the internal environment also can influence phototactic behavior. Among these internal modi-fiers could be the nutritional condition of the larvae. In other crustacean zooplankton, including larval forms, feeding or the pres-ence of food has been reported to affect photobehavior. In Daphnia magna, Clarke (1932) found that positive phototaxis was minimal in media containing an abundance of food, but this effect could have been produced by the external medium. Lucas (1936) showed that the copepod Eurytemora hirundoidcs and the mysid Neomysis swam down, away from an overhead light, when in concentrated phytoplankton suspensions. On the other hand, Bainbridge (1953) reported that Caianus finmarchicus swam upward in overhead illumination when in the presence of phytoplankton. In the work of both Lucas (1936) and Bainbridge (1953), dark controls were not performed, so it is possible that the observed changes in vertical movement were not caused by a change in phototaxis. The most convincing work has been done with crustacean larvae. Singarajah et al. (1967) showed that starved stage-II nauplii of the barnacles Eliminus modestus and Balanus balanoides have enhanced positive phototaxis and reduced negative phototaxis when compared to fed nauplii. The differences were most pronounced when the experiments were done in the filtered media of algal cultures. Zoea larvae of the anomuran crab Emerita analoga also are more positively phototactic and less negatively photo-tactic when starved (Burton, 1979). This paper describes experiments to determine the effects of feeding on photo-taxis and swimming of zoea larvae of the crab Rhithropanopeus harrisii (Gould). Starved early-stage larvae showed increased positive phototaxis and in some cases reduced negative phototaxis. The swimming speeds in all stages were generally lower in starved larvae. MATERIALS AND METHODS Larvae for all experiments were obtained from ovigerous specimens of Rhithro-panopeus harrisii (Gould) collected from the Neuse River in eastern North Carolina. Crabs were maintained in filtered sea water at 25 C and 2Q f / (C salinity 1 Present Address : Department of Biology, 260 Whitney Ave., P.O. Box 6666, Yale Uni-versity, New Haven, Connecticut 06520. 283
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