TEMPORAL VARIATIONS IN THE DIET OF THE DAMSELFISH STEGASTES NIGRICANS(LACEPEDE) ON A REUNION FRINGING-REEF

The diet of the territorial damselfish Stegastes Nigricans (Pomacentri dae) was studied on a shallow coral reef flat of Reunion Island, S.W. Indian Ocean. Fishes were collected monthly from November 1989 to Augu st 1990 in order to examine their stomach and gut contents. The tempor al variability of the diet of S. nigricans was investigated on (1) a s easonal scale for the various size-classes and (2) a daily scale withi n two seasons. On average, algae accounted for 69.4% of the total weig ht of the stomach contents, all sizes combined. The total weight of al l prey, and both the weight and the percentage of algae in stomach con tents decreased in winter. This pattern was more pronounced for large (> 8 cm total length) and medium (4-8 cm) than for small individuals ( <4 cm). Small S. nigricans also fed on invertebrates such as polychaet es, ascidians and copepods, whereas medium and large individuals had a very low invertebrate consumption. Daily variations of diet were reco rded, with two maxima of food intake in summer: between 0600 and 0930 and between 1430 and 1900. In winter, only one peak of consumption was observed between 1200 and 1700. An estimate of food intake of 2488 g. m(-2).year(-1) (dry weight) for the S. nigricans population was determ ined from stomach and intestine contents. The seasonal variation in th e diet of S. nigricans may be related to several interacting factors, such as availability of food resources, high rate of consumption of fo od in summer for energy storage to offset the lean winter period, and high energetic needs for summer reproductive activities. The ontogenic shift in diet appeared to be a response of small individuals to both a transition phase between larval and benthic phases, and a need for p rotein-rich prey in order to promote their growth. The daily variation in the diet is probably due to diurnal variations in the nutritional value and/or palatability of algal food. (C) 1997 Elsevier Science B.V .