International audienceABSTRACT: On coral reefs, feeding by parrotfishes may prevent coral to macroalgal phase shifts by keeping algae in a cropped state. To predict the response of grazers to changing conditions, knowledge of the factors that affect feeding intensity is needed. Therefore, we studied food intake of the parrotfish Scarus ferrugineus on an inshore fringing reef in the southern Red Sea, Eritrea, where seasonality and extreme summer temperatures were expected to influence feeding rates. Bite rates (bites min-1), defecation rates (defecations min-1) and yield per bite (mass ingested bite-1) were estimated for 3 life-phase categories: 20 to 25 cm initial phase (IP), 30 to 35 cm terminal phase (TP) and 30 to 35 cm territorial terminal phase (TTP). The bite rates increased from low levels in the morning to peak values in the afternoon. IP bite rates increased linearly with seawater temperature. For TP, the temperature-bite rate relationship was quadratic, with maximum bite rates at ~32°C and lower rates at higher temperatures. Yield per bite in both IP and TP did not differ with time of year. Throughout the year, the total daily bites were highest in IP and lowest in TTP, resulting in ~23% lower daily intake in TTP compared to similar-sized TP males. Daily intake of ash-free dry mass of epilithic algal matrix (g AFDM d-1) was 7.5 to 9.6 for IP, 12.4 to 17.5 for TP and 8.7 to 13.2 for TTP. Intake and defecation rates and hence gut turnover rates peaked from April to July. The quadratic temperature response of TP suggests that large individuals may be close to their upper thermal limit, implying that temperature rises are likely to negatively affect grazing by large-bodied parrotfishes

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Feeding habits and territorial behaviour of four sympatric Red Sea butterflyfishes were investigated in Eritrean coastal waters. Individual bite rates and types of food consumed were recorded. Stomach contents of 125 specimens were analysed in the laboratory. The food items in the stomach were sorted and their volume estimated. The four species showed marked variation in their food preferences and feeding habits. The most abundant, Chaetodon larvatus, an obligate corallivore, forms monogamous pairs. Each pair defends a relatively small territory against conspecifics and C. semilarvatus. The latter species also feeds on scleractinian corals but is solitary or lives in small aggregations. The third species, Heniochus intermedius, feeds on non-coralline benthic invertebrates (mainly polychaetes); it usually lives in pairs or in aggregations of up to 24 individuals. Both C. semilarvatus and H. intermedius occupy undefended and overlapping home ranges. The least abundant species, C. mesoleucos, forms monogamous pairs, defends a territory and feeds mainly on non-coralline benthic invertebrates (mainly nematodes and polychaetes). The four species co-exist in the same habitat where they partition the food resources. Both C. larvatus and C. semilarvatus feed on scleractinian corals, but at different times; C. larvatus was observed to feed only during daytime, but C. semilarvatus feeds by day and night.