No abstract

Feeding ecology of three life phases of the parrotfish Scarus ferrugineus was studied on a southern Red Sea fringing reef by comparing availability and consumption of benthic algae during the monsoon hot and cool seasons. Dominant biota covering dead carbonate substrates were in decreasing order of importance: turfs on endoliths, turfs on crustose corallines, and crustose corallines. On the reef crest and shallow fore reef, composition of the biota changed seasonally. Cover of turfs on endoliths and turfs on crustose corallines was higher during the hot season, while crustose corallines and macroalgae (only on reef crest) increased during the cool season. Biota in the deep fore reef did not show seasonal variation. All life phases used similar resources and showed selective feeding in all zones. Turfs on endoliths, followed by turfs on crustose corallines, was the primary feeding substrate. These two sources represented over 92% of bites during both seasons. Crustose corallines, macroalgae, and living corals were negligible components being strongly avoided at all zones and seasons. Resource use varied seasonally on the reef crest and shallow fore reef, while it remained unchanged on the deep fore reef. Turfs on endoliths were consistently preferred in both seasons but their contribution increased from 45% in the cool to 70% of bites in the hot season. Electivity for turfs on crustose corallines shifted from random feeding in the hot (27% of bites) to selection in the cool season (47% of bites). Feeding pattern changed diurnally with more bites taken from crustose corallines and turfs on crustose corallines during morning. During the rest of the day, bites from turfs on endoliths predominate. S. ferrugineus shows limited capacity to exploit seasonal increases in the biomass of foliose and canopy forming macroalgae, despite indications of energetic limitation during the cool season.

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