Food intake by the parrotfish Scarus ferrugineus varies seasonally and is determined by temperature, size and territoriality

Abstract

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

Alternative male mating tactics of the endemic Red Sea parrotfish Scarus ferrugineus

“…TP < 30 cm fork length make up c . 50% of the TPs and are here considered non‐territorial (Afeworki, ).…”

“…During each spawning period, which may last for 1–3 h (Afeworki, ), a TTP was observed to pair spawn with a minimum of 0 and a maximum of 16 IPs, with an average daily rate of 6 ( n = 79). At the end of the spawning period, TTPs abandoned their territories and moved to the shallow reef zones to forage with conspecifics.…”

“…Small non‐territorial TPs in the population studied were abundant and their size range overlapped with that of the IP (Afeworki, ). These STPs are essentially a third social category of males and behavioural observations indicated that they adopt the same alternative mating tactics of streaking and group‐spawning as IP males.…”

“…Field observations were conducted from August 2007 to June 2008. During the daily spawning period (Afeworki, ), two observers using scuba gear haphazardly selected two TTPs and recorded spawning behaviour. Observers estimated the size of the TTPs (for details see Afeworki et al ., ) and recorded the incidences of spawning and chasing.…”

“…Since TTPs were typically >30 cm in fork length ( L F ) (Afeworki, ), terminal‐phase non‐territorial males <30 cm in L F were considered as STPs. Each spawning event was described by the type of participants: pair spawning between a TTP and an IP female (TTP–IP); pair spawning between an IP male and an IP female (IP male–IP); pair spawning between a STP and an IP female (STP–IP); group spawning defined as those spawning events that involved at least one female and more than one male.…”