Limited flexibility in resource use in a coral reef grazer foraging on seasonally changing algal communities

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.

Size-dependent prey selection in piscivorous pikeperch Sander lucioperca and Volga pikeperch Sander volgensis shaped by bimodal prey size distribution

“…In other cases, E = −1 values were considered to be valid (a similar consideration was followed by Nunn et al , 2007 for false +1 E values). Bootstrapping procedure (10 000 simulations) was conducted on prey data by keeping resource abundance constant (Afeworki et al , 2011) to estimate the 95% c.l . of electivity values.…”

The distribution of herbivorous fishes on the Great Barrier Reef

“…Increased Wshing pressure on coral reefs appears to have negative impacts on rates of bioerosion by parrotWshes whilst grazing and sediment removal are relatively unaVected . Additionally, the role of parrotWshes in phase shift prevention may be limited by a lack of dietary Xexibility; early life stages of macroalgae within the EAM are likely to be consumed incidentally by parrotWshes, but maturing macroalgae that arise from the EAM when grazing pressure is low may be avoided by parrotWshes (see Afeworki et al 2011), limiting their further role in halting phase shift trajectories. Although most parrotWsh species were widespread on the GBR, their relative abundances often diVered considerably across the shelf as shown by the transition in the dominant scrapers from S. rivulatus inshore to S. psittacus on outer reefs.…”

Seasonal and life‐phase related differences in growth in Scarus ferrugineus on a southern Red Sea fringing reef

“…The study was conducted on the gently sloping fringing reef of Sheik Said Island (15° 35′ N; 39° 29′ E), Massawa, Eritrea. Despite its inshore location and proximity to the city of Massawa, the reef has high (30–50%) coral cover (Zekeria & Videler, ; Afeworki et al , ) and supports a diverse and abundant grazer community (Afeworki et al , 2013 b ). There is a low‐intensity, canoe‐based fishery around Massawa, but parrotfishes or other reef grazers are not targeted (Tsehaye et al , ).…”

“…Extreme summer temperatures strongly affect coral reef algal communities in the southern Red Sea (Ateweberhan et al , ; Afeworki et al , ). Large biomasses of canopy‐forming and foliose macroalgae build up and crustose corallines prevail in the shallow reef zones during the cooler part of the year (Ateweberhan et al , 2005 a , b , 2006 b ).…”

“…These are often associated with significant changes in the community structure, abundance, nutritional quality and productivity of benthic algae (Carpenter, 1985;Klumpp & Mckinnon, 1989;Diaz-Pulido & Garzon-Ferreira, 2002;Ateweberhan et al, 2006a). The intake rates or food preferences of herbivores often show parallel changes (Letourneur et al, 1997;Ferreira et al, 1998;Afeworki et al, 2011;Lefevre & Bellwood, 2011). These are likely to alter energy budgets, resulting in growth and reproductive variations in reef-associated grazers.…”