Seasonal and life-phase related differences in growth in Scarus ferrugineus on a southern Red Sea fringing reef.
Temporal trends in growth of the rusty parrotfish Scarus ferrugineus were studied on a southern Red Sea fringing reef that experiences seasonal changes in environmental conditions and benthic algal resources. Length increment data from tagging and recapture were compared among periods and sexes and modelled using GROTAG, a von Bertalanffy growth model. The growth pattern of S. ferrugineus was highly seasonal with a maximum occurring between April and June and a minimum between December and March. Body condition followed the seasonal variation in growth, increasing from April to June and decreasing from December to March. The season of maximum growth coincided with high irradiation, temperature increases and peak abundance of the primary food source, the epilithic algal community. There was a decline in growth rate during summer (July to October) associated with a combination of extreme temperatures and lowered food availability. There were strong sexual size dimorphism (SSD) and life-history traits. Terminal-phase (TP) males achieved larger asymptotic lengths than initial-phase individuals (IP) (L(∞) 34·55 v. 25·12 cm) with growth coefficients (K) of 0·26 and 0·38. The TPs were growing four times as fast as IPs of similar size. Three individuals changed from IP to TP while at liberty and grew eight times faster than IPs of similar size, suggesting that sex change in S. ferrugineus is accompanied by a surge in growth rate. The SSD in S. ferrugineus thus coincided with fast growth that started during sex change and continued into the TP. Faster growth during sex change suggests that the cost associated with sex change is limited.
Department of Ocean Ecosystems, University of Groningen, Nijenborgh 7, Groningen, 9747 AG, The Netherlands; Department of Applied Marine Science, College of Marine Science and Technology, P. O. Box 170, Massawa, Eritrea.
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Y
Afeworki
J J
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Videler
Y H
YH
Berhane
J H
JH
Bruggemann
D000818:Animals; D049628:Body Size; D004777:Environment; D005260:Female; D008297:Male; D008954:Models, Biological; D010473:Perciformes / Q000254:growth & development*; D012621:Seasons; D012727:Sex Characteristics
epilithic algae; growth spurt; monsoon; sex change; sexual size dimorphism; temperature