Meeting Abstract

P2.122  Friday, Jan. 4  Determinants of group size in the coral-associated fish, Dascyllus marginatus occurring in the Red Sea KOPLOVITZ, G*; KIFLAWI, M; University of Alabama at Birmingham; The Interuniversity Institute of Marine Sciences in Eilat, Israel and Ben Gurion University, Beer Sheva, Israel gilkop@uab.edu

Dascyllys marginatus is a planktivorous fish that exhibits a harem structure. Groups commonly inhabit colonies of branching corals with a preference for Stylophora pistillata. Group size is directly correlated with increasing sizes of coral colonies but this pattern displays considerable variation that may be accounted for by intraspecific competition for food, predation, or mating behaviors. Alternatively, group size could reflect random patterns established at the onset of juvenile recruitment. We measured whether group size in D. marginatus occupying different sized colonies of S. pistllata differed from that expected by chance or whether variation could be explained by seasonal changes in breeding status. In belt transect surveys conducted during the summer of 2005 (breeding season) and again in winter 2006, we measured the circumference of each S. pistillata encountered and counted numbers of associated D. marginatus. A computerized model was used to analyze whether fish group size varied randomly between corals. Quantile regression analysis indicated that there were significant differences between the observed distribution of fish group sizes and that predicted by a random distribution. On average, D. marginatus formed groups that were significantly larger than those predicted by a random recruitment model. Nonetheless, most individual coral colonies had fish groups that were well beneath carrying capacity as estimated indirectly by coral circumference. Fish group sizes tended to be greater during the summer breeding season suggesting that mating behaviors may be a contributing determinant of group size.