Competition for Space among Coral-Reef Sessile Organisms at Eilat, Red Sea
Abstract:The major benthic organisms occupying space in the coral reefs of the northern Gulf of Eilat are stony corals, soft corals and algae. Living coverage of these three groups served as the criterion for determining their relative utilization of space, in nine reef localities. Stony corals and algae are the major space utilizers on the reef flats, while soft corals represent a minor group. It is suggested that on the reef flats, stony corals and algae are the major competitors for space. Stony corals constitute the major group occupying space in all upper fore-reef zones (1–4 m depth), whereas living coverage of soft corals and algae is lower.
Space partitioning among the three groups, measured in one locality, in a series of transects to a depth of 29 m, indicates that below the reef flat soft corals and stony corals are the major components occupying space (approximately 70% of the available substrate), while algal cover is negligible. Living coverage of stony corals consistently increases from 10% at a depth of 4 m to 70% at 29 m. The most abundant group of soft corals at a depth greater than 3 m is the Xeniidae. The xeniids exhibit a pattern of successive decrease of living cover with depth (from 50% at 4 m to 5% at 29 m).
The most abundant species among the xeniids of Eilat is Xenia macrospiculata. This species is the first among the soft corals to colonize artificial substrates and denuded areas. A unique mechanism of active movement is described for this species. It is suggested that such active movement enables the coral to regulate its population size, maximize substrate utilization and hence, successfully compete for space with other benthic organisms.
Document Type: Research Article
Publication date: July 1, 1981
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