Settlement and recruitment of a soft coral: why is Xenia macrospiculata a successful colonizer?

Rapid recruitment in the Red Sea soft coral, Xenia macrospiculata Gohar, 1940, depends largely on both its ability to migrate and its asexual reproduction. Colonization of artificial substrates and experimentally-denuded natural surfaces by this species takes place all year round. The migratory behavior of X. macrospiculata was detected as translocation of a wide size range of colonies from densely populated patches towards vacant neighboring spaces. The most intense colonization occurrs in the shallow reef (3–5 m), while in the deep zone (27–30 m) recruitment rate is lower. The migratory nature of X. macrospiculata enhances dispersion and enlarges the area of its aggregations. Furthermore, X. macrospiculata multiplies asexually by colony fission, facilitating dispersal and colonization capacity of this coral. Fission results in not only an increase of population density but also the regulation of colony size.

Colonization and space dominance exhibited by X. macrospiculata are largely due to vegetative processes. These features coupled with high fecundity, prolonged period of planulation and an early onset of reproduction, suggest that among Red Sea soft corals, X. macrospiculata, is situated on the "r" end point of an r–K continuum. Nevertheless, this species deviates from a "typical" r-strategist by displaying high competitive ability, which reinforces its success in maintaining high population density.