Corallum morphology and composition of crustacean cryptofauna of the hermatypic coralMadracis mirabilis

The motile crustacean cryptofauna of the hermatypic coralMadracis mirabilis (Duchassaing and Michelotti) was examined from three sites on reefs along the west coast of Barbados in 1985. In addition to site differences in degree of eutrophication, two distinct with-in-corallum habitats were recognized, based on differences in the growth form of the coral host. One form grows in isolated, hemispherical heads, with short, robust, widely separated branches covered by 50 to 80% live tissue. The second form occurs within large continuous beds of long, thin, tightly spaced branches tipped by 20 to 30% live tissue. Coral habitats consisting of small isolated heads support a crustacean fauna of high decapod and amphipod diversity, with numerous rare and site endemic species and an abundance of relatively large decapods and amphipods. The continuous beds favour a community of lower decapod and amphipod diversity, fewer rare and site endemic species and with an abundance of smaller sized isopods and copepods. It is suggested that spatial separation of branches and colonies as well as food availability associated with corallum morphology are factors influencing the variation in species abundance and faunal composition of the two habitats.