Forms of the hydrozoan Millepora on a Recent coral reef

Publisher Website
Google Scholar
Abstract
Stearn, C. W. & Riding, R.: Forms of the hydrozoan Millepora on a Recent Cora reef. Distribution of the calcareous hydrozoan Millepora in the shallow water off the west coast of Barbados supports the view that morphologic variation in this genus is not primarily the response of a single species to environmental factors. Four forms are present on the fringing reef (1 to 6 m depth) and on an offshore ridge (11 to 17m depth). Branching, bladed, and boxwork forms co-exist at depths below 2 m and are thought to be genetically distinct (biospecies). They are equivalent to M. alcicornis, M. complanata, and M. squarrosa respectively. With decreasing depth they disappear in the order: branching, bladed, boxwork. This sequence reflects increasing colony strength and appears to be governed by increasing water agitation. The encrusting form is commonest in very shallow water, but also occurs in deeper water growing on gorgonians. It appears to be an environmental growth form of the other species.