Communities of Corals in Reef Ecosystems

Abstract

Most reef corals belong to the class Anthozoa. Only two of their families are related to another class of coelenterates-Hydrozoa: Milleporidae and Stylasteridae. The class of Anthozoa includes the two subclasses Hexacorallia (or Zoantharia) and Octocorallia, which are different in origin as well as in their morphology and physiology. The function of reef construction is mostly performed by the reef-building (or hermatypic) corals, which form massive calcareous (aragonite) skeletons. The group of hermatypic corals is represented mostly by the order Scleractinia (subclass of Hexacorallia). Two species in this group belong to the order of Octocorallia (Tubipora musica and Heliopora coeruled), and several species to the class Hydrozoa (hydrocorals Millepora sp. and Stylaster roseus) (see Fig. 7.1). The hermatypic corals harbor the algal symbionts zooxanthellae, which greatly accelerate the processes of calcification, thus enabling their host corals to construct massive colonies (cf. Sect. 1.2). The hexacorals from other orders of the subclass Hexacorallia: Corallimorpharia, Antipatharia, and Ceriantharia, including some species of the order Zoanthidea as well as most octocorals of the subclass Octocorallia, being colonizing animals, also produce hard skeletons or hard elements of their soft skeletons from the calcareous material, and thus participate in the production of crumb lime material.