Species Concepts in Extant Scleractinian Corals: Considerations Based on Reproductive Biology and Genotypic Population Structures

Challenges to the biological species concept, arising primarily from studies of plants, continue to prompt discussion on the nature of species and on appropriate criteria for their definition. A review of techniques used to define species limits in scleractinian corals indicates that a phenetic species concept is generally adhered to, but that there is also a tacit acceptance of the biological species concept. The available information on asexual reproduction, breeding systems, and dispersal, relevant to discussions of interbreeding barriers and gene flow, is discussed to assess the applicability of the biological species concept for extant scleractinian corals. It is concluded from preliminary data that, although corals utilize many of the varied breeding strategies and modes of asexual reproduction described for plants, they differ in their lack of exclusively asexual species, their inability to hybridize successfully, and in the requirement of broadcast spawning corals for a minimum developmental period during the dispersive larval phase. At present, there is no evidence to discount gene flow as a cohesive force in maintaining scleractinian species nor to reject the biological species or recognition concepts as inappropriate for this group. However, presently described coral species are equally compatible with the evolutionary and phylogenetic species concepts. It will not be possible to resolve questions concerning the cohesive force(s) that bind species within the Scleractinia until further studies on the breeding systems, fertilization biology, hybridization, and genotypic population structures of extant corals, and on species persistence in the fossil record are undertaken.