Contributions to Zoology, 81 (4) – 2012Bert W. Hoeksema: Evolutionary trends in onshore-offshore distribution patterns of mushroom coral species (Scleractinia: Fungiidae)

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A phylogenetically based comparative analysis of onshore-offshore distribution patterns of mushroom coral species (Scleractinia: Fungiidae) was made to reconstruct an evolutionary scenario for differentiation in fungiid shelf habitats. This phylo-ecological study integrates data on fungiid distribution patterns along environmental gradients on the Spermonde Shelf, SW Sulawesi, with a recently published phylogeny reconstruction of the Fungiidae. A mushroom coral fauna of 34 species was used to compare their distributions by use of 50-m2 belt quadrats in transects (1) from the mainland to the shelf edge, (2) around reefs with regard to predominant wind directions, and (3) over bathymetrical reef zones. Species association ordinations were made for each of the four shelf zones using both abundance and incidence data to examine whether closely related species co-occurred. Some closely related species or even sister species appeared to show very similar distribution patterns and to co-exist in high abundances. These results indicate that there may not be community saturation and competitive exclusion among mushroom corals species, most of which are free-living. In reconstructions of fungiid habitat evolution, offshore reef slopes appear to be original (ancestral), whereas onshore habitats, shallow reef flats, and deep sandy reef bases seem to be derived. The latter is in contrast with an earlier hypothesis, in which deep sandy substrates were considered ancestral mushroom coral habitats.

Most studies on biotic changes of marine faunas along onshore-offshore gradients concern the evolution and extinction of taxa as represented in the fossil record. The general scenario is that marine faunas in the Phanerozoic originated in shallow coastal seas and expanded from there into deep offshore ecosystems, but also that some of the younger lineages may have originated in less stable nearshore environments (Jablonski and Valentine, 1981; Jablonski et al., 1983; Valentine and Jablonski, 1983; Jablonski and Bottjer, 1988, 1990; Sepkoski, 1991; Jacobs and Lindberg, 1998). With an increasing availability of phylogeny reconstructions based on molecular methods it is also possible to use recent taxa in studies on evolutionary trends in habitat preferences. Only few examples are known from the marine realm. For instance, Lindner et al. (2008) found that recent stylasterid corals (Hydrozoa: Stylasteridae), the second largest group of hard corals, evolved mainly in the deep sea, and invaded shallow waters from there.