Neglected biodiversity and ecological functioning – fish community structure associated with Antipatharia (black corals) on shallow reef ecosystems

Erika Gress, Kevin Bairos-Novak, Tom Bridge, Gemma Galbraith

Addressing anthropogenic threats compromising the persistence of tropical marine ecosystems requires an understanding of the fundamental ecological functions these organisms fulfil. Habitat provision is a major function of corals in tropical marine ecosystems, although most research in this area has concentrated on scleractinians (hard corals). Here, we provide one of the first empirical studies of fish communities on shallow tropical reefs associated with another, lesser-known hexacoral group – the antipatharians (black corals). We quantify i) the abundance, and taxonomic and functional diversity of fish communities associated with antipatharians, and ii) the type of associations between the fish and the antipatharian colonies. Surveys were conducted on an artificial reef (SS Yongala shipwreck) and on a coral reef (Orpheus Island) in the central Great Barrier Reef, Australia. We documented 28 different species of fish within seven trophic groups and 23 functional entities associated with antipatharians, predominantly using the colonies as shelter. Antipatharians support both taxonomically distinct fish assemblages (>40% of species) and unique types of associations with the fishes. At the functional level, we observed large overlap in the fish community between antipatharians and scleractinians, reflecting their shared ecological roles, although antipatharians support significantly higher functional diversity. Given the similarity in functional composition of fish assemblages utilising both antipatharians and scleractinians, the presence of antipatharians may help buffer the effects of ongoing hard corals decline in tropical marine ecosystems. Overall, our study provides empirical evidence of the important role of antipatharians in supporting fish functional and taxonomic diversity on shallow tropical reefs.