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 associating with antipatharians, predominantly using the colonies as shelter. At the functional group level, we found high similarity (~80%) in the fish community between the sites, and between antipatharians and scleractinians. However, antipatharians supported both taxonomically distinct fish assemblages (>40% of species) and unique types of associations with the fishes. Overall, our study provides empirical evidence of the important role of antipatharians in supporting fish functional and taxonomic diversity on shallow tropical reefs. Our results suggest that previously neglected hexacorals can play important ecological roles on shallow tropical reefs, where scleractinians are not the dominant coral taxa.