Functional role of the soft coral Dendronephthya australis in the benthic food web of temperate estuaries

The soft coral Dendronephthya australis, with its limited distribution along the central New South Wales (NSW) coastline, forms a habitat within the benthic estuarine environment that supports commercially significant and protected marine species. However, the functional role of the soft coral within this system is unknown. Organisms from primary producers through to secondary consumers were sampled from soft coral and sponge habitats inside the Port Stephens estuary, NSW, Australia in 2014. A food web model of the benthic habitat, created using stable isotopes of carbon and nitrogen, was used to describe the functional role of the soft coral in comparison to sponges, another important habitat for commercially significant and protected marine species. Primary consumers accessed a range of benthic and pelagic energy sources; however, secondary consumers were almost entirely dependent on pelagic energy sources. Soft coral and sponges accessed different primary sources for their energy requirements. There was no evidence that D. australis was used as a direct food source by consumers other than nudibranchs. In contrast, sponges were trophically linked with secondary consumers and are likely to play a direct role in pelagic energy transfer. Amphipods collected from the branches of D. australis were identified as major prey components in the diet of protected syngnathids, suggesting that while the soft coral functions as critical habitat, it is indirectly linked to higher trophic levels.