Responses of Dendronephthya australis to predation by Dermatobranchus sp. nudibranchs

Abstract

The soft coral Dendronephthya australis occurs only in large abundance within the tidal-dominated Port Stephens estuary in eastern Australia. In recent years, substantial declines in the spatial extent of D. australis within Port Stephens has led to calls for the species to be listed as ‘threatened’. The causes for these declines are likely to include a range of anthropogenic impacts, as well as natural effects such as predation by the nudibranch Dermatobranchus sp., which can be abundant in winter and spring. The responses of D. australis to the presence of Dermatobranchus sp. were studied at two sites in Port Stephens, using time-lapse and still photography combined with visual surveys. Dermatobranchus sp. was observed consuming D. australis polyps, and colony inflation and polyp expansion were both reduced when Dermatobranchus sp. was present. Although predation by Dermatobranchus sp. is a natural impact, our observations suggest that interactions with additional anthropogenic stressors may exacerbate its overall impact on the spatial extent and survival of the geographically restricted soft coral D. australis.