Extension of Dendronephthya australis soft corals in tidal current flows

Soft corals from the Dendronephthya genus (family Nephtheidae) can change size over short periods by pumping water into their internal hydroskeletons. However, the drivers behind these size changes are not well understood. In a tidal-dominated estuary in eastern Australia, it was hypothesised that short-term changes in the size of Dendronephthya australis colonies occur in response to changes in tidal currents. This was tested by monitoring colonies over a period of several days using time-lapse photography. Colony extensions of up to 360 % were observed, and size changes exhibited a repeated pattern, with two maxima and two minima occurring in each tidal cycle, matching patterns in semi-diurnal tidal flows. A significant positive correlation between colony size and current velocity was identified, with size changes lagging currents. The results of the study provide valuable new information on the behaviour of D. australis and improve understanding of the environmental requirements for this species.