Spatial, seasonal and secular patterns in the cover of green algae on Heron Reef flat, Great Barrier Reef, Australia

The cover of green algae on the reef flat south of Heron Island was measured on 17 occasions between December 1990 and December 1995. Fleshy green algae cover increased seaward across the flat to about the middle, then decreased sharply. Seasonal variations in cover were also apparent: Chlorodesmis fastigiata was regularly more abundant in December and June than in March or September. Other species tended to show a single peak of abundance: Caulerpa cupressoides in June, C. fastigiata in March and Halimeda tuna in September. Tropical cyclone Fran passed over Heron Reef in March 1992 causing substantial changes to the fleshy algal cover, but not significantly reducing the total cover of fleshy green algae. However, Caulerpa racemosa and Chlorodesmis fastigiata showed an increase in cover following the cyclone with subsequent decline whereas Caulerpa cupressoides showed a compensating decrease in cover following the cyclone with a slow recovery over three years.