Effects of Hurricanes David and Frederic (1979) on Shallow Acropora Palmata Reef Communities: St. Croix, U.S. Virgin Islands

Hurricanes David and Frederic caused substantial damage to shallow Acropora palmata reefs off St. Croix, U.S.V.I., in the fall of 1979. We labeled 100 storm-damaged A. palmata branches, both attached and detached, in each of two forereef areas off the north shore (Buck Island forereef and Tague Bay forereef. Eleven months after the storms, 66% of these branches at Buck Island and 35% at Tague Bay were still alive. The rest were dead and covered with algae. Many of the surviving branches had healed completely and had initiated new offshoot branches. Healing rates ranged from 0.01–0.05 cm/day and the average size of branches which healed was significantly smaller than branches which died.

In south shore areas where pre-hurricane data existed, the structural complexity of A. palmata stands was reduced by nearly one half by the storms, and some areas were virtually flattened. At north shore study sites, the mean number of fractured branches per m² decreased significantly with depth.

Broken stumps on upright colonies and fragments which fell to the base of the reef were colonized by over 30 species of algae and 61 species of sessile invertebrates, including three species of scleractinian corals (Agaricia sp., Porites sp., and Favia sp.).

The influence of hurricanes on coral reef community diversity (both evenness and species richness) is complex. Evenness can remain the same or decrease through fragmentation of A. palmata colonies as many fragments survive and start new colonies. However, destruction of rapidly growing branching corals can increase diversity by providing more light for slower-growing massive corals and by providing new substrate for the colonization of algae and invertebrates.