Differential Coral Mortality

Observations of interspecific differences in coral mortality support the contention that mortality is a precondition for macroalgal dominance. Branching corals, including the two Acropora species, are particularly susceptible to hurricane damage. Both species were devastated in Discovery Bay by Hurricane Allen (Woodley et al. 1981).

Edmunds and Bruno (1996) compared the West Fore Reef at Discovery Bay to other reef sites along the north coast of Jamaica in 1995. Fishing pressure was historically heavy throughout the area studied, and Diadema had been absent for more than a decade. One comparison site was located at Dairy Bull, a few kilometers east of Discovery Bay. At the intermediate depth of 10 m, coral cover was considerably higher at Dairy Bull than at Discovery Bay (table 9.1), and macroalgal cover was lower (40% macroalgal cover at Dairy Bull versus 62% at Discovery Bay; Edmunds and Bruno 1996). A principal reason for the difference between sites was that the cover of M. annularis complex was much higher at Dairy Bull than at Discovery Bay. In fact, the cover of M. annularis was higher at Dairy Bull in 1995 than it was at Discovery Bay prior to Hurricane Allen (table 9.1).

The maximum skeletal growth rate measured for M. annularis is ~1.5 cm linear extension per year (Hudson 1981a,b). The average growth rate is lower: a 50 cm tall colony is approximately 50 yr old under good conditions (Dodge,

TABLE 9.1. Comparison of Coral Cover at 10 m Depth Between the West Fore Reef at Discovery Bay (WFR) and Dairy Bull, Jamaica."

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