The study examined the effects of Hurricane Hugo (1989) on the biota of Salt River Canyon, St. Croix. Although fish assemblages were not drastically altered, there were some changes in species composition after Hurricane Hugo. These differences related primarily to changes in sedimentary distribution during the storm. An order of magnitude decline in the abundance of echinoderms was also apparently related to sediment movement. Videotaped transects showed a decline in coral cover after the storm depths between 8 and 33 m. The greatest effect on a coral species population occurred at greater depths, where the fragile, Agaricia lamarcki experienced considerable damage from strong oscillatory flows during Hurricane Hugo. It appears that observed, hurricane-induced changes in fish, coral, and echinoderm assemblages can be directly related to physical processes.
Large-scale disturbances provide opportunities to observe community responses over a range of habitats at multiple sites. Despite their fortuitous nature and inherent statistical difficulties, the generalizations derived from 'natural experiments' can be more than conclusions based on smaller-scale field and laboratory experiments. Hurricanes have aroused interest among coral reef ecologists since Connell (1978) suggested their role in maintaing the diversity of sessile reef. That role, and the importance of other natural and anthropogenic perturhations, remain controversial (Jaclsson, 1991). How important hurricanes are to the balance between corals and benthic macroalgae, how hurricanes interact withmass mortalities of the urchin Diadima antillirum, and how these processes will affect community dynanics over the next several decades are pivotal in the ecology of Caribbean coral reefs Hughes, 1989; Knowlton, in press).
In 1980, Hurricane Allen devastated the reef at Discovery Bay, Jamaica (Woodley et al., 1981). Eight years later, Hurricane 'rt reset fore reef communities there to the conditions that prevailed immediately after Allen. long-term studies at Discovery ~ nearby sites (Knowlton et al., 1990; Hughes et al., 1987; Uddell and Ohlhorst, 1987; Precht, in press) have enhanced our ledge of hurricane effects. However, the pre-Allen ecology of these Jamaican reefs may have been atypical. Hurricanes pass to the north coast of Jamaica more ftequently than once per decade on average, but none had affected Jamaica for several Les preceding Hurricane Allen. Moreover, Discovery Bay is heavily fished, a condition that, along with 'i~ma dieoff, has contributed to post-hurricane alterations (Hughes et al. 1987). Studies elsewhere in the Caribbean have arnoderate to severe hurricane effects Rogers et al., 1991; Mah and Stearn, 1986; Edmunds and Witman, 1991; Fenner, 1991). Similar physical destruction was noted on some reefs in St. Croix, U.S. Virgin Islands following Hurricane Hugo, but, as with cane Allen, the severity of the impact varied from place to place (Woodley et al., 1981; Hubbard et al., 1991). The submarine canyon at Salt River, St. Croix) experienced currents up to 5 m/sec and wave heights of at least 3.5 m during Hurricane (Hubbard et al., 1991). Hard substrata were scoured by an enormous quantity of sediment that was transported down Salt River ~n and off the shelf. Yet post-storm visual aasessments suggested that fore reef damage at Salt River Canyon, as elsewhere along )north shore of the island, was less severe than at south-facing sites, which received greater wave energy (Hubbard et al., 1991). existence of pre-Hugo data on the composition of demersal fish, sessile benthic, and echinoderm assemblages provided opportunity to examine hurricane effects at a site where the biota initially appeared not to have been radically altered by the storm