Changes in a fringing reef complex over a thirty-year period: coral loss and lagoon infilling at Mary Creek, St. John, U.S. Virgin Islands

Recent decline in the diversity and percent cover of hard corals in reef environments worldwide has been extensively documented. To understand this decline, long-term records of reef environments are essential, but relatively few such records exist. The subject of this study is a fringing reef in the U.S. Virgin Islands, the Mary Creek reef complex (MCRC), located within the St. John National Park. Substantial changes have occurred in the MCRC over the last thirty years. in 1968, the reef crest zone was dominated by dense stands of A. palmata, and the reef was actively prograding; in 1986, few A. palmata colonies remained alive; and in 1998 only two living colonies, both small (about 30 cm high, with fronds less than 30 cm across), were recorded. During the same period the average water depth in the back-reef zone decreased, from about 1.5 m in 1968 to about 0.4 m in 1998, which corresponds to an average sediment aggradation rate of approximately 3.6 cm yr super(-1). The present situation in the MCRC may result from a combination of factors, and it is possible that the affected coral communities will reestablish in the future. The interplay of environmental stimuli and their effects on reef ecology, and in particular the role of time, are only beginning to be understood (Done, 1992). Therefore, the existing 30-yr record makes this site an excellent candidate for a long-term reef monitoring study.