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Article

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Published in: Proceedings of the 10th Symposium on the Geology of the Bahamas and Other Carbonate Regions, 2001.

Abstract

Coral cover and diversity are declining while macroalgal abundance is increasing in most Caribbean coral reef systems. Although a complex interaction of natural and anthropogenic disturbances is likely causal, the effects of a specific disturbance may vary dramatically for different reef systems. The coral reefs off the coasts of San Salvador Island, Bahamas and Belize, considered to be in relatively good condition, recently experienced near-direct hits by Hurricanes Floyd (1999) and Mitch (1998), respectively. In addition, NOAA scientists indicated that during 1998, tropical sea surface temperatures (SSTs) reached their highest levels above the normal annual maximum for this past century. With repeated monitoring of reefs off south­ central Belize and San Salvador Islan Bahamas, we have been able to document the severity of effects from these large-scale natural disturbances. Our patch reef and bank-barrier reef sites off San Salvador showed minimal damage from Hurricane Floyd, while our study sites on the forereef region off Belize were more heavily impacted by the passage of Hurricane Mitch. Although Agaricia spp. was the coral most strongly affected by the 1998 elevated SSTs on patch reefs around San Salvador Island (McGrath and Smith, 1999), we found scant evidence of bleaching of any coral colonies by January and June 2000. However, three-fold increases in partial colony mortality for this species are likely related to the bleaching stress. On the coral-reef ridges off south-central Belize, Agaricia tenuifo/ia experienced >90% mortality associated with the 1998 warming event. The mound and boulder corals were also strongly affected by elevated SSTs; > 50% of the colonies of Montastrea annularis complex and Diploria spp. were severely bleached. A major reef-builder, M annularis still showed widespread bleaching 9 months after the warming event, with -55% of the corals showing >50% partial colony mortality. Mean partial colony mortality was 2 to 5 times higher for reef sites monitored off south­ central Belize than San Salvador. For example, a major reef builder, Acropora palmata, showed a significant decline in partial colony mortality off San Salvador, while 75% of the colonies off Belize showed dramatic mortality. M annularis experienced similar, elevated trends of colony degradation on the Belize reef; the condition of the San Salvador population remained relatively stable over the two-year period. A combination of large-scale disturbances, including two coral bleaching events (1995 and 1998) and the effects of Hurricane Mitch have thus taken a dramatic toll on the Belize reef complex. The reefs off San Salvador Island showed notable resistance and resilience to these large-scale disturbances. We hypothesize that escalating anthropogenic impacts on the Belize barrier reef have exacerbated the effects of Hurricane Mitch and elevated SSTs; thus, full recovery from these back-to-back natural disturbances may be difficult and lengthy for this reef system.


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