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Keywords: Caribbean, eutrophication, LTER (long-term ecological research), coastal settings, human ... - page 8 / 14





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For example, Hurricane Andrew hit southern Florida in 1992, affecting extensive urban areas and mangrove wetlands (Smith et al. 1994). Hurricane Mitch, in 1998, was a category 5 storm when it hit coral reefs, mangrove forests, and urban centers in Honduras, Nicaragua, and Guatemala. Forecasting the condition of ecosystem functions, ecosystem services, and nat- ural resource capital in the Caribbean region requires knowl- edge of large disturbances such as El Niño–Southern Oscillation (ENSO) events and hurricanes. These forcing functions have spatially specific effects on coastal settings, in- creasing the diversity in ecosystem structure and function across the coastal seascape. Since the 1970s, ENSO events have occurred more frequently and persisted longer (Trenberth and Hoar 1997). Temporal patterns in precipitation are strongly modulated by episodic events such as hurricanes and ENSO. Because these global phenomena are controlled by climate change, the frequent occurrence of extreme climate events in the Caribbean could be more relevant than the fluctuations of the mean climate (Stenseth et al. 2002).

Impacts of sea-level rise on coastal settings are better as- sessed using regional values rather than global averages (Church 2001). Most intertidal wetlands in south Florida and the Caribbean can survive the present regional rates of sea-level rise, which range from 1.2 to 2.3 millimeters per year. The sustainability of these intertidal wetlands relies on migrat- ing inland to areas of decreasing tidal inundation along undeveloped shores. However, activities associated with urbanization, such as tourism, infrastructure, and agriculture, can remove supratidal regions, restricting the migration of in- tertidal wetlands in response to climate change. An increase in sea level alone would not be enough to“drown”coral reefs (Kleypas et al. 2001), but the combination of sea-level rise and decreased water quality (e.g., increase in nutrient enrich- ment and turbidity) would result in flooded coastlines that could affect many coral reefs and change reef distribution at local and regional scales. Thus, sea-level rise in combination with eutrophication and increasing sea surface temperatures has the potential to modify reef distribution not only in the Caribbean region but globally (Kleypas et al. 2001). Caribbean countries, like other small island and coastal areas, face dif- ficult decisions in confronting the adverse effects of global cli- mate change and associated sea-level rise. Consequently, the vulnerability of coastal resources and infrastructure to sea-level rise increases constantly, highlighting the urgent need for an integrated framework for coastal management (Twilley et al. 2001).

Ecological vulnerability across environmental signatures The 13 sites in this overview illustrate the ecological vulner- ability of the coral reef–sea-grass–wetland seascape across different environmental signatures in coastal settings. Areas with different levels of disturbance need to be included in ecosystem assessment to advance our understanding of the trajectories that ecosystems follow after major changes attributable to human effects, natural causes, and their

850 BioScience • September 2004 / Vol. 54 No. 9

interaction (Vitousek et al. 1997). Our selected sites across the wider Caribbean include different degrees of human impact on the structure and function of ecosystems in diverse envi- ronmental signatures. The management variable (table 2) refers to projects that have been implemented to rehabilitate and restore coastal ecosystems at the coastal seascape level.

Coral reefs are one of the most conspicuous coastal ecosys- tems in the Caribbean Sea, where the second longest barrier reef in the world and largest in the Northern Hemisphere is located off the coast of Belize (Hughes 1994). Recent evalu- ations of the global decline in reef area describe the western Atlantic Ocean and the Caribbean Sea as the regions where the most serious losses are occurring (Gardner et al. 2003). The reefs of the Caribbean and adjacent coastal waters con- stitute about 12% of the global total and are major indicators of the environmental stress in the region (Wilkinson 2000). Degradation and destruction of reefs are caused by sedi- mentation, destructive fishing, poorly regulated mining and construction, and anthropogenic nutrient inputs (Szmant 2002). Current estimates indicate that 29% of the Caribbean reef areas are considered at high risk because of increased runoff and sedimentation caused by deforestation, nutrient contributions from hotel and shipping wastes, coastal con- struction, and mining.

Studies in the selected sites and throughout the Caribbean region have focused on monitoring changes in reef extension, in species composition, and in the frequency of events such as bleaching, herbivory, and invasion by fleshy macroalgae (Aronson et al. 2002). The sites with large areas of coral reef cover are Everglades National Park,Florida; Morrocoy National Park (Parque Nacional Morrocoy) and Los Roques,Venezuela; Bocas del Toro, Panama; Twin Cays, Belize; Celestun Lagoon, Mexico; and Sian Ka’an, Mexico (table 2).

Considerable efforts in the wider Caribbean have been dedicated to evaluating the damage caused by coral diseases such as white band, and by coral bleaching due to an in- crease of 1˚C to 2˚C in sea surface temperatures above mean monthly summer values (Skirving and Guinott 2001).A cur- rent paradigm suggests that a fixed bleaching temperature threshold of 1˚C to 2˚C above the present average sea tem- perature needs to be reevaluated, since a broad spectrum of responses indicates that the temperature threshold changes over time as a result of acclimation and evolution (Hughes et al. 2003). Current reports suggest a massive regionwide de- cline of corals across the Caribbean basin, with the “average hard coral cover on reefs being reduced by 80%, from about 50% to 10% cover, in three decades”(Gardner et al. 2003).Yet it is still not clear what the relative roles of climatic and local human factors are, and how they interact in determining the long-term trajectories of reef decline (Buddemeier et al. 2003).

Recent studies on species turnover in the Belize Barrier Reef have shown a significant shift of coral reef species over hun- dreds of square kilometers in less than a decade (Aronson et al. 2002). These results confirm the short temporal scale on which human activities affect coral reef habitats. For

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