Turks and Caicos Islands 2006 coral reef assessment: Large-scale environmental and ecological interactions and their management implications

The Turks and Caicos Islands (TCI) has some of the best remaining reef in the Caribbean, but corals are declining as elsewhere in the region. Traditional reef assessment methods cover too little area to accurately characterize complex reef ecosystems, miss large-scale patterns, and high intrinsic spatial variability of reefs inhibits the ability to identify changes or causes. Spatially extensive surveys provide more information, over larger areas, in less time, than intensive ones, revealing large-scale gradients that intensive methods are inher - ently unable to identify. Extensive surveys were carried out in Providenciales, South Caicos, East Caicos, and Grand Turk. Live coral cover averaged 10-20%, maximum around 40%. Dead coral exceeded live coral at all sites. Several past mortality events from disease and high temperature were identified. Dead offshore elkhorn reefs, which protect the shoreline from erosion, are slowly crumbling from boring organisms. Stress from sedi- mentation was seen down-current from the Cruise Ship Port dredging site. Unexpectedly frequent and severe, but localized, coral disease was seen at many locations, often appearing in intense patches. A special focus of the survey was identifying algae distribution across environmental gradients. 26 ecological and environmental parameters were assessed at 47 coral reef sites across TCI. Transects were parallel and perpendicular to major environmental gradients and spanned their ranges. Correlations between all pairs of ecological and environmen - tal variables were assessed by non-parametric statistics. The matrix of all correlations and significance provided improved insight into interactions between species and their relations to environmental gradients, revealing that many diseases correlate with certain species of algae, which might be reservoirs for pathogens. High algae abun- dance was seen at almost all sites, with zoned gradients pointing towards nutrient sources. Most dive sites had little algae in shallows, but algae increased dramatically at the drop off edge into deeper water to the thermocline. In many shallow reefs algae zonation indicated land-based nutrient sources from outflow of creeks, marinas, salinas, fish processing plants, hatcheries, or groundwater seepage. Surprisingly high levels of algae were also seen at many remote sites with no land-based nutrient sources. Spatial zonation of algae suggest nutrient inputs from persistent localized upwelling of cold, deep, nutrient-rich water offshore. Green chlorophyll-rich surface water was noted at all sites affected by land-based sources or by offshore upwelling, suggesting widespread high natural nutrient backgrounds. Extensive methods are more cost effective than intensive ones and could be much more widely used for management purposes. The TCI data are being used to develop national water quality management and restoration strategies. Rev. Biol. Trop. 56 (Suppl. 1): 25-49. Epub 2008 May 30.