Spatial prediction of coral reef habitats and coral reef community components was approached on the basis of the 'predict first, classify later' paradigm. Individual community components (biotic and geomorphologic bottom features) were first predicted and then classified into composite habitats. This approach differs from widely applied methods of direct classification based on remote sensing only. In situ coral reef community-condition assessment was first used to measure a response variable (percentage cover of habitat). Reef bottom features (topographic complexity, sandsediment, rock-calcareous pavement and rubble) were then predicted using generalized additive models (GAMs) applied to continuous environmental maps, high-resolution Ikonos satellite images and a reef digital topographic model (DTM). Next, using GAMs on newly created bottom maps, models were fitted to predict coral community components (hard coral, sea-grass, algae, octocorals). At this stage, high-resolution maps of the geomorphologic and biotic components of the coral reef community at an experimental site (Akumal Reef in the Mexican Caribbean) were produced. Coral reef habitat maps were derived using GIS following a hierarchical classification procedure, and the resulting merged map depicting 8 habitats was compared against thematic maps created by traditional supervised classification. This general approach sets a baseline for future studies involving more complex spatial and ecological predictions on coral reefs.
The explanatory value of four hypotheses for geographic variation in total species richness and species richness was evaluated per family in coral and fish communities in the North Sector of the Mesoamerican Barrier Reef System (NS-MBRS). The four hypotheses emphasize different reefscape attributes that are important for coral and fish: reef area (RA), live coral cover (LCC), habitat complexity (HC), and coral richness itself and for fish. For both coral and fish communities, we estimated the total number of species and number of species per family on 11 coral reefs along a 400-km section of NS-MBRS. Hard coral cover and HC were quantified using line and chain transects, respectively, and RA was estimated using Landsat TM images and a geographic information system. We used multiple regression and canonical redundancy analysis to study the fish-environment and coral-environment relationships. The three reefscape features (RA, LCC, and HC) in combination were much stronger explanatory variables for the observed biogeographic patterns of fish and coral biodiversity than they were singly. Coral and fish species richness were strongly correlated. Indicators of functional diversity (fish trophic groups and coral morphofunctional groups) followed the same biogeographic patterns as species richness. Reefscape attributes (RA, LCC, and HC) were shown to be good proxies for critical coral reef biodiversity values. This means that simple reefscape attributes can be used to predict more complex biodiversity values of different reef areas. Such predictions can provide an invaluable guide for regional biodiversity assessments, the extrapolation of these results to unsurveyed areas, and guidance for ecoregionalization within large reef tracts where data are sparse.
In 1999 Montastraea faveolata and M. annularis were the most numerous "large" (≥25 cm diameter) stony corals at ~10 m on fore reefs in the central and southern areas, respectively, of Quintana Roo, México. Reductions in live stony coral cover (from ~25% to ~12% in <10 years) and high recent partial-colony mortality (7-27.5%) are indications of declining reef conditions. Diseases in the five more northerly reefs, as well as tissue loss from the 1998 El Nino Southern Oscillation (ENSO) bleaching event and/or from on-going bleaching during June-July 1999 in the three southernmost reefs, appeared responsible for much of the recent mortality. Although turf algae predominated everywhere, macroalgae were relatively more abundant in the five more northerly reefs (four of which are in a reserve where herbivorous fishes currently are less numerous than further south). Additional perturbations associated with tourism development in the southern area could result in a loss of resilience of these coastal reefs.
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