**2. The case of coral reefs in the Mexican Caribbean**

storms and waves, recreational opportunities and aesthetic and cultural benefits (see [4]). It is estimated that more than 100 countries have coastlines with coral reefs, and tens of millions of people depend on them as part of their livelihood or as part of their intake of protein [5]. It is noteworthy that the quantity and quality of these services depends on

Unfortunately, many of these ecosystems are in serious state of degradation and it is considered that the health of coral reefs is in a worldwide crisis [6]. By 2008 it was esti‐ mated that coral reefs had effectively lost 19% of their original area, an additional 15% was seriously threatened and was considered to it will be lost within the next 10 to 20 years, while 20% are under threat with the possibility of being lost within 20 to 40 years. These estimates were made under a scenario of 'business as usual' and do not consider

Paleoecologic work suggests that this pattern of degradation in various areas of the Carib‐ bean is unprecedented within the past millennia. Also, there is no convincing evidence that global stressors (e.g. induced bleaching by temperature changes and reduced calcification rates via increasing levels of atmospheric CO2) are responsible for the overall pattern of re‐ cent coral degradation, making it more likely that local stressors are responsible for the re‐ cent degradation occurred in the Caribbean [1]. In this sense, it is particularly evident that degradation of coral reefs occurs near densely populated areas, hence indicating that anthro‐ pogenic factors work synergistically against the stability of these ecosystems. Among these factors, the increased levels of nutrients and the over-exploitation of reef organisms are the best studied and considered to be responsible for the larger part of the impacts [8-9]. How‐ ever, we cannot omit mentioning other impacts such as increased discharge of sediment and pollutants, uncontrolled tourism and introduction of new species (e.g., lionfish) and diseases [2,4, 10-11]. Added to all these factors is the threat of global climate change and the in‐ creased intensity of natural phenomena such as severe storms and hurricanes, and the de‐ velopment of the El Niño / La Niña - Southern Oscillation phenomenon --and their associated surface temperature change-- have contributed to the health degradation of coral

In many locations around the world the anthropogenic stress on coral reefs has exceeded the regenerative capacity of the ecosystems, causing dramatic changes in species composition and thus a severe economic loss [2]. This change in the structure and functioning of the eco‐ system is known as "phase-shift" or alternative stable state; the most cited example is the shift from an original coral-dominated reef to one dominated by macroalgae[13-14], al‐ though several other transitions have been documented [2]. This phase-shift is a conse‐ quence of the loss of resilience, defined as the ability of an ecosystem to absorb perturbations, its resistance to change and its capability to regenerate after a natural or an‐ thropogenic disturbance [15]. The degree to which the phase-shift --or alternative state-- is stable or reversible is poorly understood and represents one of the main challenges for re‐

Given the nature of the problem and the huge importance of coral reefs to mankind, it is rec‐ ognized that urgent action is needed to conserve and promote its sustainable use [7]. Thus, it

the health of coral reefs.

30 Environmental Change and Sustainability

reef ecosystems [12].

search and management of coral reefs.

the threats posed by global climate change [7].

The degradation of coral reefs in the Wider Caribbean is alarming. Population growth in the region has led to a combined effect of increased pollution and reduced herbivore popula‐ tions as a result of overfishing and/or diseases [1,17]. These reefs are continually cited as ex‐ amples of a phase-shift.

In the case of coral reefs in the Mexican Caribbean (from the Northern tip of the Yucatan peninsula to the southern international border with Belize) studies are scarce and the poor distribution of the information generated from implemented management programs limits our knowledge of these systems and the successes of the conservation programs. In this sense, the current status and health of the coral reefs of the Mexican Caribbean at the region‐ al scale are not well known, but at the local scale, clear signs of deterioration have been re‐ ported in some reefs despite being designated and managed as protected areas. To achieve conservation and sustainable use of coral reefs requires a better understanding of the dy‐ namics of these ecosystems and the processes that support or undermine resilience; we need reliable scientific information that can be used for management plans at local and regional levels. This study presents the ecological and hydrological characterization of thirteen coral reefs distributed within three National Parks in the Yucatan: Isla Mujeres-Cancun-Nizuc Na‐ tional Park (PNIMCN), the National Park of Puerto Morelos reefs (PNAPM) and Cozumel reefs National Park (PNAC) (Figure1) in order to present the current state of these reefs and identify possible causes of degradation, if present.

For the analysis of coral/benthic community structure we used the following benthic diversi‐ ty indices: Margalef's D' index that measures species richness independently of the sample size, based on the ratio of the numberof species (S) and the total numberof individuals ob‐ served (N). Simpson's index of dominance (λ) that measures the probability from a non-re‐ peated random draw of two organisms from a community, that they belong to the same species. The Shannon-Wiener's index of diversity (H') measures the degree of uncertainty in predicting to which species belongs an individual chosen at random from asample of Sspe‐ cies and Nindividuals. Pielou's index of evenness (J') which measures the proportion of the diversity observed in relation to the maximum expected diversity with values ranging from 0 to 1, where values close to1 means that all speciesare equally abundant [18]. We used mul‐ tivariate techniques in order to statistically support the comparisons between localities, both in the community structure of coral and fish. A similarity matrix was generated using the Bray-Curtis coefficient of similarity; this coefficient measures the similarity between two samples with values ranging from 0 to 1, where values close to 0 correspond to different samples and close to 1 correspond to equal samples. Using the similarity matrix we per‐ formed an Analysis of Similarity (ANOSIM) for assessing the differences in community structure between locations. In addition a cluster analysis classification was performed in or‐ der to detect if a group of samples have more similarity to others within a group [19]. In the case of nutrient concentrations we applied a variance analysis (ANOVA) to detect statistical‐ ly significant differences between the parks studied.

**Figure 1.** Sampling localities at the Marine National Parks of Isla Mujeres – Cancún – Nizuc (PNIMCN), Arrecifes de Puerto Morelos (PNAPM) and Arrecifes de Cozumel (PNAC) during 2006 - 2007.
