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Interactions between multiple stressors (climate change, pollution, and overfishing) can erode ecological thresholds and trigger a phase shift from a coral-dominated reef state to less desired benthic states. Akumal Reef located in the North of the Mexican Caribbean is an important case study to quantify the ecological changes of coral reefs affected by multiple stressors. Here we used both field data (benthic cover, coral condition, fish biomass), together with satellite data of the main stressors (degree heating weeks, chlorophyll a, and urban area), to (i) reconstruct the timeline of stressors that have affected Akumal Reef from 1995 to 2019; (ii) describe the changes in coral reef components (benthic cover, bleaching, coral diseases, and fish biomass) in this period; and (iii) propose a model integrating coral benthic changes and the significant stressors influencing those changes through time while taking into account stressors interactions and partial effects. Our results show that between 1995 and 2019, hard coral cover suffered an average absolute loss of 84%. This loss contrasted with an average absolute gain in total algae cover of 74% and was negatively associated with an increase of 290% in the urban area. During the study period, there has been no signal of positive recovery in hard coral cover, and increasingly available space has been occupied alternatively by filamentous algae or macroalgae after acute stressor events, such as bleaching or disease, which are more frequent, and persistent in the last decade. Our integrative model highlights interactions between urban area, maximum degree heating weeks, and chlorophyll a as main drivers of hard coral decrease, as well as interactions between urban area and precipitation, related to total algae increase. Akumal Reef degradation trend must be rapidly addressed by implementing management tools integrated into a comprehensive coastal planning model, which must reduce pollution and overfishing, allowing the recovery of its structure and function, and providing persistence of ecosystem services in a context of global changes and ecological ‘surprises’.

Coral decline in the Caribbean is marked by the loss of habitat-forming corals, such as elkhorn coral (Acropora palmata). Elkhorn coral recovery has been isolated and patchy, but recently a “re-sheeting” phenomenon, in which elkhorn tissue grows over standing dead coral skeletons, was observed along the reefs in the Mexican Yucatán peninsula. Little is known about the ecological factors contributing to “re-sheeting,” but it is hypothesized that grazing from herbivores provides top-down control of algal growth and promotes coral recovery. The purpose of this study was to evaluate the status of elkhorn populations in Akumal, Mexico and determine if Diadema urchins or parrotfish populations are associated with higher elkhorn abundance and lower algal cover. To achieve this objective, we surveyed 12 spur and groove reef sites in Akumal, where re-sheeting was recently observed, and measured elkhorn coral and herbivore population metrics. We found that both herbivore groups are associated with increasing elkhorn coral presence and cover, and lower macroalgal cover. Additionally, we tested for sampling bias in counting Diadema urchins and found that a significant difference in urchins counts between paired day and night transects on shallow, high complexity reefs. Our results suggest that historically important herbivore groups may be contributing to the recovery of elkhorn coral in Akumal by facilitating tissue re-sheeting.

Ecosystem-based management efforts in coral reefs typically focus on reducing fishing pressure. However, independent of overfishing, tourism can degrade coral reefs through coastal development, as well as the physical presence of tourists within the ecosystem, the effects of which remain poorly understood. We combined a 3-year dataset on coral and algal cover with a more extensive survey of the benthic community to examine the effect of intensive tourism on a coral reef in Akumal Bay, Mexico. Results from our 3-year dataset indicated that near the peak snorkeling area in the bay, coral cover decreased by 79 % from summer 2011 through summer 2014, a period in which the number of monthly snorkelers increased by more than 400 %. Our summer 2013 survey of the benthic community between sites within a zone of dense snorkeler traffic versus site at a nearby control location revealed negative effects of intensive tourism on particular coral morphologies and on the abundance of herbivorous reef fishes. Our results suggest that uncontrolled tourism, including accelerating growth in the number of snorkelers, is likely contributing to the decline of the coral reef in Akumal Bay, where further expansions in tourism are planned. Indeed, the ecosystems threatened by overexploitation via tourism in the Mayan Riviera also form the basis for the regional tourism industry. Thus, long-term ecological monitoring coupled with the establishment and enforcement of regulations on tourism may be essential for the sustainability of coral reefs, as well as the socioeconomic benefits they provide in Mexico.

The Uvero-Punta Piedras section, a low-developed coastal strip located in the southern area of Quintana Roo, Mexico, is experiencing habitat degradation driven by unplanned population sprawl, unregulated tourism expansion and overfishing. The main objective of this study is to provide an environmental (coastal vegetation and coral reef condition) and socioeconomic (human population condition) baseline data of a poorly documented and weakly managed zone by the use of a set of rapid assessment methodologies, looking to assist the regional efforts to manage these coastal resources. To achieve this goal we used a series of surveying methods including remote sensing, geographic information systems and in situ land/underwater surveys, to allow a broad characterization of the resources' condition in the study zone. Results showed that reef habitat was dominated by macro-algae (61.2 ± 7.6%), followed by soft coral (gorgonians, 12.4 ± 4.1%), hard coral (8.2 ± 5.1%) and sponges (2.5 ± 1.3%). Zooanthids and tunicates represented less than 1% of the total; coral and macro algae estimates suggest a decline from records of 15 years ago. Highest fish densities were (144 ± 124 individuals/100 m2), while lowest were (83 ± 25 individuals/100 m2). The total average fish density recorded could also be reflecting a decrease trend in the reef community structure. The main economic activities in the area are fishing and land clearing. From December 2003, 22% (corresponding to 44 ha) of the total original vegetation cover in the studied area was deforested. By February 2007, the deforested area increased 4.4 ha more. Should this tendency continue, by 2025 it would only maintain 24% of its total coastal vegetation cover representing a huge habitat loss. The future of economic activities in these areas lie directly on the establishment of appropriate management strategies for the protection and conservation of the renowned biodiversity that this area comprises.