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Ocean warming is increasing the incidence, scale, and severity of global-scale coral bleaching and mortality, culminating in the third global coral bleaching event that occurred during record marine heatwaves of 2014-2017. While local effects of these events have been widely reported, the global implications remain unknown. Analysis of 15,066 reef surveys during 2014-2017 revealed that 80% of surveyed reefs experienced significant coral bleaching and 35% experienced significant coral mortality. The global extent of significant coral bleaching and mortality was assessed by extrapolating results from reef surveys using comprehensive remote-sensing data of regional heat stress. This model predicted that 51% of the world’s coral reefs suffered significant bleaching and 15% significant mortality, surpassing damage from any prior global bleaching event. These observations demonstrate that global warming’s widespread damage to coral reefs is accelerating and underscores the threat anthropogenic climate change poses for the irreversible transformation of these essential ecosystems.

Coral diseases acting synergistically with other environmental stressors are a growing problem for Caribbean reefs. Hard coral cover, coral traits, and coral diseases were examined from 1999 to 2021 for Akumal reef, located in the Northern Mexican Caribbean. The 45 recorded coral species were classified into life-history strategies: competitive, stress-tolerant, and weedy, associated with different framework-building capacities. Results indicate that cumulative impacts of coral diseases outbreaks in the last two decades, in synergy with the effects of coastal development and thermal stressors, have decreased significantly cover and abundance of major reef-building corals, shifting the dominance of the coral assemblage to species belonging to non-framework weedy life history strategy, corresponding to a low Reef Functional Index. Due to the relevant role of coral diseases in shaping coral assemblages, addressing current, and preventing future coral disease outbreaks through integrated management strategies, will be paramount to preserving physical functionality in Caribbean reefs.

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’.

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.

Tesis de Licenciatura

Resumen en español: "La diversidad biológica de la costa sur del estado de Quintana Roo se encuentra actualmente bajo presión debido a la incursión poblacional, la sobrepesca y la expansión del modelo masivodestructivo tradicional de la industria turística. La carencia de planes de desarrollo congruentes con los principios de sustentabilidad, sumada a la deficiencia en la puesta en práctica de los esquemas de planificación y ordenamiento ecológico territorial, ha propiciado un considerable deterioro ambiental. La reducción en la cobertura de vegetación de los humedales costeros y la alteración del equilibrio en comunidades marinas, como es el caso de los arrecifes coralinos, representan ejemplos característicos de dicho deterioro. En la región conocida como Costa Maya, al sur del Estado, se albergan aún algunas secciones litorales poco desarrolladas, principalmente cerca de áreas naturales protegidas. Tal es el caso de la sección Uvero-Punta Piedras, la cual colinda al norte con la Reserva de la Biósfera Sian Ka´an. No obstante, ya es posible observar los efectos negativos de las actividades humanas sobre estos hábitats. Por ello, el objeto de este estudio fue realizar una evaluación rápida en dicha sección, a fin de describir la condición en la cobertura de la vegetación costera y de la comunidad coralina del arrecife frontal, describiendo también la condición socioeconómica de la población que habita la zona. Para realizar la evaluación de los recursos naturales, fueron utilizadas imágenes de percepción remota de la zona, conocimiento de la gente local sobre el hábitat y estimaciones in situ. Se realizaron análisis cualitativos y cuantitativos mediante la integración de sistemas de información geográfica y uso de estadística multivariada. Para la evaluación socioeconómica se realizaron visitas a la población y se aplicaron encuestas. Se determinó que, de las 187 hectáreas que comprendió la sección terrestre del área de estudio, aproximadamente 23.5% de la cobertura de vegetación ya se encontraba en estado de denudación para finales del año 2003. Para principios del 2007, dicha cifra ascendió a casi 26%, siendo la tasa de cambio anual de la categoría de cobertura denudada (2003-2007) de 3.12% y la tasa anual de deforestación de -0.9%. De seguir esta tendencia de deforestación, para el año 2025 sólo se mantendría un 24.5% del total de este territorio cubierto por vegetación. La caracterización a nivel de grandes grupos morfo-estructurales del bentos arrecifal mostró una composición de 8% de corales pétreos, 12% corales blandos, 3% esponjas, 60% macroalgas y 17% bentos abiótico; la abundancia relativa de los grupos fue menor en la sección norte de la zona (sector I). La cobertura de corales pétreos ha sufrido una disminución de ~65% en los últimos 15 años, a partir de registros de cobertura de ~30% en 1993. Se encontraron 12 familias, 19 géneros y 31 especies de corales duros, con un promedio de 14 especies y 64 colonias por sitio. No se encontraron diferencias significativas de abundancia entre arrecifes. Agaricia agaricites, Siderastrea siderea y Porites astreoides fueron las especies más abundantes. En general, los corales revelaron una condición saludable; la mayor parte de las colonias enfermas o con blanqueamiento fue encontrada en los sectores III y IV. Se registraron 35 familias, 56 géneros y 98 especies de peces arrecifales, con un promedio de 24 especies y 150 individuos por sitio. Las familias con especies más abundantes fueron Haemulidae, Acanthuridae y Labridae. En promedio, se registró una densidad de 65 individuos por cada 100 m2. No se encontraron diferencias significativas en abundancia entre los sectores arrecifales estudiados. Este grupo ha sufrido una disminución de ~75% en sus volúmenes por causa de la pesca intensiva y la disminución en la cobertura de coral, partiendo de una densidad de 263 individuos/100 m2 reportada en 1993. Se consiguió entrevistar a 25 personas en la zona, de un total estimado de 70, permitiendo describir a una población socioeconómica y culturalmente compleja, con opiniones y expectativas diversas relativas al tipo de desarrollo turístico que será instituido y al nivel de participación de la gente local en el mismo. El crecimiento de esta población, así como el uso que le da al suelo y a los recursos naturales, requieren de urgentes medidas de regulación y planificación, a fin de evitar que la degradación del hábitat constituya la principal causa de obstrucción a opciones de desarrollo futuro. Así, resulta imperante la institución de programas de conservación y monitoreo de los recursos naturales aún presentes. Muchos de los resultados obtenidos pueden ser utilizados como conocimiento de base para toma de decisión y manejo en la zona. Esta información busca ser útil y contribuir al desarrollo sustentable, al beneficio de los habitantes locales y a la planificación de espacios inteligentes donde se conjunten prudentemente las actividades de recreación y conservación. "