Coral reefs are the most productive marine ecosystems on earth, providing habitat and resources for most of the ocean's species, as well as essential ecosystem services to costal human communities. But the future of coral ecosystems is severely threatened by local factors such as habitat destruction, pollution, and overfishing, as well as global factors associated with fossil fuel use, including increased oceanic surface temperatures, sea-level rise, and ocean acidification. Marine reserves and other conservation zones can promote ecosystem resilience by providing protections from localized threats and serving as a reservoir for marine communities. To assess the effectiveness of one marine reserve, the South Water Caye Marine Reserve in Belize, we assessed the health of coral reefs at five separate sites: one located outside the reserve, two located within a "general use" zone inside the reserve that allows fishing with some restrictions, and two located within a "conservation zone" inside the reserve with a complete ban on fishing. To assess the health of these reefs, we established four snorkeling transects at each site and recorded three aspects of coral ecosystem health: the herbivory rate of damselfish measured in bites per minute, the color or bleaching-level of stony coral measured using CoralWatch color-matching cards, and the overall coverage and species diversity of stony coral using five 1m x 1m quadrants per transect. We then compared the average or median value of these measures across sites using ANOVA or the nonparametric Kruskal-Wallis test, followed by pairwise Turkey or Wilcox Rank Sum tests, respectively. We found that the reef site located outside the marine reserve exhibited statistically worse outcomes in two of the three measures of ecosystem health, including higher rates of herbivory indicative of increased algal cover, and lower percentages of hard coral coverage and species diversity indicative or coral loss. All sites exhibited coral that were generally healthy based on median coloration, which did not differ across any of the sites. Although the two sites within the conservation zone generally exhibited the best measures of ecosystem health, including greater coral coverage and species diversity, these measures were not statistically different from the two sites found within the general use zone. Our results suggest that there is a gradual decline in coral ecosystem quality based on the level of protection in the South Water Caye area, and support the effectiveness of marine reserves in limiting declines in coral ecosystems due to localized threats.
