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Understanding the effects and benefits provided by the design and management of Marine Protected Areas (MPAs) is crucial for developing cost‐effective management actions. We characterized the management and design of no-take zone (NTZ) networks of eight Mexican Caribbean MPAs. To determine protection effectiveness, we followed a two-step approach. First, we evaluated the effect of the level of protection (NTZ, partial and unprotected areas), habitat structure and local human threats on four fish community metrics: total biomass, commercial fish biomass, mean trophic level and commercial fish mean size. If the protection afforded by the NTZ was significant, a second model was developed to evaluate design and management effectiveness. Total biomass, commercial fish biomass and mean trophic level were correlated significantly and positively with no-take protection; and, partially protected areas showed a significant and positive correlation with commercial fish biomass and mean trophic level. MPA age was the only significant and positive design and management characteristic that explained the variation in commercial fish biomass. This might be in part due to the suboptimal design of the MPA network that has mostly resulted from economic and social opportunities with little consideration for ecological guidelines and management capacities. Our findings suggest that to increase reef fish protection it would be necessary to include reef habitats with high coral cover and structural complexity inside NTZs. However, the effectiveness of an MPA network not only requires ecological considerations but also factors that include compliance, enforcement and true community participation to achieve greater benefits. Policymakers must ensure adequate design and management of MPAs in order to improve the effectiveness of marine resource protection, promoting both sustainable use and long-term biodiversity conservation.

Sea-level rise (SLR) is predicted to elevate water depths above coral reefs and to increase coastal wave exposure as ecological degradation limits vertical reef growth, but projections lack data on interactions between local rates of reef growth and sea level rise. Here we calculate the vertical growth potential of more than 200 tropical western Atlantic and Indian Ocean reefs, and compare these against recent and projected rates of SLR under different Representative Concentration Pathway (RCP) scenarios. Although many reefs retain accretion rates close to recent SLR trends, few will have the capacity to track SLR projections under RCP4.5 scenarios without sustained ecological recovery, and under RCP8.5 scenarios most reefs are predicted to experience mean water depth increases of more than 0.5 m by 2100. Coral cover strongly predicts reef capacity to track SLR, but threshold cover levels that will be necessary to prevent submergence are well above those observed on most reefs. Urgent action is thus needed to mitigate climate, sea-level and future ecological changes in order to limit the magnitude of future reef submergence.

The decline of reef‐building corals in conjunction with shifts to short‐lived opportunistic species has prompted concerns that Caribbean reef framework‐building capacity has substantially diminished. Restoring herbivore populations may be a potential driver of coral recovery; however, the impact of herbivores on coral calcification has been little studied. We performed an exclusion experiment to evaluate the impact of herbivory on Orbicella faveolata coral growth over 14 months. The experiment consisted of three treatments: full exclusion cages; half cage procedural controls; and uncaged control plates, each with small O. faveolata colonies. We found that herbivorous fish exclusion had a substantial impact on both macroalgal cover and coral growth. Fleshy macroalgae reached 50% cover within some exclusion cages, but were almost absent from uncaged control plates. Critically, O. faveolata calcification rates were suppressed by almost half within exclusion cages, with monthly coral growth negatively related to overgrowth by fleshy macroalgae. These findings highlight the importance of herbivorous fishes for coral growth and the detrimental impact of macroalgal proliferation in the Caribbean. Policy makers and local managers should consider measures to protect herbivorous fishes and reduce macroalgal proliferation to enable coral communities to continue to grow and function.

Long-term phase shifts from coral to macroalgal dominated reef systems are well documented in the Caribbean. Although the impact of coral diseases, climate change and other factors is acknowledged, major herbivore loss through disease and overfishing is often assigned a primary role. However, direct evidence for the link between herbivore abundance, macroalgal and coral cover is sparse, particularly over broad spatial scales. In this study we use a database of coral reef surveys performed at 85 sites along the Mesoamerican Reef of Mexico, Belize, Guatemala and Honduras, to examine potential ecological links by tracking site trajectories over the period 2005–2014. Despite the long-term reduction of herbivory capacity reported across the Caribbean, the Mesoamerican Reef region displayed relatively low macroalgal cover at the onset of the study. Subsequently, increasing fleshy macroalgal cover was pervasive. Herbivorous fish populations were not responsible for this trend as fleshy macroalgal cover change was not correlated with initial herbivorous fish biomass or change, and the majority of sites experienced increases in macroalgae browser biomass. This contrasts the coral reef top-down herbivore control paradigm and suggests the role of external factors in making environmental conditions more favourable for algae. Increasing macroalgal cover typically suppresses ecosystem services and leads to degraded reef systems. Consequently, policy makers and local coral reef managers should reassess the focus on herbivorous fish protection and consider complementary measures such as watershed management in order to arrest this trend.

Marine ecosystems globally have suffered habitat, biodiversity and function loss in response to human activity. Marine Protected Areas (MPAs) can limit extractive activities and enhance ecosystem resilience, but do not directly address external stressors. We surveyed 48 sites within seven MPAs and nearby unprotected areas to evaluate drivers of coral reef condition in the Mexican Caribbean. We found that local human activity limits protection effectiveness. Coral cover was positively related to protection characteristics, but was significantly lower at sites with elevated local human activity. Furthermore, we predict ongoing coastal development will reduce coral cover despite expanded protection within a regionwide MPA if an effective integrated coastal zone management strategy is not implemented. Policy makers must acknowledge the detrimental impact of uncontrolled coastal development and apply stringent construction and wastewater regulations in addition to marine protection.