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Coral reefs are among the world’s most endangered ecosystems. Coral mortality can result from ocean warming or other climate-related events such as coral bleaching and intense hurricanes. While resilient coral reefs can recover from these impacts as has been documented in coral reefs throughout the tropical Indo-Pacific, no similar reef-wide recovery has ever been reported for the Caribbean. Climate change-related coral mortality is unavoidable, but local management actions can improve conditions for regrowth and for the establishment of juvenile corals thereby enhancing the recovery resilience of these ecosystems. Previous research has determined that coral reefs with sufficient herbivory limit macroalgae and improve conditions for coral recruitment and regrowth. Management that reduces algal abundance increases the recovery potential for both juvenile and adult corals on reefs. Every other year on the island of Bonaire, Dutch Caribbean, we quantified patterns of distribution and abundance of reef fish, coral, algae, and juvenile corals along replicate fixed transects at 10 m depth at multiple sites from 2003 to 2017. Beginning with our first exploratory study in 2002 until 2007 coral was abundant (45% cover) and macroalgae were rare (6% cover). Consecutive disturbances, beginning with Hurricane Omar in October 2008 and a coral bleaching event in October 2010, resulted in a 22% decline in coral cover and a sharp threefold increase in macroalgal cover to 18%. Juvenile coral densities declined to about half of their previous abundance. Herbivorous parrotfishes had been declining in abundance but stabilized around 2010, the year fish traps were phased out and fishing for parrotfish was banned. The average parrotfish biomass from 2010 to 2017 was more than twice that reported for coral reefs of the Eastern Caribbean. During this same period, macroalgae declined and both juvenile coral density and total adult coral cover returned to pre-hurricane and bleaching levels. To our knowledge, this is the first example of a resilient Caribbean coral reef ecosystem that fully recovered from severe climate-related mortality events.

Marine protected areas (MPAs) form the cornerstone of marine conservation. Identifying which factors contribute to their success or failure is crucial considering the international conservation targets for 2020 and the limited funds generally available for marine conservation. We identified common factors of success and/or failure of MPA effectiveness using peer-reviewed publications and first-hand expert knowledge for 27 case studies around the world. We found that stakeholder engagement was considered to be the most important factor affecting MPA success, and equally, its absence, was the most important factor influencing failure. Conversely, while some factors were identified as critical for success, their absence was not considered a driver of failure, and vice versa. This mismatch provided the impetus for considering these factors more critically. Bearing in mind that most MPAs have multiple objectives, including non-biological, this highlights the need for the development and adoption of standardized effectiveness metrics, besides biological considerations, to measure factors contributing to the success or failure of MPAs to reach their objectives. Considering our conclusions, we suggest the development of specific protocols for the assessment of stakeholder engagement, the role of leadership, the capacity of enforcement and compliance with MPAs objectives. Moreover, factors defining the success and failure of MPAs should be assessed not only by technical experts and the relevant authorities, but also by other stakeholder groups whose compliance is critical for the successful functioning of an MPA. These factors should be considered along with appropriate ecological, social, and economic data and then incorporated into adaptive management to improve MPA effectiveness.

Global climate change and localized anthropogenic stressors are driving rapid declines in coral reef health. In vitro experiments have been fundamental in providing insight into how reef organisms will potentially respond to future climates. However, such experiments are inevitably limited in their ability to reproduce the complex interactions that govern reef systems. Studies examining coral communities that already persist under naturally-occurring extreme and marginal physicochemical conditions have therefore become increasingly popular to advance ecosystem scale predictions of future reef form and function, although no single site provides a perfect analog to future reefs. Here we review the current state of knowledge that exists on the distribution of corals in marginal and extreme environments, and geographic sites at the latitudinal extremes of reef growth, as well as a variety of shallow reef systems and reef-neighboring environments (including upwelling and CO2 vent sites). We also conduct a synthesis of the abiotic data that have been collected at these systems, to provide the first collective assessment on the range of extreme conditions under which corals currently persist. We use the review and data synthesis to increase our understanding of the biological and ecological mechanisms that facilitate survival and success under sub-optimal physicochemical conditions. This comprehensive assessment can begin to: (i) highlight the extent of extreme abiotic scenarios under which corals can persist, (ii) explore whether there are commonalities in coral taxa able to persist in such extremes, (iii) provide evidence for key mechanisms required to support survival and/or persistence under sub-optimal environmental conditions, and (iv) evaluate the potential of current sub-optimal coral environments to act as potential refugia under changing environmental conditions. Such a collective approach is critical to better understand the future survival of corals in our changing environment. We finally outline priority areas for future research on extreme and marginal coral environments, and discuss the additional management options they may provide for corals through refuge or by providing genetic stocks of stress tolerant corals to support proactive management strategies.

Coral reefs are subjected globally to a variety of natural and anthropogenic stressors that often act synergistically. Today, reversing ongoing and future coral reef degradation presents significant challenges and countering this negative trend will take considerable efforts and investments. Scientific knowledge can inform and guide the requisite decision-making process and offer practical solutions to the problem of protection as the effects of climate change exacerbate. However, implementation of solutions presently lags far behind the pace required to reverse global declines, and there is a need for an urgent and significant step-up in the extent and range of strategies being implemented. In this paper, we consider scientific frontiers in natural and social science research that can help build stronger support for reef management and improve the efficacy of interventions. We cover various areas including: (1) enhancing the case for reef conservation and management, (2) dealing with local stressors on reefs, (3) addressing global climate change impacts, (4) and reviewing various approaches to the governance of coral reefs. In sum, we consider scientific frontiers in natural and social science that will require further attention in coming years as managers’ work towards building stronger support for reef management and improve the efficacy of local interventions.