Oceanography march 2007 a c r o s s t h e g l o b e , we are witnessing the decline of coral reef ecosystems. One relatively new factor contributing to this decline is the outbreak of destructive infectious diseases, especially on Caribbean reefs. As the Coral Disease Working Group of the Coral Reef Targeted Research Program, our research focuses on four priorities: (1) assessing the global prevalence of coral disease, (2) investigating the environmental drivers of disease, (3) identifying the pathogens that cause disease, and (4) evaluating the coral's ability to resist disease. Monitoring has revealed new coral-disease syndromes at each of four Global Environmental Fund Centers of Excellence: the Caribbean, the Philippines, Australia, and East Africa. Over the last 20 years, drastic (> 50 percent) loss of coral cover has occurred on the Yucatán Peninsula, even in pristine areas. Global surveys have revealed signifi cant levels of disease and disease outbreaks occurring not only in the Caribbean "hotspots," but also in sites throughout the Pacifi c and Indian Oceans. By monitoring coral disease, we will create a baseline and long-term data set that can be used to test specifi c hypotheses about how climate and anthropogenic drivers, such as decreasing water quality, threaten coral reef sustainability. One such hypothesis is that high-temperature anomalies drive outbreaks of disease by hindering the coral's ability to fi ght infection and by increasing the pathogens' virulence. We observed recurrent outbreaks following the warm summer months of two of the most damaging diseases in the Caribbean. In addition, we found that coral disease in the Great Barrier Reef correlated with warm temperature anomalies. In the Caribbean and Mediterranean Seas, virulence of known coral pathogens and the normal coral fl ora changed during high-temperature periods. Other stresses such as high nutrients and sedimentation may similarly alter the balance between the coral and its resident microbial fl ora.

Increasingly frequent severe coral bleaching is among the greatest threats to coral reefs posed by climate change. Global climate models (GCMs) project great spatial variation in the timing of annual severe bleaching (ASB) conditions; a point at which reefs are certain to change and recovery will be limited. However, previous model-resolution projections (~1 × 1°) are too coarse to inform conservation planning. To meet the need for higher-resolution projections, we generated statistically downscaled projections (4-km resolution) for all coral reefs; these projections reveal high local-scale variation in ASB. Timing of ASB varies >10 years in 71 of the 87 countries and territories with >500 km2 of reef area. Emissions scenario RCP4.5 represents lower emissions mid-century than will eventuate if pledges made following the 2015 Paris Climate Change Conference (COP21) become reality. These pledges do little to provide reefs with more time to adapt and acclimate prior to severe bleaching conditions occurring annually. RCP4.5 adds 11 years to the global average ASB timing when compared to RCP8.5; however, >75% of reefs still experience ASB before 2070 under RCP4.5. Coral reef futures clearly vary greatly among and within countries, indicating the projections warrant consideration in most reef areas during conservation and management planning.

Size‐specific mortality can determine whether coral transplants become successfully established in a reef rehabilitation effort. Presented here are results of a study of size‐specific mortality in laboratory‐cultured transplants, and the mediating effect of fusion on their survival and growth. Culturing seeded colonies for transplantation minimizes impacts to source reefs. This strategy provides an opportunity to enhance survival of a transplanted population by incorporating selected aspects of colonial modular biology, such as fusion, into the culture phase. Despite efforts to develop a completely field‐based method, settlement and early survival of juveniles of the scleractinian Pocillopora damicornis were much higher in laboratory aquaria than among those settled on reef substrate, highlighting the difficulty of direct seeding and justifying the higher effort involved in laboratory rearing. Juvenile colonies from four size cohorts (≤3 mm, 3.1–6 mm, 6.1–10 mm, and 10.1–29 mm), outplanted to a reef in August 1997, showed one‐year survival of 0%, 2.5%, 16.3%, and 47.5%, respectively, illustrating significant size‐specific mortality. Colony fusion resulted in lower 6‐mo mortality (unfused colonies: 34.5% ± 0.4%, fused pairs: 14.0% ± 2.5%, fused groups: 8.3% ± 4.8%; means ± 1 se), and chimeras of >2 fused colonies produced polyps faster. Tissue necrosis along fusing colony borders was observed between 8‐mo‐old colonies. This suggested a rejection response, though colonies fusing prior to this age remained stable for up to one year. A transition matrix revealed that fused colonies showed greater probability of growth to the next size class, while unfused colonies showed higher mortality and stasis. Growth trajectories based on transition probabilities suggested that fused colonies would reach reproductive size much earlier than unfused colonies. To test the hypothesis that larvae aggregatively settle to increase their chances of fusing, settlement patterns were determined in larvae of same‐ vs. mixed‐parent groups. Settled larvae were aggregatively distributed, with no difference in aggregation strength in larvae of same‐ vs. mixed‐parent groups. Results suggest a benefit of fusion to survival and growth within the first eight months in juvenile coral colonies. Fusion could be used as a strategy to obtain larger colonies faster, provided they remain stable over time. Laboratory seeding and rearing of juveniles to 10 mm provides a workable alternative to fragment transplantation in brooding coral species, and similar strategies may also be developed for spawning species.

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Coral diseases are taking an increasing toll on coral reef structure and biodiversity and are important indicators of declining health in the oceans. We implemented standardized coral disease surveys to pinpoint hotspots of coral disease, reveal vulnerable coral families and test hypotheses about climate drivers from 39 locations worldwide. We analyzed a 3 yr study of coral disease prevalence to identify links between disease and a range of covariates, including thermal anomalies (from satellite data), location and coral cover, using a Generalized Linear Mixed Model. Prevalence of unhealthy corals, i.e. those with signs of known diseases or with other signs of compromised health, exceeded 10% on many reefs and ranged to over 50% on some. Disease prevalence exceeded 10% on 20% of Caribbean reefs and 2.7% of Pacific reefs surveyed. Within the same coral families across oceans, prevalence of unhealthy colonies was higher and some diseases were more common at sites in the Caribbean than those in the Pacific. The effects of high disease prevalence are potentially extensive given that the most affected coral families, the acroporids, faviids and siderastreids, are among the major reef-builders at these sites. The poritids and agaricids stood out in the Caribbean as being the most resistant to disease, even though these families were abundant in our surveys. Regional warm temperature anomalies were strongly correlated with high disease prevalence. The levels of disease reported here will provide a much-needed local reference point against which to compare future change.