The environmental, ecological, and socioeconomic impacts associated with extreme weather events and long-term ocean warming resulting from recurrent marine heatwaves (MHWs) have had significant consequences for marine and coastal ecosystems in Puerto Rico. Despite this, very little is known about how these impacts affect species composition, natural processes, resilience, and ecosystem functions and services. This can have important implications for the success of ecological restoration efforts. The goal of this novel research program at SAM is to enhance our understanding of the historical patterns of climate change in Puerto Rico, the Caribbean, and the tropical Atlantic to better comprehend their impacts on coastal and marine ecosystems, and the long-term consequences of climate change projections under various sustainability scenarios for the conservation and restoration of coastal ecosystems.

The first project developed by the SAM-CSR was titled “Runaway climate across the Wider Caribbean and Eastern Tropical Pacific in the Anthropocene: Threats to coral reef conservation, restoration, and social-ecological resilience”. This was a collaboration between Dr. Hernández and Yanina M. Rodríguez González, and it was recently published in the journal Atmosphere Vol. 16 (2025) and can be downloaded at https://doi.org/10.3390/atmos16050575. The results are both very revealing and concerning. MHWs are increasingly affecting tropical seas, causing recurrent coral bleaching and mortality in the Wider Caribbean (WC) and the Eastern Tropical Pacific (ETP). This leads to significant coral loss, reduced biodiversity, and impaired ecological functions. Climate models predict a worrying future for Latin American coral reefs, but downscaled projections for the WC and ETP remain limited. Understanding future regional temperature thresholds that threaten coral reefs and restoration efforts is critical. Our objectives included analyzing historical trends in July-August-September-October (JASO) temperature anomalies and exploring future projections at the subregional and country levels.

From 1940 to 2023, JASO air and ocean temperature anomalies showed significant increases. Projections indicate that even under the optimistic scenario 4.5, temperatures could exceed the threshold of +1.5°C in air temperature anomaly above pre-industrial levels by the 2040s and the threshold of +1.0°C in sea surface temperature (SST) anomaly above historical annual maximums by the 2030s, resulting in severe coral bleaching and mortality. The pessimistic business-as-usual scenario 8.5 suggests that conditions will become intolerable for coral conservation and restoration by 2030, with decadal warming trends far exceeding historical rates, under conditions unsustainable for corals. The immediate development of adaptive regional and local coral reef conservation and restoration plans, along with climate change adaptation and mitigation strategies, is essential to allow time for the optimistic scenarios to materialize.

A second important project is being completed by the SAM-CSR by Dr. Hernández under the title of “Increased marine heatwave impacts across the Caribbean Sea and the future of coral reefs”. Historical SST anomalies and degree heating weeks (DHW) data sets from 1985 to the present, generated by NOAA’s Coral Reef Watch Program, reveal significant trends in persistent MHWs across the Wider Caribbean region. Over the past few decades, there has been a marked increase in SST, with the frequency, duration, and intensity of MHWs rising significantly. This warming trend poses an acute threat to coral reef ecosystems, which are sensitive to temperature fluctuations. Climate models suggest increased annual mean DHW levels across the region ranging from about 25 to >40 annual mean DHWs by 2100, which indicate prolonged periods of thermal stress, leading to widespread coral bleaching and mass coral mortality events. The repercussions for coral reefs are profound, as these ecosystems provide essential services, including sustaining biodiversity, coastal protection, and economic benefits from tourism and fisheries. Looking ahead, regardless of projected IPCC optimistic scenario 4.5 or business-as-usual scenario 8.5, if current warming trends continue, the resilience of coral reefs may be compromised due to unbearable conditions for coral survival by the end of the century due to enhanced persistence of extreme heat, resulting in critical phase shifts in species composition and declines in biodiversity and ecological functions. Immediate and effective conservation strategies, alongside global efforts to mitigate extreme heat, are critical to safeguard these vital ecosystems from the escalating threat of marine heatwaves.

In addition, a third project entitled “Ecological restoration viability of degraded urban coral reefs: A case study from the Caribbean Sea under different projected climate change scenarios” is a joint project with SAM’s REef COnservation, Vitalization and Ecological Restoration Program (R.E.C.O.V.E.R.). It is aimed at developing coral demographic models parameterized with information on the demographic consequences of the 2023 and 2024 mass coral bleaching and mortality events, to project coral reef futures (2025-2050) under different sustainability scenarios and under different mass coral bleaching recurrence rates. Demographic modeling can provide paramount information to understand the potential consequences of future climate variation, but also to understand the critical importance of sustained coral restoration for the sustainability of viable coral populations, particularly in highly vulnerable shallow coral reef ecosystems which are vital for the protection of coastal infrastructure and life.

Another major project being developed by the SAM-CSR has been the monthly production of technical bulletin known as “Analysis of the Risks of Thermal Stress in Marine Ecosystems and Mass Coral Bleaching” since 2023. This document was produced between May and November of 2023 and 2024, during the warming period between the late Spring and early Fall, with the goal of documenting trends in sea surface temperature increases, accumulated DHWs, ocean heat content, El Niño and La Niña circulation patterns, and other oceanographic factors that could lead to coral bleaching in the Caribbean Basin and Puerto Rico. The first technical bulletin of 2025 was produced during June. Its main objective is to provide a Spanish-written summary of critical technical information regarding sea surface warming risks as a decision-making tool for government agencies, academia, non-governmental entities, environmental organizations, and the public across the Spanish-speaking Caribbean regarding marine ecosystem management and ecological restoration.