Envisioning a future for Caribbean coral reefs: lessons in resilience and collaboration

It’s not always easy for scientists in my field to think about the future. I study corals. These invertebrates are the architects of some of the most biodiverse ecosystems on the planet: tropical coral reefs. Corals’ symbiotic relationship with microscopic photosynthesizing algae provide them with the energy needed to build their skeletons, creating the three-dimensional structure of the reef that provides a colorful habitat for fish and other organisms.

However, the same relationship that enables corals to build these massive calcium carbonate structures is what puts them at risk due to rising temperatures. When water temperatures increase even just 1-2 degrees Celsius above the summer average, the symbiosis between coral and algae is disrupted in a phenomenon called coral bleaching. The coral animal expels its symbiotic partner, turns stark white, and is at risk of slowly starving to death if temperatures don’t return to normal. 

During the summer of 2023, I saw the effects of bleaching up close when my research sites in the Florida Keys experienced an unprecedented heatwave. Coral scientists use a heat stress metric called degree heating weeks (DHWs), which integrates both the amount of heat and how long it has persisted, to measure the amount of heat stress a reef has experienced. Usually, we start to see widespread coral mortality after about 8 DHWs. That summer, the Florida Keys accumulated over 20 DHWs.

My study species, Acropora cervicornis, also known as the staghorn coral, was one of the most severely affected. This species is used throughout the Florida Keys and the wider Caribbean for reef restoration due to its fast growth and branching morphology that allows for easy fragmentation in coral nurseries, where smaller fragments can be grown to larger sizes before being planted back on the reef. The widespread death of these corals throughout the region has been disastrous to these efforts. 

Of the 200 coral fragments I planted on two Florida reefs in October 2022, only three remain alive today. The death of my corals wasn’t just a setback for my research progress, but was also emotionally devastating. After all, I started my PhD because I wanted to do applied research that would benefit restoration practitioners actively working to improve conditions on Florida’s reefs. Seeing these precious coral outplants die within a few short months made me doubt whether the work I was doing would have the chance to make an impact at all. 

Unfortunately, many other researchers and restoration practitioners throughout the Caribbean and the rest of the world had similar experiences: record high temperatures in 2023 and 2024 triggered the fourth global coral bleaching event. Many staghorn corals in the Caribbean didn’t make it through back-to-back record heatwaves. This mass bleaching event showed us that ongoing coral restoration efforts aren’t sufficient to keep up with the immense pressures of climate change. 

If we want Caribbean coral reefs to survive, we need to start thinking about the future–envisioning that future has been the focus of my research this summer. Our lab organized a workshop at the Reef Futures Symposium in Mexico in December 2024, where we brought together researchers, restoration practitioners, and managers from throughout the Caribbean region to talk about the lessons we learned from our losses, and how we can work together to implement climate-smart restoration interventions in this region. We asked: how can we ensure that our science is being translated from the lab bench into more resilient restored reefs?

Over the course of three days, we exchanged thoughts and opinions on the kinds of advanced coral restoration interventions we should prioritize in the Caribbean. We discussed ideas ranging from assisted gene flow–in which humans move corals around the region to allow the exchange of genes between populations that are no longer naturally connected–to thermal preconditioning–which involves exposing corals to mildly elevated temperatures in hopes of “training” them to better tolerate future heatwaves.

We considered geographical and ecological contexts in which different approaches might be best suited and what kinds of barriers may stop them from being implemented. Additinally, we thought about how we can ensure knowledge of what works–and what doesn’t–can be shared throughout the region, coining the term One Caribbean: despite national borders, our reefs are intricately connected, and our approaches to restoring them must reflect that. 

On the final day of the workshop, we used consent-based decision making to rank the different restoration strategies we had discussed based on their risk and efficacy. As a result, interventions were grouped into one of four categories: 

1. Low risk, high efficacy: these interventions are ready to be implemented now, and include strategies such as managed breeding to maintain genetic diversity and adding grazers to reefs to control algae.
2. High risk, high efficacy: these interventions need additional work to address the risks involved with implementing them. Examples include assisted gene flow and artificially evolving algal symbionts to be more tolerant of higher temperatures.
3. Low risk, low efficacy: these interventions still require additional research to make them more effective at larger scales. This includes strategies such as feeding corals during marine heatwaves and thermal preconditioning.
4. High risk, low efficacy: these interventions should not be prioritized right now as they are still too risky. Examples include brightening clouds and chemically manipulating carbon dioxide in seawater.

Since the workshop, I have had the immense privilege of continuing to work with workshop planners and participants to develop materials to communicate our results to a variety of audiences. This has included a policy brief encouraging policymakers to develop regulatory structures that can support the kind of restoration work we need to prioritize by fast-tracking emergency permitting and allowing the ethical, traceable exchange of genetic material throughout the Caribbean region.

This summer, I am working on developing a framework for researchers and restoration practitioners to work together to get some of the most promising interventions on the ground and tested in real-world conditions. Collaborating with so many incredible people from different backgrounds and areas of expertise who are connected by a common goal has shown me that collaboration is the key to resilience. Working together, a future in which we ensured the persistence of Caribbean reefs is slowly coming into focus.

Jenna Dilworth is supported by the Gerald Bakus Graduate Fellowship in Marine and Environmental Biology.