Bonaire’s coral reefs are facing unprecedented challenges, from the rapid spread of Stony Coral Tissue Loss Disease (SCTLD) to the devastating impacts of mass bleaching events driven by record-high ocean temperatures. Reef Renewal Bonaire is tackling these threats head-on through innovative restoration techniques like selective propagation, coral breeding, and mitigation. By propagating and outplanting resilient coral strains, we aim to safeguard the genetic diversity and ecological integrity of Bonaire’s reefs, buying time for these critical ecosystems to adapt and survive in a changing climate.
Our efforts to monitor resilient populations, mitigate the impacts of rising temperatures, and respond during emergency weather events is made possible thanks to support from Bloomberg Philanthropies.
How We’re Responding
Monitoring Wild and Nursery Populations
Propagating Resilient Corals
Coral Breeding
Mitigating Impacts
Coral Bleaching on Bonaire
South Caribbean reefs have experienced unprecedented bleaching in recent years, driven by record-breaking ocean temperatures in 2023 and 2024—the two hottest consecutive years on record (NOAA Coral Reef Watch).
In Bonaire, over 80% of corals were affected by thermal stress in 2023, a sharp increase from just 25% in 2016 (Eckrich et al., 2024). This widespread bleaching impacts nearly every coral species on the island, weakening our marine ecosystem as a whole and leaving corals more vulnerable to disease and stress-related mortality.
The Arrival of Stony Coral Tissue Loss Disease (SCTLD)
Stony Coral Tissue Loss Disease (SCTLD) is a fast-acting pathogen that causes rapid tissue loss in many coral species in the Caribbean. Since the confirmation of SCTLD on Bonaire’s reefs in March 2023, the disease has spread rapidly, affecting 9 species of reef-building corals on the island.
Corals infected with SCTLD can lose large amounts of tissue within weeks, leaving them vulnerable to further stress and mortality. When paired with high ocean temperatures, its impact on Bonaire coral populations has been nothing short of devastating.
Our Actions
Monitoring Nurseries and Wild Populations
Our team routinely collects coral health data in our nurseries to assess how different genotypes and species respond to stressors. We also survey wild populations around the island to identify colonies that exhibit tolerance to elevated ocean temperatures and the spread of disease. Resilient corals are identified, tagged, and added to our nurseries, where they can be propagated and later outplanted back to the reef to strengthen vulnerable populations.
Monitoring becomes especially crucial during peak bleaching seasons or after the emergence of a new coral disease. For example, in November 2024, when water temperatures reached an all-time high, our team dedicated over 150 hours surveying over 25 dive sites to identify heat-tolerant colonies. These surveys allow us to pinpoint corals that can withstand extreme conditions, forming the foundation for our selective propagation and breeding programs.
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Propagating Resilient Corals
Once identified through monitoring efforts, corals that exhibit tolerance to extreme temperatures or disease are carefully harvested and transferred to our nurseries for propagation. Here, resilient genotypes are fragmented and grown into larger colonies, before being outplanted on the reef.
This approach, known as selective propagation, strengthens coral populations at the biological level. By outplanting these resilient corals back onto the reef, we aim to bolster the genetic diversity and abundance of vulnerable species, making them better equipped to endure future environmental stressors. From fragging to outplanting, each step in this process contributes to creating stronger, more resilient coral populations.
Breeding Corals
Coral breeding is a vital tool in restoration, enabling us to produce new generations of coral that are better equipped to withstand environmental stressors. This process begins with coral spawning, when sperm and egg bundles are collected from spawning colonies during a few nights each year. However, as populations of key species decline due to disease and bleaching, identifying target colonies and observing spawning becomes increasingly challenging.
To address this, we’ve expanded monitoring efforts around the predicted spawning windows of species like boulder, symmetrical, and grooved brain corals, as well as branching staghorn and elkhorn corals. These efforts are critical, as recent research we contributed to showed that young corals produced via breeding exhibit greater tolerance to bleaching than their wild counterparts (Miller et al., 2024).
Mitigation Strategies
The goal of mitigation is to reduce the stress that corals experience in our nurseries and outplanting sites, especially during extreme environmental events or vulnerable growth phases. Following 2023’s severe bleaching event, and in preparation for the 2024 bleaching season, we introduced shading structures to protect nursery corals from high temperatures and intense UV exposure. During the 2024 bleaching period, we also relocated nurseries with particularly vulnerable species, such as boulder and brain corals, to deeper, cooler sections of reef.
When it comes to outplanting, timing and location are everything. We strategically select restoration sites based on the most favorable conditions and focus on outplanting during cooler months of the year, to minimize stress on newly planted fragments.
Read more about shading and relocation efforts in our blog post: Shading Bonaire’s Corals: An Innovative Approach to Bleaching Mitigation.
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Safeguarding Diversity in our Gene Bank
As part of our mitigation strategy, we maintain a gene bank nursery to safeguard genetic diversity and protect against the loss of critical coral species. Currently, we propagate over 140 genotypes (genetic strains) in nurseries around the island. Representative samples of each genotype are preserved in the gene bank, where they can be monitored and protected year-round. This strategy reduces the risk of losing entire genotypes or species to threats like severe storms or disease outbreaks.
While diversifying the genotypes we propagate is essential, prioritizing the most vulnerable species is equally important. After SCTLD was introduced in early 2023, we added 4 species to our inventory, all especially susceptible to the disease: elliptical star coral (Dichoesina stokesii), pillar coral (Dendrogyra cylindrus), maze coral (Meandrina meandrites), and symmetrical brain coral (Pseudodiploria strigosa). Colonies were harvested from areas of high impact, indicating a level of tolerance to the disease. After late 2023’s mass bleaching event, another 5 vulnerable species were added to our nursery and gene bank.
Our efforts to monitor resilient populations, mitigate the impacts of rising temperatures, and respond during emergency weather events is made possible thanks to support from Bloomberg Philanthropies.
