Nursery-raised corals survived the Caribbean's worst bleaching event in decades at twice the rate of wild reefs

Reporting for this article draws on research and programme documentation from Fundación Dominicana de Estudios Marinos (FUNDEMAR) and SECORE International.

Key Points

✓ Young corals raised through FUNDEMAR's nursery programme suffered half the bleaching losses of surrounding wild reef during the Caribbean's catastrophic 2023 heat event — suggesting that the genetic diversity built into sexually reproduced coral populations may produce individuals better equipped to survive warming seas.
✓ FUNDEMAR ran five floating nursery structures simultaneously in 2023 — the largest single Coral Seeding operation ever recorded — and has increased production by 1,000% over five years, with more than 40,000 substrate units outplanted to degraded reef since 2019.
✓ Among the eight species FUNDEMAR has successfully cultivated is Pillar coral (Dendrogyra cylindrus), one of the Caribbean's most ecologically significant reef builders and one of the species most devastated by Stony Coral Tissue Loss Disease. Very few restoration programmes globally have managed to breed it reliably.
✓ FUNDEMAR has transitioned from programme participant to regional trainer, now building coral nursery capacity across multiple Caribbean nations — and organisations entering the network start with seven years of hard-won breeding knowledge already built in.

In the second half of 2023, a heat wave spread across the Caribbean and began killing coral. Water temperatures climbed beyond what the reefs could absorb, and bleaching — the stress response that leaves coral white, weakened, and vulnerable to death — spread through populations that had already been battered by years of disease. Many colonies died. But when researchers from the Fundación Dominicana de Estudios Marinos went back to monitor their restoration sites, they found something worth paying attention to: the young corals they had raised in floating nurseries and transplanted onto degraded reef showed half the bleaching losses of the surrounding wild colonies.

That result didn't arrive by accident. It came at the end of seven years of work by FUNDEMAR — a Dominican marine research organisation — developing a coral breeding programme from scratch, in collaboration with SECORE International. SECORE's Coral Seeding method takes advantage of corals' natural spawning events to produce genetically diverse larvae in large numbers. The scale FUNDEMAR has now reached — five floating nurseries operating simultaneously, production up 1,000% from where it started — represents both a technical achievement and a serious attempt to answer a question the restoration sector has long struggled to resolve: whether raising corals in nurseries can ever match the pace at which the ocean is losing them.

This decade is widely considered decisive for the fate of coral reefs. Stony Coral Tissue Loss Disease has torn through Caribbean species over the past several years, hitting those that had shown resistance to other pressures. The bleaching event of 2023 compounded losses that were already severe. The question is no longer whether conventional conservation is adequate — it clearly isn't — but what scaled, technically sophisticated intervention actually looks like in practice.

What survives and what doesn't

The Coral Seeding method that underpins FUNDEMAR's programme works differently from the fragmentation approaches that dominate most reef restoration. Fragmentation — clipping branches from existing colonies and growing them out — is faster to establish, but it reproduces the same genetic material each time. When a disease or thermal event targets a particular genotype, an entire nursery built from one parent colony can be wiped out.

Coral Seeding collects eggs and sperm during natural spawning events, fertilises them, and raises the resulting larvae through floating nursery structures before outplanting onto degraded reef. Every recruit is genetically unique. That distinction matters most during exactly the kind of event the Caribbean experienced in 2023. When FUNDEMAR's monitoring teams compared their outplanted sites with adjacent natural reef, the nursery-raised corals showed consistently lower bleaching rates. The leading explanation involves the range of thermal tolerance traits distributed across a genetically diverse population — some individuals carry genetic combinations that hold up better under heat stress. In a wild reef depleted by disease, those variants may already have been lost. In a nursery-raised cohort, they are represented from the start.

How Coral Seeding Works

Most coral restoration programmes work by clipping fragments from existing colonies and growing them out. This produces corals quickly, but every fragment is genetically identical to its parent — making nurseries vulnerable to any disease or heat event that targets that genetic line.

SECORE International's Coral Seeding method begins during natural coral spawning events, when colonies release eggs and sperm into the water. Researchers collect these, fertilise them, and raise the resulting larvae in floating nursery structures known as Coral Rearing In-situ Basins (CRIBs). Once large enough, the young corals are attached to substrate units and transplanted onto degraded reef.

Because each larva represents a unique genetic combination of two parent colonies, the resulting population carries a range of inherited traits — including, potentially, varying tolerance to heat stress. This diversity is what FUNDEMAR's monitoring data from 2023 suggests may be making the difference.

SECORE's research pipeline is now working to formalise this further, identifying parent colonies with documented thermal resilience and introducing them into the breeding programme as that science develops. The goal is a pipeline that runs from basic reproductive biology through to outplanted recruits with known stress-tolerance profiles — something that has been technically out of reach until very recently.

Rita Sellares, FUNDEMAR's Executive Director, has tracked the programme's trajectory across all of it. "Since 2019, we have been able to outplant over 40,000 coral substrates in total, each with several tiny corals growing on them, to degraded reef areas," she explains. At current production rates, the programme now expects to contribute 20,000 new substrates annually — and it is that output, combined with what the 2023 monitoring data revealed about their survival, that has drawn other Caribbean organisations to seek training from FUNDEMAR's team.

The coral almost nobody can breed

Among the eight species FUNDEMAR has brought through its programme is Dendrogyra cylindrus, the Pillar coral. On a healthy Caribbean reef, Pillar corals are among the most visually distinctive structures present — tall, finger-like columns that can reach two metres, providing the kind of vertical complexity that smaller organisms depend on for habitat. They are also among the species most comprehensively devastated by Stony Coral Tissue Loss Disease, which has reduced Pillar coral populations across much of the Caribbean to fragments of what existed a decade ago. Breeding them in controlled conditions has eluded most programmes that have attempted it.

The difficulty is in the detail. Dendrogyra cylindrus larvae are sensitive to water quality and temperature conditions in ways that shift between spawning events and between sites. There is no fixed protocol that works reliably everywhere. Success depends on close observation, adaptive adjustment, and accumulated site-specific knowledge that takes years to develop. SECORE's training model is built around this reality — partners spend time at SECORE facilities in Mexico and Curaçao, then return to their home waters and begin the process of learning what works for their reefs, their species, and their local conditions.

FUNDEMAR's success with Pillar coral is the product of that accumulation. Seven years of spawning events, trial outplanting, bleaching surveys, and species-by-species refinement have produced a team that now holds practical knowledge about Caribbean coral reproduction that exists nowhere else in the region at comparable scale. The challenge ahead is not whether that knowledge is real — the 2023 data confirmed it is — but how quickly it can be transferred to the organisations that need it before the window for meaningful intervention narrows further.

Teaching the region what took seven years to learn

FUNDEMAR is expanding its staff, enlarging its facilities, and now running training for organisations across multiple Caribbean nations. The shift from programme participant to regional trainer is the transition SECORE built its implementation model around: each organisation that reaches operational maturity becomes a node for spreading capacity outward, without requiring every new programme to rebuild the knowledge base from scratch.

Aric Bickel, SECORE's Director of Technology and Implementation, described the scale of what FUNDEMAR has become. "In just five years, FUNDEMAR has grown their Coral Seeding programme from the ground up to probably the largest in the world," he noted, adding that the next phase involves FUNDEMAR not only continuing to scale their own coral output but significantly increasing the number of groups they train to conduct this work across the region.

For the Caribbean — where the compounding of disease, bleaching, and cumulative human pressures has left reef systems in the worst condition in recorded history — the pace of that expansion will matter as much as the quality of what gets built. The organisations now entering SECORE's network through FUNDEMAR's training will start somewhere very different from where FUNDEMAR started in 2017: with a proven method, a tested species list that includes Pillar coral, and monitoring data from the region's worst recent bleaching event showing what a nursery-raised reef can survive.

By the Numbers

2×

Survival rate of nursery-raised corals versus wild reef during 2023 bleaching event

40,000+

Coral substrate units outplanted to degraded reef since 2019

1,000%

Production increase over five years of programme development

20,000

New coral substrates contributed annually at current production rate

Coral species successfully cultivated, including the rarely-bred Pillar coral

Floating nursery structures operated simultaneously in 2023 — the largest Coral Seeding operation ever recorded

Frequently Asked Questions

Why did nursery-raised corals survive bleaching better than wild ones?

Because each coral raised through the Coral Seeding method is genetically unique — the product of two parent colonies combining during natural spawning. This produces a population with a wide range of inherited traits, including varying degrees of heat tolerance. When bleaching conditions arrive, some individuals in a genetically diverse group are likely to carry combinations that hold up better under stress. In a wild reef already depleted by disease, those heat-tolerant variants may have been lost. In a nursery-raised cohort, they are present from the outset.

How is Coral Seeding different from standard reef restoration?

Most reef restoration programmes use fragmentation — clipping branches from existing colonies and growing them out. It is effective and fast to establish, but every fragment is genetically identical to its parent, making nurseries vulnerable to any disease or temperature event that affects that genetic line. Coral Seeding starts from eggs and sperm collected during natural spawning, raising larvae that are genetically distinct. The method takes longer to produce mature corals but builds in the diversity that fragmentation cannot.

Why is Pillar coral so significant — and so difficult to breed?

Dendrogyra cylindrus, the Pillar coral, provides the kind of tall, complex vertical structure that many Caribbean reef organisms depend on for habitat. Stony Coral Tissue Loss Disease has devastated its populations across the region over the past decade. Breeding it in controlled conditions is difficult because the larvae are sensitive to water quality and temperature in ways that vary between sites and spawning events — there is no fixed protocol that works everywhere, and success requires years of site-specific observation and adjustment. FUNDEMAR is one of very few programmes globally to have achieved it reliably.

How does FUNDEMAR's training programme work?

FUNDEMAR now trains organisations from multiple Caribbean nations in the Coral Seeding method, following the model developed by SECORE International: organisations that reach operational maturity become regional nodes for spreading capacity to others. Crucially, groups entering the network through FUNDEMAR's training begin with seven years of accumulated knowledge — tested species lists, proven protocols, and monitoring data from the 2023 bleaching event — rather than having to develop that understanding from scratch.

What is the broader significance of FUNDEMAR's work for Caribbean reefs?

Caribbean reef systems are in the worst condition in recorded history, following decades of compounding pressures — pollution, disease, bleaching, and physical damage. FUNDEMAR's programme represents one of the most credible attempts to demonstrate that restoration at meaningful scale is achievable, and that genetically diverse, nursery-raised populations can survive conditions that are eliminating wild reef. The 2023 monitoring results suggest the approach is working. The question now is whether the network of trained organisations can expand quickly enough for the difference to matter at a reef-wide scale.