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Caribbean Spawning – Corals Keep Us Busy!

The coral spawning season is the busiest and most exhausting time of the year for our field staff. This year is even more challenging. To overcome pandemic restrictions, we started new partnerships, established new logistics, and cooperate with volunteers on-site. And finally, the corals did spawn!

Most corals release their egg and sperm bundles after sunset during mass spawning events. This coincidence allows for collecting spawn in huge quantities within a few days (broadcast spawners). For the teams on-site, this time is challenging and rewarding at once. They prepare gear and sample devices, set up the spawning lab and CRIBs (Coral Rearing In Situ Basins), review land-based rearing facilities, assemble teams for the night dives, and handle extended lab shifts. Additionally, this year they face another quite tricky yet crucial challenge: all tasks need to take place under pandemic regulations and precautions.

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Photos: title, coral embryos in a drop of water (Nicolas Rivas); spawning Orbicella cf faveolata (mountainous star coral)―left to the spawning one, there is a setting specimen, i.e. a coral that is preparing to release it's eggs and sperm bundles, which can be seen as yellowish dots within the polyps' mouths (Paul Selvaggio).

Usually, the night diving starts a few days before the predicted spawning window, making sure to capture that precious moment. Nature is not always that predictable, and no one wants to miss the one to few hours when the corals finally spawn. After a successful spawning dive, the lab is busy like a beehive, and everyone needs to know exactly what to do. After fertilization has taken place, the new coral babies start to grow, and the team is thrilled to monitor their development while taking care to provide the optimal growth conditions. Then, if all goes well, a new cohort of tiny corals is rising on the settlement substrates, waiting to be brought back into the wild.


A new partnership has been formed to restore the Florida Reef Tract―'the backyard' of our Science Director Margaret Miller: together with the University of Miami, NOAA-Southeast Fisheries Science Center, Biscayne National Park, and the Phillip and Patricia Frost Museum of Science thousands of egg and sperm bundles of three different coral species (Acropora palmata, Acropora cervicornis, and Orbicella faveolata) were collected a few weeks ago. All of them are endangered yet important reef-building coral species.

The majestic elkhorn corals (A. palmata), once abundant wave-breakers and coastal protectors in the shallow, have shrunken to very low numbers, making each remaining specimen a precious and cherished potential parent. Florida's reefs face various threats, lately the lethal SCTLD (Stony Coral Tissue Loss Disease) that has spread since 2014. It affects many coral species that have been relatively resilient so far, such as the mountainous star coral (O. faveolata).

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Photos: left, spawning Acropora cervicornis (staghorn coral; Nicolas Rivas); mid, happy intern diving in spawning 'snowstorm' & right, CRIB (Coral Rearing In Situ Basin) at Frost Science (Miles McGonigle).

After the collected eggs were fertilized, the larvae were placed into our CRIBs at Frost Science. Now the team on-site monitors the development of the freshly settled corals. Joyfully they are quite numerous. However, it will be a challenge to bring them back into the wild under pandemic boating restrictions. But we are confident that we will work it out― together with our partners, we were able to overcome any arising challenges during the last weeks!

And spawning season is not over in Florida. The next target species will be the boulder brain coral (Colpophillia natans) or the great star coral (Montastrea cavernosa). None of them have been cultured in Florida before, so the coming weeks are going to be exciting!


In Curaçao, several elkhorn coral colonies (A. palmata) spawned last month. Our team on-site, supported by volunteers and two dedicated students who already joined last year's spawning work, captured those precious egg and sperm bundles. Under the lead of Research Scientist Valerie Chamberland, the team set up an experiment to better understand this species' reproduction cycle and to discover particularly what role age may play for parental colonies in terms of reproduction success.

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Photo: close-up of buoyant egg-and-sperm bundles accumulating in the tip of a sample vial after collection (Ashley Lindstrom).

Our coral restoration research focuses on many aspects of the corals' life cycle and aims at optimizing growth conditions for baby corals that are raised for restoration. For instance, during the first month of this year's spawning season, a study has been initiated by Kelly Latijnhouwers, our Caribbean Restoration Coordinator, to find out the best growth conditions for the grooved brain coral (D. labyrinthiformis).

More species will spawn September through October, and there is no time to rest for our tireless team, which is already gearing up for more spawning dives!


At the Riviera Maya, the grooved brain corals (D. labyrinthiformis) spawned in July too. The team on-site that consists of our own Restoration Technician, Sandra Mendoza, students, partners from ECO Parc Xcaret, and Coralium (National Autonomous University of Mexico) was able to collect spawn of this vital reef-building species. Take a look at the picture with those delicate coral babies growing! Around 900 Seeding Units (baby corals on substrates) were produced. In the next months, they will be put back on the reefs around Puerto Morelos.

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Photos: left, growing babies of the grooved brain coral (D. labyrinthiformis); mid, spawning Pseudodiploria strigosa (symmetrical brain coral); right, spawning specimen of P. strigosa with SCTLD (all photos Sandra Mendoza).

One month later, on the 10th of August, the team collected egg and sperm bundles from symmetrical brain corals (Pseudodiploria strigosa). This is a species susceptible to the spreading SCTLD, which has reached the coast of Mexico two years ago. Sandra Mendoza noticed a coral affected by SCTLD but which was yet spawning―probably this can be considered the last breath before an imminent death. But there is also hope: the cultivated larvae seemed healthy and settled successfully. Now, the young corals are growing for a few weeks without any sign of the disease!

Implementation partner sites
In the Dominican Republic, our implementation partner FUNDEMAR witnessed coral spawning and collected egg and sperm bundles successfully. To date, they have already 'seeded' over 1,200 Seeding Units (substrates with growing baby corals on them), calling this event Baby Coralmania! The team under the lead of Rita Sellares is not only enthusiastic but also dedicated, highly skilled, and―quite important in these challenging times―a group of determined troubleshooters  (Interview with Sellares: COVID won't stop us).

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Photo: one of the over 1,200 seeded substrates with freshly settled corals (Seeding Units) that were put on the reef during the 'Baby Coralmania' in the DR. The tiny corals are not yet visible with the bare eye (FUNDEMAR).

For the team around Francesca Virdis, Reef Renewal Foundation Bonaire, the season's exciting period starts right now! For the very first time, they will collect coral spawn to propagate corals sexually. On top of that, they will allow the larvae to settle on SECORE substrates and raise them in CRIBs, before the baby corals are transferred to the reef. It's not an easy task to accomplish, and usually, at least one SECORE scientist would have been on-site to supervise this full run. But pandemic restrictions didn't allow our team to join. Nonetheless, we are confident that our digital coaching, the practice learned last year, and the Bonaire team's dedication will lead to a successful spawning season!

We will keep you updated―more news will follow soon!

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Photo: other reef creatures join the coral spawning nights like this colorful brittle star stalking on a O. cf faveolata and releasing its vibrant greenish eggs into the water column (Paul Selvaggio).

Meet our supporters

SECORE's lead partners are:

Omaha's Henry Doorly Zoo and Aquarium
California Academy of Science
The Builders Initiative

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