Top row from left to right: Campbell Thurman, Aric Bickel, Andrew Baker, Liv Williamson, Emily Corrigan, Brianna Fodor, Elyse Kochman. Middle row from left to right: Ross Cunning, Amparo Segurado, Marcus Wolf, Natalia Hurtado, Alain Duran, Valeria Pizarro, Margaret Miller, Christophe Noeztli. Bottom row left to right: Lindsey Condray, Melanie Warren, Hannah Lochan.

Top row from left to right: Campbell Thurman, Aric Bickel, Andrew Baker, Liv Williamson, Emily Corrigan, Brianna Fodor, Elyse Kochman. Middle row from left to right: Ross Cunning, Amparo Segurado, Marcus Wolf, Natalia Hurtado, Alain Duran, Valeria Pizarro, Margaret Miller, Christophe Noeztli. Bottom row left to right: Lindsey Condray, Melanie Warren, Hannah Lochan.

Last week, as Eleuthera basked in the brightness of the full moon, the Cape Eleuthera Institute welcomed an eclectic group of coral scientists and aquarists for our second annual Coral Breeding & Restoration Workshop. The program was led by Secore International and supported by The Nature Conservancy as a part of their Bahamas Coral Innovation Hub, as well as the Perry Institute for Marine Science. 

Excited to learn from these experts, aquarists from Minnesota Zoo, Aquarium of the Pacific, Avanqua Oceanográfic S.L., Ripley’s Aquarium of Canada, and Omaha's Henry Doorly Zoo and Aquarium, traveled from the United States, Canada, and Europe to participate in the twelve day workshop at CEI. 

Secore research director, Margaret Miller, demonstrating how the gamete jars will be fastened to the collectors.

Secore research director, Margaret Miller, demonstrating how the gamete jars will be fastened to the collectors.

A Day in the Coral Workshop 

On the first day, participants attended a Carribbean Coral Identification talk to help them properly identify Boulder Brain Coral (Colpophylia natans) and Mountainous Star Coral (Orbicella faveolata) ; the species we were most interested in collecting gamete bundles from.

This presentation was followed by a dive briefing to explain proper technique for placing “collectors” - or mesh cones - over coral colonies, as well as how to handle glass jars once filled sufficiently with gamete bundles. These skills would be employed during upcoming night dives.

Participating aquarists carry large trays of seeding units to CEI’s boat.

Participating aquarists carry large trays of seeding units to CEI’s boat.

The next day, all hands were on deck preparing Secore’s iconic seeding units, commonly referred to as “tetrapods”, for the arrival of coral larvae later on in the workshop. Over the years, Secore has gone through various seeding unit designs - experimenting with overall shape and groove placements to optimize larval settlement. Another way to encourage settlement is through biofilm. A few months ago, our resident coral researcher Valeria Pizzaro, from Perry Institute of Marine Sciences, submerged trays full of seeding units in our boathouse cut to accumulate bacterial biofilm. This step is crucial because bacterial communities emit cues to coral larvae, which attracts them and triggers settlement.

The coral team, consisting of workshop hosts, participants, and CEI interns, working together to deploy seeding units into Secore’s pools.

The coral team, consisting of workshop hosts, participants, and CEI interns, working together to deploy seeding units into Secore’s pools.

Once all of the conditioned seeding units were pulled out of the water and loaded onto the boat, the coral team strategically deployed them into structures resembling inflatable pools in the marina. The hexagonal pools were uniquely engineered by Secore to keep coral larvae contained, yet still allow for waterflow. In an assembly line fashion, some team-members carried trays to the floating dock, where others handed them down to divers, who in turn shuttled the seeding units to the pools. The marina was deemed an ideal “holding area” for coral larvae since the water quality closely resembles that of the sea, but is more protected from the elements. 

With the pools and seeding units in place, the anticipation for spawning grew stronger but was short-lived. The very next night, six distinct mountainous star coral colonies spawned, and roughly two million eggs and sperm were collected. As soon as divers returned to the boat, they mixed the contents of all of their jars into one container to initiate fertilization and optimize chances of cross-breeding. Collecting gamete bundles from as many different colonies as possible is key for encouraging genetic diversity so the team was content with their collection.

Around 2:30 am, fertilized eggs were transported and released into Secore’s pools for in situ rearing, and Cape Eleuthera Institute’s wet lab to begin ex situ rearing. The next day, mid-day, the fertilized eggs - now larvae - were observed through a microscope and seen “swimming”. This behavior indicated that they were progressing into pelagic planulae, and on the right track to eventually settling onto the prepared seeding units.

While most coral larvae were placed in the pools at the marina, others were kept in our wet lab to monitor their development. In the lab, the coral team is able to track, more or less, what is going on in the pools without interfering, and conduct additional research. 

Coral larvae swimming in a one centimeter-wide drop of water.

Coral larvae swimming in a one centimeter-wide drop of water.

Delving into Research 

In addition to the workshop participants, coral researchers from The University of Miami’s Coral Reef Futures Lab and Shedd Aquarium also joined the group. Their ongoing research focuses on the algal symbionts that live within the tissue of reef-building stony corals. Through photosynthesis, these symbionts provide their sessile coral hosts with vital nutrition. Under stressful conditions, like changes in seater pH and temperature, corals expel these symbionts in a process known as “coral bleaching” which, if prolonged,  can be fatal. However, certain symbionts are more tolerant of stressful conditions, and less likely to be expelled. 

Throughout the workshop, these researchers conducted experiments to test if newly settled coral recruits could be manipulated to take up thermally tolerant symbionts (Durusdinium trenchii) from the very beginning of their lives. Because D. trenchii has been found to help its coral hosts resist bleaching during high temperature stress, these researchers are investigating whether it could enhance the survival of juvenile corals in the face of climate change and ocean warming. 

“By rearing coral larvae in a relatively controlled environment like in the pools, Secore increases rates of settlement and survival compared to what we usually see in nature. The goal for our ongoing research is to determine whether seeding newly formed coral colonies with thermally tolerant symbionts can further increase their survivorship by making them more resilient to temperature stress.” - Liv Williamson, Ph.D. student at the University of Miami

In a few weeks, after the batch of coral recruits from this experiment have established symbiosis, they will be outplanted to local reefs and monitored over time for survival, growth, and symbiont community changes. If proven successful, this technique may be applied to more coral recruits in future breeding and restoration workshops. 

Dr. Ross Cunning (Shedd Aquarium) and Ph.D. student Liv Williamson (University of Miami) monitor temperature and light levels in one of the 8 experimental aquaria. Newly settled coral recruits will be added to each aquarium, where they will be exposed to different temperatures and symbiont availability treatments for several weeks.

Dr. Ross Cunning (Shedd Aquarium) and Ph.D. student Liv Williamson (University of Miami) monitor temperature and light levels in one of the 8 experimental aquaria. Newly settled coral recruits will be added to each aquarium, where they will be exposed to different temperatures and symbiont availability treatments for several weeks.

Workshop Wrap Up

Exactly one week after gamete bundles were collected from the wild, the coral team observed pelagic planulae begin to settle and metamorphose in the lab!

Three larval recruits are seen settled on substrate thanks to a Dino-Light digital microscope. Photo by Alain Duran.

Three larval recruits are seen settled on substrate thanks to a Dino-Light digital microscope. Photo by Alain Duran.

Approximately one week after that, these recruits began what will perhaps be their most crucial transformation: becoming primary polyps. Once a polyp, with fully formed tentacles and a mouth, they will be able to filter-feed and ingest photosynthetic symbionts. These nutrients will bolster their growth and eventually allow them to turn into colonies.

Multiple coral recruits now have a white rim - this is the newly formed skeleton. In addition, the little protuberances in the center of each settler will soon become tentacles surrounding the mouth. Photo by Alain Duran.

Multiple coral recruits now have a white rim - this is the newly formed skeleton. In addition, the little protuberances in the center of each settler will soon become tentacles surrounding the mouth. Photo by Alain Duran.

Once these settlers complete their transformation into true primary polyps, and once seeding units are seeded with juvenile colonies, the coral team will boat them out to nearby reefs and reintroduce these colonies into the wild. A subset of the seeding units will be monitored periodically to track the persistence of the seeding units and survivorship of the new polyps, though the very small size and slow growth rate of this species makes getting quantitative field data challenging.  

The Cape Eleuthera Institute is proud  to have been able to bring together such passionate people from around the world for the betterment of coral reefs. The Coral Breeding and Restoration Workshop is an incredible way to spread scientific knowledge, fieldwork strategy, and tangible solutions to help restore coral reefs near and far. “Many of these corals I had only seen in tanks so it was amazing getting to see them out on the reef. That being said, it was also very sobering because we inevitably saw newly dead or bleached colonies as well. This experience allowed me to see the whole picture, and highlighted the role aquariums may need to take in preserving coral reefs through “ark” type projects.” - Lindsey Condray, Aquarist at Omaha’s Henry Doorly Zoo and Aquarium.

 Thanks to the help of the 13 aquarists who participated in the workshop, we were able to rear about a million larvae in total, giving us all a little more hope for the reef ecosystems here in Eleuthera and the wider Caribbean. 

Make sure to follow along on our social media and subscribe to our newsletter, as we will be outplanting these colonies onto the reef very soon!