A Firsthand Account of Coral Restoration in the Eastern Dominican Republic

Coral Conservation in Context

Coral reefs are the planet’s most bio-diverse ecosystems and are critical to maintaining the health of our oceans, and across the world they are dying. Corals first occurred on our planet some 500 million years ago, and have become entirely extinct several times, with millions of years lapsing between periods of their re-occurrence. In addition to being beautiful, coral ecosystems provide food for millions, buffer coastal communities against storm surge, and host unmatched biodiversity that could well hold the solutions to some of people’s greatest concerns, from climate change to cancer. Coral reefs also help maintain the health of surrounding mangroves, sea grass beds, and other coastal and marine habitats that work as one, interconnected ecosystem. Sadly, the ocean has become an ecosystem that is changing and being degraded more rapidly than our body of knowledge is growing, and so it is difficult to know what we stand to lose, and even what we have lost already. When we fail to set a consistent bar for what constitutes a healthy reef, social amnesia known as a “shifting ecological baseline” keeps lowering the bar a bit more every generation until we end up settling for what amounts to dead ocean, dominated by jellyfish, sponges and other primitive, opportunistic species. As in much of the Caribbean, the Dominican Republic’s coral reefs are already just a shadow of what they were in the 1960’s and are today unrecognizable from what they looked like even a mere decade ago, with only around 10% of their coral cover remaining. There are very few fish, especially large ones, and in general, one misses the biodiversity still seen in other less impacted areas of the Caribbean, such as in far southern islands like Trinidad and Tobago.

Incredibly, the largest structure ever created by living organisms on planet Earth is the Great Barrier Reef – a long and broad coral matrix that borders northeast Australia, extending from as far South as Brisbane to as far North as the Torres Strait. An area the size of Japan, the Great Barrier Reef, or GBR for short, is entirely composed of scleractinian, or stony corals made of hard, calcium carbonateskeletons. Soft corals are also present in the GBR and wider South Pacific but do not build reefs. Nevertheless, soft corals make reefs like Taveuni Fiji’s Rainbow Reef famous for their beauty as dive sites. Above Australia is a vast area known as the Coral Triangle which encompasses most of Indonesia and is home to the highest diversity of marine life that can be found on our blue planet.

Coral reefs occur throughout the tropics, primarily in nutrient poor, clear, shallow coastal waters, though some coral species can also be found at great depths and in cool, murky waters, such as in the Amazon River Delta where a deep-water reef was recently discovered. In comparison to the more accessible coastal reefs that suffer impacts like coastal run-off and erosion, deep sea corals are somewhat more protected, but are nonetheless being destroyed by dredging, deep sea trawling, plastic pollution, coral harvesting, and changing ocean temperatures. The second largest coral reef in the world is the Meso-American Reef, which extends along the southernmost edge of Mexico’s Yucatan Peninsula. Further North, in the Caribbean Sea, coral reefs are sparse, and they mainly skirt the coastlines of islands, large and small. Cuba’s reefs, namely the southeastern Jardines de la Reina, or Gardens of the Queen are some of the most pristine due to their long standing protection enacted by Fidel Castro, who was an avid diver throughout his dictatorship.

Like all coral reefs, Caribbean reefs buffer local economies by supporting dive and snorkel tourism, sport fishing, and artisanal (or small-scale) fisheries. As larger, open ocean fish become commercially extinct, coastal fisheries are increasingly targeting small, colorful reef fish using indiscriminate methods like fish traps to scoop up whatever is available. Because coral reefs rely on their fish residents to survive and visa-versa, this is an extremely worrying trend.

Reef Building Corals

Reef-building/stony corals come in diverse shapes, including cups, plates, bowls, boulders, and pillars. Each one is a home for diverse creatures like worms, fish, mollusks, and crustaceans. Corals themselves are sometimes referred to as holobionts, or whole beings, because they are made up of both algae and coral tissue acting in concert. Each coral species, and even individual coral genotypes, host their own preferred algal type, or clade. In return for having a home in the coral tissue, the algae supplies the coral animal with a significant amount (up to 95%) of the energy it acquires through photosynthesis. These symbiotic algae, known to science as symbiodinium or zooxanthellae (zoox for short), is thus essential to a coral’s capacity for long term survival. This becomes especially significant when higher than usual temperatures and subsequent heat stress causes corals to expel their friendly zooxanthellae, leaving behind a colorless, and soon to be starving animal. Bleached corals must be sustained solely by planktonic food that can be caught by the coral’s tiny stinging polyps, and though bleached corals can recover their algal friends, they will be much more susceptible to further stressors until they do so, and are thus more likely to die unless conditions improve.

When corals die, macro (large) algae overtake the dead skeletons and create what scientists call an alternate stable state. In other words, the capacity for corals to recover and re-populate a macro algae-covered reef becomes much less once the algae have taken over all the available habitat. Faced with consecutive, record-breaking temperatures every year – the result of anthropogenic global warming – in addition to a wide range of burgeoning human impacts like the physical destruction of corals, poor water quality, and the loss of keystone species such as parrot fish, grouper, and sharks, we are every year seeing new areas where coral reefs are bleaching. When the corals expel their symbiotic algal guests they lose a critical energy resource and easily succumb to further impacts, like a nutrient boom from run-off or a tropical storm. Indeed, we are on a speedy path to losing all the world’s coral reefs within decades if we do not act now.

What is more, given the importance of coral reefs to human wellbeing, our species might just as well follow them out the door. To prevent coral reefs from slipping through our fingers, scientists are trying desperately to understand what makes certain coral species, and genotypes within species, more resilient to higher temperatures, prevalent diseases, and other critical impacts. Once identified, we hope that these heartiest of corals can be manually propagated by applying the growing body of knowledge provided by coral research and restoration practitioners. What is more, we must adopt large-scale, integrated, and ecosystem-wide marine protection regimes that realistically minimize the entire range of human impacts on remaining coral reefs. Fortunately, we yet have the capacity to fully protect what little is left of these precious coastal and marine habitats.

Coral Restoration Field Work 

Everything slows down after a rainstorm, and just moments ago I found myself being observed by the world’s second smallest hummingbird just before locking eyes with a leaf-green anole lizard – a common visitor that usually scatters when I walk up the green cement stairs to my lodging at the Puntacana Ecological Foundation (PEF). The nonprofit body of the owners of much of Puntacana is housed in a hurricane-proof building, neatly shaded by thatched palm awnings, and painted in the red and blue of the Dominican flag, plus a healthy dose of industrial green. Just outside the building are plant nurseries, botanical gardens, and a nature reserve with crystal clear, freshwater lagoons that percolate from the porous, calcium-carbonate ground. There is even a large pen for the endangered rhinoceros-iguana (Cyclura cornuta), tarantula covered rainforest trails, towers for juvenile, endangered Ridgway’s Hawks (Buteo ridgwayi) to roost and feed. These are plagued by an introduce parasite that eats them alive as chicks, so helping them felt extra rewarding. Importantly, there is an apiary with honeybee hives, where much like people, bees bustle around in colonies, overheated and driven by their own instinctual exertions. Not far is the azure coastline with its gorgeous white sand beaches frequented by celebrities and people from as far as Russia and Japan.

I had arrived in Puntacana with the title of Coral Reef Restoration Intern and Scientific Diver. On my first day my team and I set out to monitor water quality from a large dive boat from the crowded tourist haven of Bavaro – a Cancun of the northern Caribbean with run-away development, poor waste management, and rapidly eroding beaches. Indeed, my first impression was an all too familiar site – plastic trash haunting the shoreline. To the amusement of a few locals, I made a point to collect some of it and deposit it in a nearby trash can as a small favor to the local pelicans. Three hundred meters off the reef crest the boat captain spotted a family of humpback whales blowing grey water vapor into the air. I longed to swim with them and for the warm embrace of the Caribbean Sea. The summer before, I had sailed and dived the nearby Leeward Islands with international high school students from Broadreach Summer Camp, exploring the fragile and rapidly disappearing coral reefs that I would now be studying and helping to restore. Already, the Caribbean has lost around 90% of its reef building corals and the future is not so bright for the ecosystem they have created over millions of years.

Coral restoration is a theoretically simple, but a practically and physically intensive process that involves growing coral fragments in an aquaculture lab or underwater coral nursery in the open sea. After growing the corals under the best possible conditions, they are then “out-planted” onto a denuded reef, usually atop dead coral skeletons. The hope is that they will then continue to grow on their own, and eventually reproduce to create new, wild colonies. But coral restoration is just one tool and given the scale of mass mortality events the practice has little hope of saving reefs on its own. So, at the same time as we work to restore corals, we must also be mitigating the many human impacts that weaken corals’ capacity to grow, reproduce, and resist being overgrown by various species of algae and/or overcome by disease.

A Presidential Act specifically protects coral reefs in the Dominican Republic (No. 112/96), but this protection on paper is fruitless without the political will and financial support to maintain well-trained and non-corrupt park rangers who can effectively enforce the law. What is more, the DR’s population has risen drastically, from two million in the 1960’s to over ten million people today. Rivers and coastlines have thus been steadily degraded, and soil erosion and sedimentation from sugar cane and other agricultural practices have suffocated the nearshore reefs.

The burgeoning population also contributes ever more untreated wastewater and other pollution to the reef environment, while constantly removing more and more living organisms for commercial exploitation. Commercially harvested species in the Eastern DR include the Queen Conch, Strombus gigas, the Caribbean Spiny Lobster, Panulirus argus, fish of the Grouper family, Serranidae, Snapper family, Lutjanidae, and increasingly, Parrotfish family, Scaridae. Black corals, hermit crabs, various ornamental reef fishes, sea stars, sea urchins, and “live-rocks” for the souvenir industry are also taken with regularity. This broad harvest across the food web makes it difficult for the coral reef ecosystem to recover from major mortality events  – such as one in 1983 that signaled the arrival of a warmer planet combined with an El Niño weather event. Warm seas led to a disease that killed off the grazing, Caribbean long-spine sea urchin (Diadema antillarium) which plays a key role in grazing reef algae and thus allowing for coral growth and feeding. Indeed, as more and more species are removed, denuded reefs become ever more prone to being overtaken by slimy algae that is of little benefit to humans or to the wider ecological community.

As coral restoration practitioners, we literally and metaphorically hold tightly to the last remaining fingers or spurs of reef that are still covered with gorgonians (sea fans), other soft bodied corals, and healthy, yellow sea trees of elkhorn coral, (Acropora palmata). Coral restoration work is useful for scientific experimentation and has become a popular way to increase awareness about the plight of corals. But more importantly, growing and planting corals, in the tradition of Mendel’s pea plants, is the best way to ensure the continuing genetic diversity of unique coral phenotypes. Within this diversity we would hope that some colonies will be better at resisting ocean warming and bleaching – a phenomenon that has been up to ten times more prevalent globally over the past five years! The good news is that NGOs, diving centers, private sector institutions, local communities, and government authorities in the Eastern Dominican Republic, namely in the township of Bayahibe, have a long history of working together to help preserve and restore coral reefs. This work is done through: (1) the use of Marine Protected Areas and Coastal-Marine Spatial Planning regimes, including no-take and restricted fishing areas, (2) coastal waste-water management, (3) removal of invasive lionfish (Pterois spp.), and (4) coral restoration. A 2021 study revealed that the DR’s eastern reefs are in “fair” condition, despite the lack of coral cover, and more resilient to pressures such as increasing tourism and the rapid spread of coral disease than other more vulnerable Caribbean reefs.

From 2011-2016, the biomass of both herbivorous fish like parrotfish and commercial fish like snapper and grouper increased consistently, and an average of 422 lionfish were removed by community groups each year. Coral restoration meanwhile showed considerable promise, with an 80% survival rate of corals at the primary nursery (known as The Aquarium), and 70% at outplant sites (where nursery coral fragments are taken and literally planted on the dead reef). If properly cared for, these reefs may serve as THE example for the wider Caribbean on how best to conduct integrated, data-driven restoration and management efforts to save coral reefs. Improved management will be achieved mainly through improving water quality by limiting polluted run-off and dumping, continuing long-term ecological monitoring, fostering more sustainable and low impact forms of tourism, improving fisheries policy and enforcing Marine Protected Areas (MPA’s), and physically linking MPA’s by applying the concept of seascape connectivity. These actions have been shown to buffer healthy reefs and local economies, and private programs like the Iberostar Group’s “Wave of Change,” in tandem with strong local commitment, environmental education, and robust law enforcement, do indeed have the capacity to change the ecological, economic, and social future of the Dominican Republic and wider Caribbean, provided we keep the pressure on.

Our work in the Dominican Republic focused on corals in the genus Acropora, a type of reef building coral that provides excellent habitat for a wide diversity of species, namely reef fish. These branching, colonial invertebrates resemble ungulate horns and are commonly called staghorn (Acropora cervicornis) and elkhorn (Acropora palmata) corals. Both species are listed as threatened by the U.S. Fish and Wildlife Service. Relative to other corals, species in the genus Acropora grow relatively quickly. They also thrive in shallow, nearshore, low-nutrient waters where much tourism and artisanal fishing activities take place. The hope that we can quickly foster Acropora species’ capacity to form complex natural habitats is what makes them a restoration priority. 

Acropora branches are cream and purple in color the coral tissue is itself purple and the cream color pertains to the symbiotic algae that lives within the tissue; the tops of stag horn coral branches, having less surface area, also have less algae and are thus more purple than the stalks and bases. The stony, or reef-building part of the coral is its extensive skeleton made primarily of calcium carbonate recycled from various species of calcifying algae which also grow on the reef. The skeleton is a porous housing comprised of myriad little cups, or corallites, each containing two-millimeter-wide colonial animals called polyps. Coral polyps are all interconnected by a nerve net, such that they can retreat all together when just one is accosted. Like stinging jellies, corals are in the phylum Cnidaria. Coral polyps have six, or multiples of six, tentacles that they extend further out at night when they do most of their feeding. During the day, the coral harvests the sun’s energy through photosynthesis conducted by the symbiotic algae living in its tissues. In return for having a home in the coral’s tissues, the algae share a percentage of the sugar it produces. At the pointy end of each staghorn coral branch is an apex-polyp housed in an apical, a calcium cup that extends a bit farther out than the rest like a little plug. This is the part that does the growing, cloning itself and producing buds at its base. The apical even steers the coral branch towards the sunlight, much like a plant will bend to maximize light absorption.

To become coral restoration experts, my fellow interns and I had to first learn the ropes – quite literally. Mid-water nurseries are underwater rope ladders with weights on the bottom and floats on the top, and just one of several structures built to grow corals from small fragments to larger ones able to be out planted across the reef. In a typical mid-water nursery, the arms of each ladder are about five arms-lengths wide, and between them are five rope rungs. Each rung is “planted” along its length with small coral fragments (frags) tied to the rope a hand’s length apart. We also learned to build benthic (sea bottom) structures called A-frames – four foot long, meshed rebar half pipes, open side down, coated with resin to deter algae. Other nursery structures included flat, rectangular rebar tables and trees made of PVC piping branches on which frags hang down from fishing lines like little Christmas ornaments. Each type of nursery or coral frame has its advantages and disadvantages, and details such as their placement underwater are critical to the success of the coral fragments they host.

Before sinking the frames we paint them in a strong resin as coral frames – namely the tabletops that host the elkhorn / palmata coral fragments, tend to collect sediments, grow hydroids (stinging, feather-like animals), and get overrun by filamentous algae that blocks the corals’ capacity for food and light intake. We must constantly brush them clean. This is done to the satisfaction and amusement of the many herbivorous fish that live among the coral, such as wrasses, tile fish, file fish, and slippery dicks. Darting around us and pecking at the free food, they mutualistically offer companionship and their beautiful colors in return. The pink one even lets me pet her know and again, or is it he? It’s hard to know when they keep changing sexes.

But not all the life in the nursery is friendly, and I don’t mean the six-foot barracudas that have claimed the territory as their own. Carnivorous fire-worms in the genus – Annelida and more innocuous looking snails, redundantly named short abbreviate coral shells, or Coralliophila abbreviata are the corals’ mortal enemies. Victor Galvan, the Mexican American biologist who took this project on over a decade ago, held up one of the tiny, algae covered culprits on my first day, explaining how they consume coral tissue at a greater rate than any other prey species and leave bare coral skeletons in their wake. We were taught to deal with them without mercy and adopted a trapping technique to destroy fire worms as well. This is, after all, a deliberate intervention, and to balance the effects of anthropogenic pressures, we must also contend with natural ones.

Areas with multiple frames are known as coral nurseries and our primary nursery in Puntacana is known as “The Aquarium.” A sandy haven tucked between the reef crest and fore-reef, The Aquarium nursery is complete with tagged and numbered rope ladders, A-frames, and tables, all planted with abundant fragments of living staghorn, elkhorn, and finger corals (Porites spp.). The nursery has been accepted as a “total-no-take area” by local fisherman and is visited only by respectful divers and snorkelers who give it the look of an undersea aquaculture site from Jules Verne’s “Two Thousand Leagues Under the Sea.” Even the broader setting – Hispañola, the infamous hub of the 18th century slave-trade echoes the life of Captain Nemo and his aquanauts – who were former slaves turned ocean stewards. Only Nemo and his crew, at least in the movie, were not Taino Islanders or Africans taken to the Americas. Perhaps Verne intended them to be but could not take such a bold statement in his day so he made Nemo an Indian Aristocrat come to seek his revenge on the British Empire. But I digress.

In total, The Aquarium houses around 30 frames under which fish of all shapes and sizes take refuge and/or seek their prey. Hammerhead harks, manatees, and eagle rays were also spotted during my stay. But more importantly, a thriving nursery means having a consistent source of live coral branches that, after about a year of continuous growth, can be broken off and transferred, piece by piece, to the denuded reef by re-attaching them to dead coral skeletons using a hammer, nails, and plastic zip-ties. Other restoration practitioners use cement in tubes to glue coral frags to the reef. As I am about to describe in this article, being an aquanaut ‘aint easy, and we set an ambitious goal of restoring 800 square meters of stag horn coral across multiple outplanting sites, and collecting 100 square meters of new elk horn coral fragments to grow in our nursery. All of this was to be accomplished by three interns in less than three months (May-July).

By restoring coral colonies in places where conditions are optimal, we hoped to give the eastern DR’s last Acropora colonies a fighting chance. In Puntacana, there are over 13 coral nurseries, making it the largest restoration effort in the Caribbean, or close to it. Some nurseries are used to maximize coral production while others are set up to raise awareness and largely managed by dive shops and other local tourism providers working under our institution’s permits and supervision. Even PADI joined forces by offering a Coral First Aid Specialty Course which I would highly recommend to all divers and coral reef lovers who want to learn the nuances of coral growth while developing critical dive skills like buoyancy.

Because of its scarcity stag horn coral (Acropora cervicornis) is rarely collected from the wild and is instead pruned from “stock” growing in the nursery. The amount of stag horn coral that we out-plant onto the reef is gauged first when we prune the coral fragments and measure their Total Linear Extension (TLE) – the sum of the length of each broken fragment, adding up the length of its trunk and all its branches. When it came to elk horn coral (Acropora palmata) on the other hand, our task was to seek “fragments of opportunity,” as Victor calls them, or wild pieces of A. palmata that have broken off in storms and are now lying about the reef.

Searching in areas that are at least 40m apart from prior sampling sites promotes finding genetically unique frags, and we would free-dive from five to twenty-five feet to discover and collect these broken pieces of magical, golden elk horn, which would then be transferred to the Aquarium Nursery. Here, sitting and sip-tied atop cured cement “cookies” on rebar tables, we hoped they would have a better chance of growing into larger corals with greater survival rates than had the fragments been left lying in the reef crest. 

Collecting fragments of elk horn coral went something like this: Papujo, our boat captain and a local fisherman, would apply his intimate knowledge of the reef to locate areas where we might find fragments – without his knowledge of the reef we would have bumbled about like lost children in a crowd. Once fragments were located via an initial snorkel survey, a free diver would swim down to it, and on the first breath-hold break down the larger fragments into smaller pieces by chipping at their sides with a large hammer. The fragment could not simply be smashed in the middle, because this would likely destroy the skeletal structure. Smaller frags grow even faster and by splitting one large piece into many we could exponentially increase the surface area of tissue that would grow in our nursery. Again, if we were to simply scatter these newly broken fragments across the wild reef, most of them would die, and thus allowing them to grow in our nursery and then attaching them firmly to the reef meant increasing their chance of survival.

On the second breath, we would collect the newly broken pieces and bring them to the surface. With a hand wave, Papujo would then bring over the boat, which could not linger safely in the surf-zone, and another person on-board would take the fragments from the free diver and place them gently in multi-colored buckets of seawater. Because each fragment of opportunity represents a potentially new genotype that we are transferring to the nursery, a GPS coordinate was taken right away to mark the specific spot where the frag was located. The GPS coordinate is then matched to the specific color of zip tie that would be used to secure it to a frame in the nursery, for example using the code: 651_purple_red. Using this method, we were able to keep track of potentially new genotypes in the nursery and the location on the reef where they were discovered. After all the frags are collected and placed in buckets, it becomes a race to get them back underwater in the nursery, and board the small motorboat, one can feel and smell the spectacularly thick mucus-covering that protects the highly sensitive elk horn corals from the sun, salt, and sediments. Upon reaching the nursery, the buckets of frags are handed down to a diver who will proceed to zip tie them onto cookies – hardened cement pancakes with holes in them. Once the corals are secured, these cookies are then themselves zip tied to the tabletop frames. The work involves expert boatmanship, high-rates of air consumption when diving, and dangerous close-calls, like when the metal bar of a frame tore through the leg of my colleague’s wetsuit. Despite our most intense suffering, however, the little fish are always amused and enthused by our exertions.

The most difficult part of the restoration process is out-planting: carrying coral fragments harvested from out of the nursery and attaching them onto the reef face. Successful out-planting requires a fair amount of strategy and long-term knowledge of the reef. For example, we might add more coral to previously restored areas that are showing promise or attempt to create and test newly refurbished colonies. The process begins with breaking coral fragments from off the nursery frames, measuring them one by one, and lifting them out of the water and onto the boat in crates so that we can transport them up to several miles to various out-planting sites. This too involves a great degree of expediency so that the corals don’t die from exposure – our Caribbean Acropora corals do not like to be out of the water for even brief intervals, unlike other Acropora genotypes like the ones I saw when visiting the Great Barrier Reef Marine Park that are accustomed to being exposed for hours when the tide recedes.  

In Puntacana, we outplanted at around 40 unique sites. While some were new, most sites were ongoing study areas. Outplant sites are “discovered,” by having a snorkeler drag on a rope behind a moving boat as he/she looks for areas with certain biological and physical features that indicate generative, reef habitat. Indeed, one of those towable sub-wings would have been good to have. Suitable locations are then marked by GPS and by dropping temporary buoys, and I cannot emphasize enough the importance of having well-labeled and clearly organized GPS points. It was also advisable to use discrete sub-surface buoys that will not be removed by locals, as buoy theft is a common problem. The expensive rebar used to build nursery structures is also sometimes stolen, pointing again to the critical importance of community buy-in and support. Teamwork, including involvement from fishermen, dive shop guides and managers, scientists, and restoration colleagues was critical to our coral restoration effort. 

After locating the out-planting site, often a time-consuming task, we enter the water with full tanks of compressed air, around one hundred stainless steel nails – our most costly resource, neon flagging tape, abundant zip ties, and stainless-steel mallets. First, we put down as many well-spaced nails as possible into the substrate, not so softly that they will fall out, nor so hard that they will bend, and we mark each one by tying a bit of the neon flagging tape to it. These re-location spots must be at least one meter apart to allow for growth, and high enough above the sand to prevent sedimentation – a common cause of coral mortality. This initial process takes a full tank or two of air, and we normally wait until the following day to harvest and attach the coral frags to the flagged nails. Tasks like attaching flagging tape to the nail before the swiftly moving surge drags you away, let alone attaching the porcelain-like corals without snapping them have to be gradually mastered. Objects also like to disappear underwater, and we eventually discovered that heavy duty fanny packs are an essential item for carrying nails. There is always room for creative methodologies, and I devised a better collection method for collecting the ends of used zip-ties which we clip to reduce areas where harmful algal can grow. This consisted of attaching a capped, empty plastic water bottle, with an X cut into the cap, to my BCD shoulder strap and stuffing the zip-tie ends into the cap. By the end of the day, the bottle was so full of colorful tie ends and flagging tape pieces that it looked like an art installation. It certainly disturbed me to put so much plastic onto the reef, but so far, this is the most viable method of out-planting. Conservation is, after all, defined by contradictions and compromises. The coral tissue will eventually engulf the plastic, but it will always be there like a prosthetic limb. On the other hand, there is a sure satisfaction that comes with leaving a previously denuded site brimming with branching corals, and even the fish appear to be grateful for the change as they duck in and out of the newly placed branches.

As we out-plant, there is a lot to keep track of. We count how many nails were placed in each site when setting up for the out-plant, how many coral fragments we attach, and one of us measures each segment of every fragment, adding them together to get the Total Linear Extension (TLE), of coral tissue that has been planted. By keeping track of the TLE, and incorporating estimates of coral mortality, we can have a rough idea of how much coral tissue has actually been restored to the reef. Stag horn coral tissue growth is also estimated by photographing the restored fragments at out-planting sites at three different time intervals and then analyzing the amount of coral cover using a software program called Coral Point Count (CPCe). For the elk horn coral we used another program called Image-J, in which close-up photographs of our growing fragments are traced by hand and analyzed by area using a corresponding scale and pixel size.

As we face ever more severe tropical storms and rising sea levels, the new coral colonies will both provide habitat and protect the coastline from wave energy – a much cheaper solution than spending millions of dollars on ever-crumbling beach walls. Unfortunately, local out-planted colonies only seem to survive for around 2-3 years, but this is hopefully sufficient time for them to reproduce naturally, spreading their unique genotypes along the restored reef. Indeed, to really understand the purpose of coral restoration, we must first understand coral reproduction.

Stony corals can reproduce asexually, by cloning themselves, or as is most common in Acropora corals, when branches fragment, or break-off with storms and grow into new colonies wherever the current lands them. Corals are also hermaphrodites in that they produce both male and female gametes, or sex cells, and can thus reproduce sexually as well. Sexual reproduction happens when the colony’s polyps – the tiny mouth-like feeding and breeding structures, release, through their single opening, both sperm and egg cells into the water column. In every region where corals exist, there are annual, large-scale, synchronized spawning events, usually occurring between August and October, at night, and on a full moon – the gravity of which literally pulls the sex cells out of the polyps.

Once in the water, female and male sex cells collide, are fertilized, and become spats – coral larvae that drift until they can find a suitable surface to settle and grow. Elk horn coral (Acropora palmata) larvae prefer shallow, high-energy environments where both light and food are abundant. Sexual reproduction is crucial because it allows for gene flow – the exchange of genetic material among unique coral colonies. Gene flow means increased potential for both helpful and harmful genetic mutations, which can mean the difference between life and death in times of great, man-made ecological changes like the modern day. The most important mutations will be ones that aid in resistance to coral diseases and those that increase tolerance to the oceans warming temperatures and increased acidity – conditions resulting from anthropogenic, or man-made, climate change.

Coral spawning events are indeed a spectacular demonstration of the timeliness of nature. In fact, researchers can know almost the precise date that spawning events occur for specific species by applying a probability curve based on previous records for an area. By spawning at different times, different coral species can minimize hybridization – the mixing of species, which can lead to infertility. When elk horn (Acropora palmata) and stag horn coral (Acropora cervicornis) cross-fertilize, for example, they produce a hybrid known as Acropora prolifera. Interestingly, this hybrid will have a different phenotype (physical characteristics), depending on which species the egg originated from. What came first, the coral or the egg?

On August 22nd, 2016, at around 8:30pm, four days after an incredible full moon, several of the stag horn coral colonies growing on metal frames 15 feet deep in the protected Aquarium nursery began to spawn. Victor Galvan, the project Director, starting whooping as the polyps retracted and let loose their gametes into the water column, which drifted back and forth like tiny stars in a wishy-washy universe. 

Back in the lab, close to midnight, Dr. Galvan placed some of the eggs that we collected using a large mesh funnel suspended over the coral colonies under a microscope. I was skeptical that we could capture something so infinitesimal as sex cells in action, but sure enough one could see sperm cells darting around the eggs like gnats, attempting to penetrate the clearly visible cell walls. We could even see spicule-like extensions protruding from the eggs, as the cell wall seemed to deteriorate before our eyes – the first stages of fertilization were taking place! It filled us with a sense of wonder and accomplishment to witness the complete cycle of coral restoration, from split to spat. Because we were tracking around fifteen different genotypes in the nursery, we could be almost sure that unique genetic material was effectively being exchanged, making us just little bit more hopeful for the future of these colonies. 

 

 

(Juvenile) blue head wrasses take refuge among a restored colony of stag horn coral

 

Jose, better known as Papujo, enjoys diving in The Aquarium nursery.

 

 

 

Independent Research Projects

We were fortunate, during our internship, to each take on an independent research project related to our coral restoration work, which gave us tools and inspired us with ideas that we might apply in the future. My colleague Nicole Sikowitz took on a coral-bleaching project that involved monitoring stag horn coral fragments of different genotypes (genetic make-up), under two different light and temperature regimes by placing them on floating frames at different depths. She learned that wider temperature and light ranges need to be used to see clear differences in degrees of bleaching and that the Australian Coral Watch Color ID Card (for monitoring bleaching) was not ideal for use in the Caribbean. This led to our making of a new color guide by using pictures of local corals and the Adobe Photoshop eye-dropper tool. We also learned that little squids like to aggregate under floating, horizontal mesh frames placed ~1.5m below the surface.

My colleague James Fifer ushered in a new era in coral restoration by experimenting, for the first time locally, with restoring brain coral (Pseudodiploria spp.) using a technique pioneered at Mote Marine Lab in Florida called “micro-fragmentation.” This involved cutting fragments of <1 cm with a diamond-band saw, then fixing these tiny frags to tiles inside a laboratory tank. When big enough to survive in the ocean, these will be out-planted and allowed to “re-skin” the dead, calcium carbonate skeleton of a massive coral (vs. a branching coral) with live tissue. When his brain corals were struggling to survive in a small tank, with excessive variation in UV light and an unsteady temperature (the security guard would constantly unplug or move his fan), James spearheaded an effort to improve our success with growing elk horn fragments in the nursery. James also explored the potential of restoring finger coral (Porites spp.), a coral type that was much more abundant just six years ago (personal communication with Victor Galvan) and that can be more easily cemented to the reef.

My own project furthered the principles of the “ecosystem approach,” by looking at a species that could be key to maintaining the conditions needed for a healthy coral reef to persist – the sea cucumber. A cousin of the sea star and sea urchin in the phylum Echinodermata and class Holothuroidea, sea cucumbers have been hugely over fished, often illegally and without regulation, for a black market in Taiwan and Hong Kong, where they are both a fancy food and used in traditional medicine. As benthic (bottom-dwelling), filter-feeding invertebrates, sea cucumbers play an important role in recycling the few available nutrients in a coral reef’s low-nutrient environment. The Foundation might even commence an aquaculture project and/or other management initiative for sea cucumbers like Holothuria mexicana  in the near future.

 

Sources:

Conservation Actions and Ecological Context: Optimizing Coral Reef Local Management in the Dominican Republic: Cortés-Useche et al. (2021).