Spawning an Intervention

An international team of scientists is mastering the art and science of raising coral babies

Valérie Chamberland flicks away an agitated crowd of silvery butterflyfish, then descends slightly for a closer look at the mound of brain coral. She inspects the meandering grooves on its surface, looking for the tiny white bumps that appear immediately before its annual spawning. For the butterflyfish, the pinhead-sized bundles of sperm and eggs released during a spawning event are a calorie-rich feast; for Chamberland, they’re the raw materials she needs to further a long-running mission.

photo of coral reef
Chamberland and her colleagues have learned to fertilize coral eggs in a lab and foster young corals until they are ready to grow on a living reef. After years of research, the field of assisted recruitment is about to venture into new territory.

Over the past two decades, Chamberland and other scientists throughout the Caribbean — many of them now associated with a research and conservation group called SECORE, which stands for Sexual Coral Reproduction — have stubbornly advanced the art and science of raising coral babies. Through trial and error, these researchers have learned to better predict the quiet, hidden phenomenon of coral spawning, to fertilize coral eggs in the lab, and to foster young corals until they’re ready to grow in the open sea, on a living reef.

Newborn corals are, in their way, as high-maintenance and idiosyncratic as their human counterparts, and the process of raising and releasing them, formally known as “assisted recruitment,” is full of frustrations and disappointments. Thanks to some recent successes and to rising interest from conservationists, however, the job is becoming easier and cheaper. The progress is such that on Curaçao this past June, Chamberland and her colleagues hosted an intensive workshop in assisted recruitment for 10 park rangers, conservationists, biologists, and others from a half-dozen Caribbean islands, intending to both share the techniques they’ve developed and, in time, learn from the experiences of new practitioners.

Chamberland, who moved to Curaçao from Québec nearly a decade ago, sometimes feels as if she’s counting down to a rocket launch: After years of careful preparation, assisted recruitment is nearly ready to blast off into new territory.

On the reef, Chamberland finishes her inspection of the brain coral and leaves the butterflyfish to their vigil. She surfaces and takes off her mask, freeing its rubber strap from her dark hair. The setting sun pinkens her often serious face, and she grins. “Tomorrow night,” she says, her consonants softened by her native French. “It’ll happen tomorrow night.”

On the first morning of the Curaçao workshop, Mark Vermeij wants to make two things clear: Raising coral from larvae isn’t easy, and baby corals are not, on their own, going to save the world’s coral reefs. “People have approached us and said, ‘Ah, that’s nice, because now the Great Barrier Reef is fine,’” he tells the participants. “And it’s like, ‘What on earth are you f—ing talking about?’”

Vermeij is a professor at the University of Amsterdam and the research director of CARMABI, a longstanding marine research and conservation center on Curaçao and a key supporter of SECORE. Originally from the Netherlands, he has studied coral spawning here and elsewhere in the Caribbean since the early 1990s. His imposing bulk, gray curls, and often-furrowed brow give him a piratical air, and his blunt opinions, delivered in fluent English, are punctuated with the occasional Dutch exclamation.

In a narrow, air-conditioned classroom at CARMABI headquarters, below a faded photograph of the Dutch king and queen, Vermeij reminds the participants that restoring coral reefs isn’t just about putting more coral in the ocean. It’s about dealing with chronic local problems like coastal development and water pollution — not to mention the multilayered, and increasingly obvious, effects of climate change on ocean habitats worldwide. “This is not a wonder tool,” he says sternly, glaring at the participants. “It will greatly depend on everything else you are doing, and everything else you are doing will depend on where you’re from.”

Despite his gruff manner, it’s clear that Vermeij is as pleased as Chamberland to be hosting this workshop. As the participants introduce themselves and describe their own attempts at coral restoration, Vermeij listens closely, asking questions and offering brusque encouragement.

Most people in this group are new to assisted recruitment, but everyone is familiar with the extraordinary — and extraordinarily complicated — life cycle of coral. That makes them unusual among humans, and unusual in human history, too. Not until the 1980s, after all, did researchers confirm that most corals can reproduce in two distinct ways: sexually and asexually.

Coral polyps, the tiny, tentacled invertebrate animals that, along with their symbiotic algae, form the living part of a coral reef, can reproduce asexually by budding off, or dividing, to form genetically identical versions of themselves. (What most of us think of as one coral — a ball, a column, a branching bouquet — is not a single organism but a colony of cloned polyps, nestled into a calcium carbonate skeleton formed over time by secretions from multiple generations of polyps.) Finger-sized bits of coral colonies can grow quite quickly via asexual reproduction, and conservationists around the Caribbean are beginning to “garden” these fragments: Francesca Virdis, the project coordinator of the Coral Restoration Foundation Bonaire, tells her fellow Curaçao workshop participants that her organization is encouraging the clonal growth of some 12,000 colonies of staghorn and elkhorn coral (Acropora cervicornis and Acropora palmata, respectively) by anchoring fragments on submerged scaffolds made of PVC pipe.

Once these cultivated colonies reach a certain size, they can be relocated and used to supplement the structure of reefs damaged by hurricanes, disease, or human activity. But Virdis and the other workshop participants know that coral gardening isn’t a wonder tool, either. To survive long-term, corals need not only structure but also genetic diversity, which is enhanced through sexual reproduction — the chance combination of sperm and eggs, or gametes, from different colonies. In most coral species, this cross-fertilization takes place during periodic spawning events, when colonies simultaneously release a brief blizzard of eggs and sperm into the open water. While colonies cultivated from fragments can eventually spawn and cross-fertilize, it takes years for any coral colony to reach maturity; the SECORE scientists believe that by cross-fertilizing coral at the beginning of the restoration process, they can bolster the variation corals need to evolve new defenses against changing conditions.

photo of coral reef
Rising ocean temperatures can cause colonies like these to lose the symbiotic algae that give them both their color and their primary source of food. If a bleaching even is severe and lasts for long enough, it can kill corals across an entire reef..

Many of the workshop participants live face to face with these changing conditions. Rita Sellares, the cheerfully determined executive director of FUNDEMAR, a small marine conservation nonprofit in the Dominican Republic, reports that several of her group’s coral gardens were smashed by recent hurricanes. Erik Houtepen, a young park ranger on the tiny island of Sint-Eustatius, says that his park’s gardens, which contained about 500 fragments, were completely destroyed in late 2017 by a double hit from hurricanes Irma and Maria; a few months later, after a laborious reconstruction, the gardens were again knocked flat, this time by a large storm surge. The park is experimenting with tying and gluing fragments directly to its reefs, and with scaffolds that can be sunk to deeper depths, further out of reach of storms. “If any one of you wants to be an intern for us, we could use you,” Houtepen says dryly.

Conservation of any sort is difficult work, and coral reef conservation can test the most optimistic soul: In the Caribbean alone, reefs are beset not only by destructive storms, but also by local pollution, rising ocean temperatures, at least 40 different infectious diseases, and the effects of worldwide ocean acidification. There is evidence that dust storms from the African Sahel region, exacerbated by climate change, carried a type of fungus into the Caribbean that now kills Gorgonian sea fans. Over the past 45 years, the overall extent of coral in the Caribbean has shrunk by more than half, both because colonies are dying off and, for reasons scientists don’t entirely understand, they’re not reproducing very well; in Florida, the extent of some coral species has declined by 90 percent.

While Pacific reefs have long been markedly healthier than those in the Caribbean, a series of enormous bleaching events, beginning in 2016, have affected massive swaths of the Great Barrier Reef and wiped out any remaining complacency among Pacific coral conservationists. (As seen in this earlier bioGraphic feature, Coral “bleaching” happens when ocean temperatures rise to levels that cause polyps to expel the symbiotic algae that give the hosts both their color and their main source of food.) Every experienced coral biologist, no matter where he or she works, has a story about a favorite reef that is forever changed.

Kara Rising, SECORE’s administrative manager, recently closed her psychotherapy practice in Ohio in order to devote herself to ocean conservation, and she’s often struck by the unrelenting emotional toll of conservation work. “There are times when I think, ‘Hey, should we have a bit of group therapy here?’” she says with a laugh.

Yet the grimmest story about the world’s coral reefs is also the simplest. For the conservationists in the Curaçao workshop, hope lies in complexity, in the many overlooked departures from the mean. Some corals are killed outright by bleaching, for instance, but not all; some species withstand it better, or recover from it more quickly, and some colonies within species seem to be more resilient, too. Some species, like the Caribbean’s threatened staghorn and elkhorn corals, grow very quickly but are particularly vulnerable to stress; other species, like the brain corals, grow slowly but can tolerate a lot.

“Corals are in a critical situation, but they’re not as flimsy as we think,” says Chamberland. “If we give them a chance to deal with just one or two stresses instead of six, some can survive, and those that do are the ones we should be studying. We should be asking, ‘What do they do that makes them win?’”

Chamberland, Vermeij, and the other researchers associated with SECORE have concluded that if they can help preserve variation, they can help preserve hope. And their first step toward preserving hope is to catch some corals in the act — to collect a few hundred thousand coral eggs and sperm as they’re released into the ocean.

photo of coral reef
Chamberland places a net over a colony of grooved brain coral that has just begun to spawn.

In the CARMABI classroom, Chamberland explains the protocol for gamete collection, laying out the cone-shaped nets that will be draped over the coral colonies and the plastic collection tubes that will catch gametes from Diploria labyrinthiformis, the species of brain coral affectionately known as D. lab. The nets are made from tarps, and none of the gear is high-tech—in fact, it’s deliberately designed to be low-tech, accessible to conservationists with even fewer resources than those at this modest field station.

Chamberland describes how gametes are handled back in the lab, long after dark, and how researchers sometimes keep watch on the embryos until the next morning. When she asks if there are any questions, Houtepen raises his hand. “So,” he says hesitantly, “do you sleep during this process?”

Chamberland laughs, but doesn’t answer. “Let’s do this,” she says.

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