Florida Aquarium in Tampa advances coral spawning research

Working laboriously over tanks of filtered seawater, and with tiny vials of coral spermatozoa frozen in liquid nitrogen, researchers at the Florida Aquarium in Tampa have taken a second major step toward producing living corals to replace those being killed by disease and climate change in Florida’s barrier reef.

The researchers, based at the Aquarium’s Apollo Beach campus in south Hillsborough County, have successfully bred wild corals with those growing in their own “coral farm,” using frozen sperm from wild corals. 

The goal: To produce hybrids genetically diverse enough to survive changing sea conditions and diseases including one called “stony coral tissue loss,” which has driven once-common species to the brink of extinction in Florida.

“We’ve lost as much as 90 percent of the individuals of some species in Florida, to the point that their ability to recover naturally is limited or impossible,” says Marine Biologist Keri O’Neil, who leads the effort at the Aquarium.

The result of her team’s latest work is thousands of tiny, reddish-brown coral colonies growing on tiles in tanks at the Aquarium’s Center for Conservation in Apollo Beach. 

While Aquarium visitors see plenty of colorful and strange marine creatures, a side of the facility they don’t often see is its focus on marine conservation work.

Most of it is carried out at the Center, a collection of greenhouse-like buildings housing labs, tanks, pumps, and filters on land provided by TECO (Tampa Electric).

The research work focuses on sea turtles, sharks and rays as well as coral.

The Aquarium’s biggest conservation effort

The conservation work averages 7-10 percent of the Aquarium’s annual operating budget of about $30 million, and about 14 of its total staff of 245.

Workers rehabilitate sick or injured turtles for reintroduction to the wild. The shark and ray research focuses on reproduction, chiefly with bamboo sharks, southern stingrays and sand tiger sharks, a species once common but now increasingly rare.

But the coral research is the Aquarium’s biggest conservation effort. It’s an attempt to rescue an entire ecosystem, the Florida barrier reef, that supports thousands of species of sea life. It’s an effort comparable to the Everglades rescue, but far less well-known and with only a tiny fraction of the funding.

Most Floridians don’t realize the state’s barrier reef, extending the length of the Keys in the Atlantic, is a planetary landmark like the Everglades. It’s the third-largest barrier reef in the world after those in Australia and the Philippines, and the only one in North America.

The cause of the stony coral tissue loss disease is unknown. 

First noticed off Florida in 2014, it has now spread through the Caribbean. It kills primarily reef-building corals, including pillar corals, star corals and boulder-like corals that divers call “brain corals” because of the wavy ridge patterns on their surfaces.

But the disease is only the newest of several threats to the reef’s existence. Climate change threatens reefs throughout the world.

Corals look underwater like colorful rocks, small trees or flowers, but they’re actually colonies of tiny individual animals called polyps, whose shells, welded together into rock- or plant-like formations, make up the reef. 

Corals are highly sensitive to water temperature and chemistry, and because they live symbiotically with single-celled plants that need light, they require clear, unpolluted water.

Warmer ocean water contains more dissolved carbon dioxide and therefore is more acidic. That situation can prevent the corals from forming their calcium carbonate shells, or even dissolve the shells.

Algae, which thrives in polluted water, can overgrow hard surfaces, preventing new coral polyps from implanting themselves and starting colonies.

Coral juveniles will continue to grow if returned to the wild

Corals reproduce by releasing sperm and eggs into the water in clouds, an action triggered by seasonal cues from sunlight, moonlight and water temperature. The eggs and sperm combine to produce larvae which float freely in the water until they land on a surface for implantation.

About two years ago, O’Neil and her staff took their first major step in duplicating that process on land. They used controlled lighting and temperature to induce corals rescued from the wild to spawn in the tanks at the Center for Conservation. They were able to produce larvae that implanted on tiny squares of ceramic tile and started to grow. 

Those coral juveniles will continue to grow if returned to the wild, a process that’s been successfully carried out in Florida and elsewhere. But because the juveniles are all genetically identical, they would all be vulnerable to the same diseases and environmental stresses. A single disease or pollution event could wipe them out.

To achieve a genetically diverse population for replanting, the researchers needed to interbreed with wild coral. This is the step O’Neil’s team, working in conjunction with researchers at the University of Miami, have now taken.

They used ova from “mothers” growing in the Aquarium -- brain corals taken from the wild before the advent of the tissue loss disease -- combined with sperm collected in the sea from wild corals and shipped here frozen in tanks of liquid nitrogen.

The University of Miami, meanwhile, reversed the process, using sperm from corals growing at the Aquarium combined with wild-collected ova. 

Aquarium workers drove the frozen sperm in cryogenic tanks of liquid nitrogen from the Aquarium to Miami and returned with tanks of wild-collected sperm.

Freezing the sperm to keep it alive and then thawing it to produce viable larvae were the new steps.

“The next major step will be to figure out which parents are the best,” O’Neil says -- which corals produce juveniles most resistant to temperature changes, acidity, and disease. That will include exposing some to the tissue loss disease to find the survivors.

The most laborious part of the work

Meanwhile, the juvenile corals are growing in their tanks, tiny dots an eighth-inch or less across.

Workers must clean off the algae that grows on the tiles and in the tanks, which could smother the coral babies. It’s the most laborious part of the work, but they get help from thousands of half-inch long marine snails that crawl around the tanks eating the algae.

“We spend enough on snails to pay another staff member, but the snails work 24/7 and they don’t get benefits,” O’Neil notes.

In nearby tanks, some 5,000 coral colonies about a year old have reached half an inch to an inch in size. When they reach 1 to 1½ inches, they’ll be ready for replanting in the ocean.

And in another project, researchers are breeding long-spined sea urchins, a once-common species on the Florida reef that’s a voracious algae-eater. Its numbers declined sharply due to disease in the 1980s, leaving more of the reef covered with thick coatings of algae that smothers coral.

O’Neil acknowledges that the Aquarium’s work is a small first step toward rehabilitating the massive damage done to Florida’s reef by pollution, climate change and disease, but at least it’s a start.

“We’re expanding rapidly,” she says. “By this time next year, we hope to have twice as much capacity and staff.

Duplicating awe at the sight of coral reefs

In an interview in 2019, just after her team completed the first step of getting corals to spawn in captivity, O’Neil described how she became interested in marine biology and specifically coral reefs.

It happened when she went snorkeling off Fort Lauderdale in the 1980s, when Florida reefs were much healthier and crowded with sea life.

“There was a little bit of fear, being a kid,” she said. “I was like, what if there was a shark? 

“But that was quickly overcome by the wonder of everything I was seeing. … The coral reef is just this overwhelming diversity of life. I wanted to know what everything was and what its purpose was and how it all fits together. 

“I now find myself studying the decline of that ecosystem and that can be disheartening. Part of what keeps me going is wanting more children to be able to wonder at the beauty of this coral reef like I did.”

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Read more articles by William March.