In a tiny explosion of birth, coral scientists see hope for endangered reefs

Ridged cactus corals are native to Florida and the Caribbean, but a yearslong outbreak of a mysterious disease threatens their survival.
Image: Ridged cactus coral
Scientists successfully bred ridged cactus coral in a lab, offering hope for conservation researchers who are hoping to save Florida's endangered coral reefs.The Florida Aquarium

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By Denise Chow

Keri O'Neil almost missed the tiny grains expelled by the ridge cactus coral that she studies at the Florida Aquarium's Center for Conservation.

The small pellets, measuring just one-eighth of an inch long, were easy to miss against the colorful backdrop of knobby ridges and creases of the unusual species.

"That first day, we weren't even sure what we were looking at," said O'Neil, a senior coral scientist at the aquarium.

What O'Neil and her colleagues had witnessed was a ridged cactus coral giving birth.

The scientists say it's the first time this type of coral — which can look vaguely like a cross between a head of lettuce and a human brain — has reproduced naturally in a lab. The successful births offer hope for conservationists who are racing to save Florida's endangered coral reefs.

"The whole purpose of this project is to rescue corals and start a land-based breeding program for them so that we can restock the reefs in the future," O'Neil said.

Ridged cactus corals are native to Florida and the Caribbean, but a yearslong outbreak of a mysterious disease threatens their survival. The Florida Aquarium has partnered with the Florida Fish and Wildlife Conservation Commission and the National Oceanic and Atmospheric Administration's National Marine Fisheries Service to raise healthy corals in lab-based "greenhouses."

Ridged cactus corals are just one type being raised at the Florida Aquarium, but it's a species that scientists are eager to study. Known as brooding corals, these hermaphroditic specimens reproduce by releasing sperm into the water that then fertilize eggs inside the parent corals. And unlike many other coral species, which subsequently expel hundreds or thousands of eggs at a time in what's known as mass synchronized spawning events, brooding corals release a handful of fully developed baby corals, or larvae, over the course of weeks or even months.

"We've had anywhere from seven to 45 in a night, and they're still going," O'Neil said.

Since April 12, the scientists have counted 340 larvae, and although they start life by swimming around, the baby corals eventually settle and go through a metamorphosis — much like caterpillars as they turn into butterflies — to become so-called coral polyps.

The corals being raised at the Florida Aquarium were collected more than a year ago, but the goal is to eventually return specimens to their natural habitat.

Ridged cactus corals have been battered by stony coral tissue loss disease, which has left irregular white patches on specimens along the Florida Reef Tract, which stretches about 360 miles in an arc that hugs the southeastern Florida coast.

Researchers are unsure what causes the disease, but they are hoping that land-based breeding programs could help restore Florida's ravaged reefs.

The lab-based reproductive efforts could also benefit other threatened coral species around the world. Rising temperatures and warming oceans are threatening the Great Barrier Reef, which is undergoing its most widespread bleaching event. And a study released in February that was led by scientists at the University of Hawaii at Mānoa found that climate change could wipe out almost all coral reef habitats around the world by 2100.

But O'Neil said successful breeding programs are giving scientists hope that conservation efforts could save endangered corals around the world — even if they sometimes happen unexpectedly, as with the cactus corals.

"A lot of things with coral reproduction are like that," she said. "It was sort of happenstance. Sometimes we just get lucky."