Florida Aquarium researchers were watching knobby cactus corals earlier this month when someone made a perplexing discovery.

A stray “settler,” or coral larva, had landed on a small ceramic tile and morphed into a primary polyp, the start of what might become a full-fledged colony. Corals, despite their appearance, are animals, not plants, with mostly minuscule polyps forming groups that combine in diverse reefs. The larva was evidence of birth — a breakthrough for the cadre of scientists devoted to helping coral reproduce under human care. They just didn’t know what kind.

The settler had not come from the knobby cactus, and the researchers had no idea which of the corals they studied was responsible. They used bucket-like collectors to trace more larvae to something that looks to the naked eye like a rocky brain, in laser-show hues of green, purple and red.

The ridged cactus coral, relatively uncommon but striking in its beauty, had reproduced in a lab for what the aquarium says is the first time. More than a week later, two corals are still making larvae, said Keri O’Neil, senior coral scientist.

“We’ve had 349 little babies made over nine days,” she said Tuesday.

Ridged cactus coral seen at The Florida Aquarium’s Center for Conservation in Apollo Beach. [ The Florida Aquarium ]

The team has recorded the process on video, but before this month knew little about the reproduction of corals like the ridged cactus. Aquarium staffers could find only one master’s thesis, thin on details, from the year 2000.

“Basic things about these species we know nothing about,” O’Neil said. The scientists have no clue, for instance, how long the corals will put out larvae. “For all we know they do it all year long and we just didn’t catch it before.”

Aquarium leaders say they have now reproduced eight species of coral at their Center for Conservation. The effort is rooted in crisis. From St. Lucie Inlet to the Keys, the Florida Reef Tract is imperiled by warmer sea waters, acidification and Stony Coral Tissue Loss Disease, which has devastated the third largest barrier reef in the world, killing off corals so fully that scientists say it’s now even hard to find clean specimens for labs.

Coral barriers are pivotal for Florida, cutting the power of storm surges and waves that buffet the land and serving as a habitat for a teeming horde of marine life, cherished on the southern coast.

“If you don’t have a living reef, you don’t have the nursery grounds,” said Debborah Luke, Florida Aquarium’s senior vice president of conservation.

Scientists are still struggling to understand the disease, she said, even as it guts Florida’s reef, killing off polyps and leaving only the calcium carbonate they secrete, blanched coral skeletons as a testament to the toll.

The aquarium hopes to reproduce enough species in its greenhouses that researchers can one day replace lost colonies. Roger Germann, Florida Aquarium’s CEO and president, said the project has cost about $2.5 million over four years through a combination of government and private funding, including from ticket sales.

O'Neil said she has studied corals for two decades but humans have much to learn. Last August, the aquarium celebrated the reproduction of pillar coral, a key species found in local reefs.

Unlike pillar coral, the ridged cactus is a brooding reproducer not a broadcaster: Rather than issuing sperm and egg into the water, the ridged cactus releases only sperm, which fertilizes eggs inside the animals. The corals are simultaneous hermaphrodites, meaning both male and female at the same time, said biologist Emily Williams.

The larva from the ridged cactus was the biggest the scientists have seen yet, only a few millimeters at most, with spots and stripes and colors. Upon release, it looks like a shell tumbling away from the colony.

Ridged cactus coral larvae, as reproduced at The Florida Aquarium’s Center for Conservation in Apollo Beach. [ The Florida Aquarium ]

The new corals could be up to a couple of inches in size a year from now, large enough for researchers to start considering placement in the wild, O’Neil said. Ridged cactus corals do not get much bigger than the size of a dinner plate, she said, and live about 40 feet deep in water.

The parent corals came from the Florida Keys, according to O’Neil, in a rescue project led by the Florida Fish and Wildlife Conservation Commission and National Oceanic and Atmospheric Administration Fisheries.

A new reproduction would usually be celebrated in person, but with the coronavirus pandemic, scientists have worked in staggered shifts. They can’t risk having one sick staffer force everyone else into quarantine, O’Neil said, with no one to run the lab.

“Our corals don’t know what’s happening outside in the world,” she said.