For the first time, biologists have caught a rare type of coral in the act of reproducing, and they were able to collect its sperm and eggs and breed the coral in the laboratory. The success is part of an effort to stem the decline in many types of coral around the world. To understand how this works, you need to know that coral reefs are actually colonies of tiny organisms encased in hard skeletons. In many kinds of coral, the whole colony reproduces at once, in a spectacular event called “broadcast spawning.” Males eject clouds of sperm into the water, and then females do the same with eggs. The sea creatures cross their fingers (or whatever the coral equivalent of that is) and hope for the best. Scientists have observed this sort of thing before, but not with pillar coral, a rare type found in the western Atlantic and Caribbean that forms columns, or pillars. Marine biologist Kristen Marhaver, of the University of California, Merced, says that’s because the researchers’ timing was off. “For years, scientists were underwater about 30 minutes after the pillar coral spawned,” she explains.
They were late in those expeditions because they were focusing on a different type of coral — elkhorn. As it turns out, elkhorn coral spawns just after the pillar coral does. Typically divers were still suiting up for the elkhorn spawning, Marhaver says, when the pillar coral was busy reproducing beneath their boat — and the divers would miss the pillar coral action completely. Three years ago, Marhaver and colleagues — with a group called Caribbean Research and Management of Biodiversity, on the island of Curacao — figured that out. Eventually they nailed down the pillar coral’s mating moment. The moment came “three days after the August full moon, 100 minutes after sundown,” she says. So the next time they spawned, Marhaver was in the water waiting, and saw what looked like a cloud rising from the reef. “They’re very flamboyant,” she says, “it’s quite obvious what they’re up to.”
The divers frantically collected sperm and eggs. “You’re running around underwater with flashlights and tarps and doing hand signals and (carrying) collection tubes,” Marhaver says. “It’s beautiful to see. We scream through our scuba regulators and snap millions of photos and breathe our air tanks down really fast.” First in the water, and then back at the lab, the team fertilized the eggs with the sperm. They were able to raise embryos up to the juvenile stage — a first for pillar coral. Marhaver and her colleagues describe all this in the current issue of the journal BMC Ecology. She says eventually, the goal is to return these juvenile corals to the ocean and get them to thrive. Pillar coral isn’t doing well on its own — it’s very hard to find juveniles at all– and scientists don’t know exactly why.
“Bringing them together in the lab is a little bit like spiking the sauce,” Marhaver says, “ensuring the gametes meet. And then we can put them back underwater and say, ‘OK, now do your thing.’ ” Corals have been “doing their thing” for millennia. But Kim Beach Ritchie, a marine biologist at the Mote Marine Laboratory and Aquarium in Florida, says the creatures are “incredibly sensitive to both temperature changes and storm damage.” They don’t like surprises, he says. These days, surprises include water that’s warmer and more acidic from climate change and pollution. The acidity increases as the ocean absorbs the extra carbon dioxide that’s in the air now from the increased burning of fossil fuels. Acidic water is especially bad for animals, like coral, that draw chemicals out of seawater to make their shells or external skeletons.
Ritchie is part of a team of scientists from academia and the National Oceanic and Atmospheric Administration that’s written a plan to help coral in U.S. waters survive these changes. Many now are not — they’re dying. Aside from breeding coral, Ritchie says, scientists are trying to identify strains that are resilient, and then put them back in the ocean. You take eggs and sperm from any coral and then rear them under challenging conditions in the laboratory, she says, “and see which ones make it.” The creatures that do survive would, theoretically, have a better chance of thriving back in the sea.