They’re living boulders on the ocean floor. Northeastern research explains the mysterious corallith by Cynthia McCormick Hibbert July 26, 2024 Mark Patterson, a professor at Northeastern University’s Marine Science Center, studied hundreds of coralliths off the coast of the Florida Keys. Waves generated by increasingly strong hurricanes and tropical storms have laid waste to endangered coral reefs by smashing coral branches and overturning colonies. But an oddball type of free-living coral actually thrives on the energy generated by storms. Called a corallith, it is known as the rolling stone of the shallow ocean floor. Coralliths occur when the tumbling motion of wave energy shapes coral into spheres that can grow to be nearly 1.4 meters in diameter, at least in the Florida underwater living boulder field studied by Mark Patterson, a professor at Northeastern’s Marine Science Center. “That’s ginormous,” Patterson says. Imagine a sphere of coral twice the width of an inflated exercise ball, weighing a couple of tons and existing for 100-120 years. Hundreds of these coralliths — large and small — are living on the sandy seabed off Plantation Key in Islamorada, Florida. Patterson says they are the oldest and largest coral formations of this type ever discovered. Don’t expect to find coralliths rolling around like tumbleweeds. An expert in both coral and microfluidics, Patterson calculated in a paper published in the Bulletin of Marine Science that “once every seven years was how frequently you had to have a big storm to roll the big ones.” “When they get rolled, it’s just enough to turn over. And then enough sand gets jammed in, to stop the rolling. It’s not like they’re going back and forth” all the time, he says. As a scientist who has studied the devastating impact of climate change on coral reefs, Patterson finds the formation of coralliths an amazing adaptation to tempestuous conditions. “There have always been waves on this planet,” he says. “This is probably a really ancient way of coping with what storms do to animals in shallow water.” “They have to take what Mother Nature dishes out. They don’t always get killed—they can adapt and do this marvelous thing of turning into a living sphere.” What we think of as a hard coral reef or corallith is formed when tiny, cup-shape polyps secrete a skeleton of calcium carbonate. The layers and layers in big reefs can be seen from space. In the case of coralliths, the polyps that are sitting on the sand probably retract and die, Patterson says. When a storm comes along, it kicks the colony over and the colony extends its tissue to the dead areas, Patterson says. “The coral is going to grow over that and start growing again, which is pretty cool. It’s a magical process occurring at the scale of microns,” he says. “It seems like if conditions are right, corals can do this worldwide,” he says. Coralliths need sunlight and currents to grow larger, both of which are in ample supply in the clear, shallow waters off Plantation Key and in the storms that frequent Florida. An aerial photo of the corallith field off the Keys depicts dozens of the rotund coral colonies right off shore, near homes and buildings. “They’re living in a sandy environment in the shallows where there’s enough wave energy to turn into rolling stones, living rolling stones of the sea,” Patterson says. The Florida coralliths have been surveyed extensively by paper co-author William F. Precht, an expert on coral bleaching, who Patterson estimates has done thousands of dives in the area. Patterson says he came into the picture as an expert in environmental fluid mechanics with a joint appointment in engineering. He says Precht and co-author Peter W. Glynn asked, “Can you calculate how much force it would take to roll one of these coralliths and translate that to what the waves would have to be like?” “Storms are becoming more frequent and more powerful in the tropics,” Patterson says. “In theory, the increased wave action can make coralliths bigger.” Researchers say the return time for a tropical storm or hurricane powerful enough to roll big coralliths and help them maintain their spherical shape is one in seven years. But climate change-related damage such as erosion and bleaching — the bane of coral reefs — can make coralliths more fragile and more likely to crumble during big storms. “Then it’s game over,” Patterson says, whether the corallith was a 120-year behemoth or a basketball-sized 7-year-old Studying the giant mobile coralliths off the Florida Keys was a fun application of physics and engineering, he says. “That said, I’m perpetually depressed that this is the first major ecosystem on the planet that may go functionally extinct during the lifetime of my grandkids,” Patterson says. “A lot of reefs are just a shadow of their former selves.” Corals provide habitats for fish and food for local communities, protect coastlines from storms and offer snorkelers and scuba divers plenty of recreational opportunities. Whether living in reefs or calcified spheres, corals “are of incalculable value,” Patterson says. Cynthia McCormick Hibbert is a Northeastern Global News reporter. Email her at c.hibbert@northeastern.edu or contact her on X/Twitter @HibbertCynthia. Enjoyed the story? Get NGN Magazine in your inbox. Name: Email: Comment: EmailSubscribeReader TypeWorld NewsUniversity News Developed by Hannah Moore, Court Smith, and Xristopher AndertonIllustrations by Renee Zang/Northeastern UniversityAdditional imagery provided by Mark PattersonSlide 2 imagery provided by Velvetfish via Getty ImagesSlide 10 imagery provided via Google EarthSlide 12 imagery provided by Zenobillis via Getty ImagesSlide 13 imagery provided by Rainer von Brandis via Getty Images Loading…