DRY TORTUGAS NATIONAL PARK — Nearly three dozen young lab-grown elkhorn corals, including a group of experimental hybrids known as 'Flondurans,' were outplanted onto reefs in Florida’s Dry Tortugas National Park in spring 2025. This marked the first time Flonduran corals—cross-breeds of Florida and Honduran elkhorn corals—were introduced to the park as part of a climate resilience experiment.
The outplanting effort aims to test whether hybridizing Florida’s elkhorn corals with more heat-resilient Caribbean variants can help the species survive rising ocean temperatures. In April 2025, scientists and divers transported two-year-old corals—half Flonduran and half from Florida parent colonies—to Dry Tortugas, where they were attached side by side on cinder blocks at multiple reef sites.
Elkhorn corals once formed complex reef structures throughout Florida and the Caribbean, providing habitat for marine life and buffering coastlines from waves. However, an unprecedented marine heatwave in mid-to-late 2023 triggered mass bleaching that killed nearly all remaining elkhorn colonies in Florida. "Almost every single elkhorn coral that was still alive on Florida’s coral reef died," said Keri O’Neil, senior scientist and director of the Coral Conservation Program at The Florida Aquarium in Apollo Beach. Scientists have determined that elkhorn corals are functionally extinct in the Florida Keys and Dry Tortugas.
Following the die-off, University of Miami marine biologist Andrew Baker began sourcing genetic material from a resilient elkhorn reef in Tela Bay, Honduras, known locally as a 'rebel reef.' There, corals thrive despite warm, nutrient-rich waters affected by agricultural runoff. In 2024, Baker led a team that collected Honduran elkhorn colonies and, in collaboration with Keri O’Neil of The Florida Aquarium, performed the first controlled cross-breeding between Florida and Honduran corals in U.S. laboratories. Researchers collected eggs and sperm from Florida and Honduran elkhorn corals during controlled spawning events and fertilized them in laboratory tanks. This process produced the first generation of 'Flonduran' corals.
"We have to incorporate as much of the genetic diversity in the species as possible to try to find the corals that will live through climate change," said Keri O’Neil. In 2024, 35 Flonduran coral colonies were outplanted off the coast of Miami near Key Biscayne. Many of those corals still appear to be doing well.
"These babies have been raised on land since conception," said Bailey Marquardt, a doctoral student at the University of Miami Rosenstiel School of Marine, Atmospheric and Earth Science. "There’s a lot of anticipation around how these corals will perform," she said. "If it turns out that these corals are no more heat resistant than Florida’s, that means we kind of have to go back to the drawing table." Marquardt is leading a broader effort to plant at least 300 more elkhorn colonies across Florida, starting in Dry Tortugas.
"This is a critical step in field-testing measures to help reefs adapt to increased ocean temperatures," said Andrew Baker, professor at the University of Miami’s Rosenstiel School. "By testing these Flonduran and Floridian corals side-by-side on different reefs, we can begin to identify suitable source populations for future breeding efforts." Scientists will monitor the corals’ growth and survival over the coming months during what is expected to be a very hot summer.