KEY BISCAYNE — University of Miami scientists transported 30 pieces of elkhorn coral from offshore nurseries to a land-based hatchery on Wednesday. The operation moved genetically distinct coral fragments to a controlled environment on Key Biscayne to shield them from dangerously high ocean temperatures.

Elkhorn coral populations in Florida are considered functionally extinct, meaning remaining colonies are too small and far apart to reproduce successfully in the wild. The 30 coral pieces represent 30 different genotypes of elkhorn coral, preserving a wide range of genetic material for the critically endangered species.

The coral pieces were collected from nurseries located off the Florida coast, spanning from Broward County to the Lower Keys. Divers wrapped each coral piece in wet bubble wrap, placed them in coolers, sanitized them, and put them in tanks at the hatchery. Researchers moved the corals to holding tanks as a stopgap measure until ocean temperatures cool in the fall, at which point they plan to return them to offshore nurseries.

Some elkhorn coral were left in the offshore nurseries to monitor how they fare during the summer. This split approach allows scientists to gather data on resilience while protecting a significant portion of the remaining genetic stock. The University of Miami exchanges coral with other researchers and facilities to preserve genetic diversity across different regions.

"Today was lessons learned, many of you remember the 2023 bleaching event where there was devastating loss of coral species and we recognized that we have to be more proactive because this would happen again," Dalton Hesley said. Hesley is a coral expert with the Rosenstiel School of Marine, Atmospheric and Earth Science at the University of Miami.

"So these are the last of the wild populations that we know in South Florida, meaning that we collected small pieces years back, and maintained them and gardened them but their parents, the ones we initially collected from, are likely gone," Hesley added. He emphasized the urgency of the current conservation efforts given the status of the original wild colonies.

Diego Lirman is an associate professor of marine biology at the University of Miami and a senior researcher at the Rosenstiel School. He noted the rapid succession of environmental stressors affecting the reef systems in recent years. "They seem to be blending into each other and corals are not getting time to recover," Lirman said. The lack of recovery time between heat events prevents the coral from rebuilding energy reserves needed to survive subsequent stress.

The hatchery, located at the University of Miami’s experimental reef facility on Key Biscayne, provides filtered seawater, controlled temperatures, and consistent monitoring. These conditions reduce the risk of disease and thermal stress during the peak of summer. The facility has previously served as a refuge during extreme heat events and hurricanes.

Elkhorn coral (Acropora palmata) is a foundational reef-building species that once dominated shallow Caribbean waters. It provides critical habitat for fish and helps buffer shorelines from storm surges. However, due to climate change, disease outbreaks, and ocean acidification, its populations have declined by more than 95% since the 1980s.

Restoration efforts led by the University of Miami and partners in the Coral Restoration Consortium involve growing coral fragments in nurseries and outplanting them to degraded reefs. The current relocation is part of a broader strategy to safeguard genetic lines while improving survival rates through assisted evolution and selective breeding.

Water temperatures across South Florida have exceeded 30°C (86°F) in recent weeks, approaching the thermal threshold for coral survival. NOAA’s Coral Reef Watch has issued a level 3 bleaching alert, the highest on its scale, indicating imminent or ongoing mortality.

Scientists stress that while short-term interventions like relocation are essential, long-term coral survival depends on global action to reduce greenhouse gas emissions and mitigate climate change.