Mission: Iconic Reefs
Relocates Thousands of Corals Amidst Record Heatwave

By Scott Atwell

August 2023

Thousands of corals, including some of the last known genotypes on the Florida Reef, have been relocated in a pair of rescue events organized by NOAA in response to record-breaking ocean temperatures in Florida Keys National Marine Sanctuary. The effort highlights two different adaptive management techniques: transferring coral fragments to land-based facilities and relocating in-water nurseries to deeper locations.

"The climate challenge may seem too big for individuals to make a difference, but these rescue efforts demonstrate otherwise," said Mission: Iconic Reefs co-lead Sarah Fangman, superintendent of Florida Keys National Marine Sanctuary.

Three people walking an ice cooler past a car.
MOTE Marine Lab workers arrive at Keys Marine Lab to stage the relocation of rescued coral fragments. Photo: NOAA
A small, horn-shaped coral on a disc being handed from one person to another.
A staghorn coral is transferred from a cooler to temperature-controlled raceways at Keys Marine Lab. Photo: NOAA

In late July, as rising temperatures began to bleach tropical corals at shallow reef sites and in-water nurseries, managers from NOAA and Mission: Iconic Reefs partners organized the herculean effort to collect replicates of all known living threatened elkhorn and staghorn coral fragments in Florida and transfer them to two land-based living gene banks for safekeeping. It was a high-stakes insurance policy, as NOAA's Coral Reef Watch four-month outlook predicts a 90% probability of bleaching heat stress for the months of August through November.

"The big problem we're facing is the length of time that these elevated temperatures are lasting," said Jennifer Moore, Mission: Iconic Reefs co-lead and NOAA Protected Coral Recovery program coordinator. "Prolonged high ocean temperatures induce bleaching, particularly at shallow reef depths of about 30 feet or less, and when corals are heat-stressed they are more susceptible to coral diseases — all of which can lead to death. Placing fragments of these unique genotypes in land-based living gene banks will ensure we do not lose these important corals."

a branching coral that is yellow to brown in color with white tips
This is a healthy two-year-old outplant of staghorn coral documented at Eastern Dry Rocks in July 2023. Photo: Katey Lesneski/NOAA
a branching coral that is pale yellow in color with white tips
This is a staghorn coral showing signs of paling, documented at Eastern Dry Rocks in July 2023. Photo: Katey Lesneski/NOAA
a branching coral that is mostly white in color
This is a staghorn coral documented at Sombrero Reef in July 2023 that is mostly bleached, with some segments that are dead and covered in a film of algae. Photo: Ananda Ellis/NOAA

Prior to outplanting corals on the reef, restoration practitioners nurture coral fragments at in-water nurseries located in ocean waters along Florida's Coral Reef where the renowned corals grow naturally. Genetic diversity is imperative for a healthy coral population, and currently only about 150 unique individuals of elkhorn and 300 of staghorn corals remain alive on Florida's Coral Reef — less than 1% of their former abundance. The rescue effort focused on 450 unique genotypes that did not already exist in land-based nurseries.

Mission: Iconic Reefs partners Coral Restoration Foundation, Reef Renewal USA, and Mote Marine Laboratory transferred the elkhorn and staghorn gene bank fragments to a staging site at Florida Institute of Oceanography's Keys Marine Lab in Layton, Florida. Rescued corals were held in temperature-controlled tanks before being loaded into the Coral Restoration Foundation's "coral bus" for shipment to The Reef Institute or transported to Mote's Gene Bank by The Florida Aquarium. Corals from nurseries at the University of Miami and Nova Southeastern University were also transferred to the two gene banks.

"These are the last remaining individuals left of the Florida population," Moore explained. Two copies of each genotype were sent to Mote's International Coral Gene Bank in Sarasota and The Reef Institute in West Palm Beach, where they will remain in perpetuity, hopefully unneeded.

A close-up of a clipboard with a list of various coral genotypes.
Coral technicians organizing fragments at a staging area before bussing them to other locations. Photo: NOAA
A woman holds a coral fragment in her hand while looking at others in a tank.
Cataloging coral genotypes is a vital component of the rescue. Photo: NOAA

Meanwhile, restoration partner Reef Renewal USA focused on an alternative solution: relocating 2,800 corals from its shallow Tavernier nursery to a deeper in-water location nearby where temperatures are reading 2 degrees cooler. Florida Keys National Marine Sanctuary mobilized its entire organization to meet an uncompromising deadline, permitting and installing nearly 100 new seafloor anchors in 70 feet of water to accommodate vertical ropes that suspend the growing coral fragments in the water column.

"Similar to how Goldilocks prefers the porridge that's neither too hot nor too cold, corals are picky animals," said Fangman. "It's a delicate balance between keeping the corals at their optimal temperature, and also making sure they are at the right depth in the water column with enough sunlight to get food through photosynthesis naturally."

A diver just under the water's surface and nearing a boat while holding a rope with coral fragments.
Reef Renewal's relocation first required the removal of vertical ropes from their shallow-water nursery. Photo: Florida Keys News Bureau
A rope holding coral fragments in the foreground with divers far below on the seafloor.
Temperatures at the deep-water nursery were as much as 2 degrees Fahrenheit colder than the shallow nursery. Photo: Florida Keys News Bureau

Relocating the corals to deeper water is only a temporary solution to help the corals escape the heat. As Fangman mentioned, most tropical corals need sunlight to thrive, and these particular corals are from shallower waters. The vertical ropes and trees will be returned to their original location when winter temperatures make it practical.

Mission: Iconic Reefs is one of the largest and most comprehensive coral restoration programs in history, supported by a myriad of partners and focusing on seven reefs in the Florida Keys: Carysfort Reef, Horseshoe Reef, Cheeca Rocks, Sombrero Reef, Newfound Harbor, Looe Key Reef, and Eastern Dry Rocks.

"This unbelievable collaboration is a forward-looking approach that aims to ensure the preservation of coral diversity and resilience for the future," said Moore. "While we remain hopeful that Florida Keys reefs can survive the current heat event, rescued corals will serve as broodstock for propagation in the event of a large-scale mortality event."

Scott Atwell is the communications and outreach manager for Florida Keys National Marine Sanctuary

Coral Bleaching Fast Facts

  • High marine temperatures stress coral, which rely on algae living in their tissues to provide nutrients and make them appear colorful. Reef-building corals prefer a temperature range of 73–84 degrees Fahrenheit (23–29 degrees Celsius). A rise in temperature of just 1 degree can cause bleaching — where corals expel the algae and turn white.
  • Reef temperatures are averaging 90 to 93 degrees Fahrenheit. NOAA's Coral Reef Watch has declared Alert Level 2, the highest stress level, for the Florida Keys. Mild bleaching in Florida Keys National Marine Sanctuary has occurred annually since 2011.
  • Historical bleaching events: (1) 1998: First global event; (2) 2014–2015: Last severe bleaching event, with El Niño, natural phenomena that likely exacerbated heat wave impacts and temperature spike; (3) July 2023: Current marine heatwave and bleaching event started prior to onset of El Niño.
  • It can take several weeks of heat stress before corals pale and/or turn white. Higher-than-average warm water temperatures have been recorded since February.
  • Corals started paling and showing partial bleaching in early July.
  • Past coral paling to this degree in Florida Keys National Marine Sanctuary has usually occurred in early/mid August.
  • Just because a coral appears translucent or white, does not mean it is dead. A coral can remain in a bleached, yet living state. If a coral still has soft tissue, it may still be alive.
  • If bleaching persists for too long, the coral is at a higher risk for mortality.
  • When a coral dies, algae begins to grow over the dead coral's exposed skeleton.
  • Corals in shallow waters are most susceptible to bleaching, however, 2023 reports of paling corals have been documented at some reef sites at depths down to 60 feet.
  • Similar to when a human has a weakened immune system, when corals experience heat stress, they are more prone to acquiring diseases.
  • The Mission: Iconic Reefs field team will survey all seven reefs during a research expedition August 11-19, during which a comprehensive bleaching assessment will be conducted.

How You Can Help

  • Recreational, commercial, and scientific divers are encouraged to become part of the BleachWatch Observer Network by participating in a training session. For more information, please contact taylor.tucker@floridadep.gov.
  • Recreational and professional divers and snorkelers in the Keys can get involved with BleachWatch by attending an upcoming training session led by Mote Marine Lab on August 12 at 10:00 a.m. Pre-registration is requested.

Flower Garden Banks National Marine Sanctuary Update

  • As of today, no bleaching has been observed in the East or West Bank.
  • A new real-time buoy at East Bank is helping to track temperature conditions both at the surface and reef depth.
  • Because the Flower Garden Banks reef in the Gulf of Mexico is deeper than reefs in Florida, temperatures at this time remain below bleaching levels. If temperatures continue to increase in August, bleaching will be expected.