Over the past 40 years, nearly 90 percent of live corals on reefs in the Florida Keys have been lost. Worldwide, tropical coral reef coverage has declined by 30% to 50% since the 1980s as climate change raises temperatures, sea levels, and ocean acidity. Authors of a recent study predict catastrophic effects on coral reefs throughout the world from an increase of 1.5 degrees C above pre-industrial levels.

Those corals will be missed. These ecosystems cover less than 1 % of Earth’s surface, but they feed and shelter more than a quarter of all marine fish species, as well as many other marine animals.

According to the International Union for the Conservation of Nature (IUCN), coral reefs directly support more than 500 million people, providing food, coastal protection, and livelihoods earned from fishing and tourism. Mote Marine Laboratory in Sarasota, Florida, reports that the reefs running some 350 miles from the Dry Tortugas to St. Lucie Inlet contribute $8 billion to the state’s economy through tourism, fisheries, and protection from severe storms. Mote scientists are joining experts around the globe to try and restore these ecosystems. One such project, the Florida Keys National Marine Sanctuary’s  “Mission: Iconic Reefs,” aims to restore seven reefs, one of the largest such efforts in the world. The organizations conducting in-water restoration work for the project’s first phase include Coral Restoration Foundation (CRF), Mote, and Reef Renewal.

Photo essay

Bleached brain coral (Pseudodiploria strigosa). This symmetrical coral grows in shallow parts of the Caribbean Sea and off the coasts of the Bahamas, Bermuda, Florida, and Texas. One way climate change affects coral reefs is that it causes a process called bleaching. Coral reefs are colonies of thousands of individual polyps, tiny animals that rely on symbiotic algae for 80% of their nutritional requirements. At temperatures above their preferred range, corals become stressed and expel their algae. The coral skeleton then appears white, or bleached, as seen here. If temperatures soon enough drop back to normal, the algae may grow back. If not, the coral eventually starves.
The bright whiteness of this coral is an obvious sign of bleaching. The first documented global bleaching event – defined as bleaching affecting reefs in the Atlantic, Pacific, and Indian Oceans within the same year – occurred from 1997 to 1998, killing at least 15% of reefs worldwide. Another event, from June 2014 to May 2017, affected more than 70 percent of the world’s reefs, and IUCN reports bleaching occurred each year from 2019 to 2021. In 2021, the world’s oceans were the hottest ever recorded and latest research shows increasing frequency, magnitude, and persistence of extreme marine heat events.

Florida reefs also face a number of other threats, including disease outbreaks and storms, made worse by climate change. In fact, coral reefs overall are one of the most threatened ecosystems on Earth.

NOAA’s “Mission: Iconic Reefs” restoration program raises corals in nurseries and plants them on damaged reefs. Here, divers with CRF attach fragments of staghorn corals (Acropora cervicornis) to Coral Trees™, simple PVC structures that CRF developed to grow large numbers of fragments in offshore nurseries. Fragmentation is a form of asexual reproduction (corals also reproduce sexually through spawning): A branch of coral that breaks away can reattach to a reef and begin to grow a new colony if conditions are favorable. CRF currently tends seven offshore Coral Tree Nurseries along the south Florida coast, where it grows more than 20 different species.
Once fragments on coral trees grow large enough, divers tag them and attach them directly to existing reefs using a non-toxic marine epoxy, a process called outplanting. Coral restoration efforts are not without their critics. “We have received criticism for launching this mission from very respected scientists,” says Sanctuary superintendent Sarah Fangman. “Yes, we’re doing this work in the midst of ongoing rising temperatures and intense storms. But I don’t believe we have the luxury of waiting. We have to address temperature stress and water quality issues and, to give this system a chance, help it along while we’re fixing those things.”
Since 2012, CRF has out-planted more than 170,000 corals onto Florida reefs, including this elkhorn. Scientists also are studying coral genetics to better inform restoration work. “We believe you have to sell some hope,” says Mike Echevarria, founder of Reef Renewal. “We have people say all the time, why bother, it isn’t going to work. But there is a lot or research on genetics, heat tolerance, and selective breeding.” For example, authors of one study recently found that corals exposed to a stressful temperature treatment in the laboratory for 90 days were more tolerant to increased water temperatures.
Staghorn and elkhorn coral (Acropora palmata), shown here, are listed on the IUCN Red List of Endangered Species as “Critically Endangered.” Researchers at Mote are among those working to identify native genetic coral varieties that are resistant to stressors such as increased water temperatures. The lab has planted more than 100,000 corals, including genetic varieties of staghorn and elkhorn that are offspring from strategic breeding of native parent corals. This approach helps maintain genetic diversity, which increases the resilience of the reefs.

Melissa Gaskill is an Austin-based science writer who frequently covers climate change and ocean issues. Photos: Courtesy of Brandon Cole Marine Photography.