Florida Keys coral reefs devastated by 2023 heat wave
A new survey reveals extensive damage to Florida Keys coral reefs caused by a severe marine heat wave in 2023.
Extent of Damage
A recent survey conducted on Florida Keys coral reefs shows significant damage resulting from a long-lasting and severe marine heat wave that occurred last year. Corals are crucial for biodiversity, providing shelter for over 25% of ocean animals and driving fishing and tourism revenue. These coral reefs are increasingly threatened by climate change, putting their viability at risk.
Preliminary results demonstrate that less than 22% of the approximately 1,500 staghorn corals surveyed are still alive. Out of the five reefs surveyed by NOAA's Mission: Iconic Reefs program and the Mote Marine Laboratory and Aquarium, only Carysfort Reef and Horseshoe Reef, the two most northern ones, still had living staghorn coral. Live elkhorn coral was only found at three of the surveyed sites, with no living staghorn or elkhorn corals found at Looe Key Reef in the lower Florida Keys.
Impact of Warm Water
Warm water corals thrive within a specific temperature range. When the water becomes too warm, corals expel the algae living in their tissues, causing them to turn white in a process known as coral bleaching. Bleached corals are more vulnerable to further heat stress, including eventual mortality if the extreme temperatures persist. Last year's marine heat wave resulted in more severe and prolonged coral mortality than usual for the Florida Keys.
Katey Lesneski, monitoring coordinator for NOAA's Mission: Iconic Reefs program, reports that out of the roughly 30,000 staghorn coral outplants planted between 2020 and 2022 in these five reefs, the one-year survival rates ranged from an average of 40% to over 75%. 'Outplanting' refers to planting coral fragments grown in nurseries back onto reefs.
Conservation Efforts
Scientists at NOAA, Mote, universities, and other institutions made significant efforts to save corals and preserve conservation gains in the Florida Keys. Measures included removing corals from the hot seas and relocating them to nurseries on land, subsequently re-planting them once water temperatures cooled. However, these extreme conservation measures may not be viable in the future if marine heat stress becomes more common, severe, and long-lasting according to climate projections.
NOAA's Coral Reef Watch program has added three new alert categories and colors in response to the 2023 marine heat waves. The highest category, Bleaching Alert Level 5, represents a risk of 'near complete mortality.' Last year experienced intense marine heat waves globally due to the combination of long-term climate change and the El Niño climate cycle, resulting in record-high ocean heat content.
