"There's Not Much Hope": Mediterrenean Corals Collapsing Under Relentless Heat
For years, Joaquim Garrabou donned scuba gear and dove into the waters of the Scandola Marine Reserve in Corsica to find a paradise. Twenty meters (66 feet) beneath the surface, there were reef walls draped with soft red coral (Corallium rubrum) and red gorgonian sea-whips (Paramuricea clavata), all swarming with fish and other sea creatures. But in 2003, a marine heat wave hit Scandola, leading to the death of many coral reefs. More than 15 years later, the reefs have still not recovered.
Now when Garrabou dives at Scandola, he’s greeted by the skeletons of once-thriving corals. “It’s like seeing someone who is ill, who has a disease that you cannot find the solution for,” Garrabou told Mongabay in a video interview. “You hope that someday there will be a [solution] but you see that there’s not much hope.” After the 2003 marine heat wave, Garrabou and colleagues began monitoring Scandola’s coral reefs to track their recovery. But after accumulating reef survey data and temperature data over many years, they eventually realized they were actually tracking the reefs’ collapse. The results of their long-term study were recently published in Proceedings of the Royal Society B.
“We knew something bad was happening to the corals around the world, but we weren’t expecting a collapse in all of the populations that we studied,” study lead author Daniel Gómez-Gras, a marine ecologist at the Institut de Ciències del Mar in Barcelona, told Mongabay in a video interview. “The point of tracking these populations for such a long time was to show recovery in the long term because we expected that the populations — maybe not in five years, but in 15, 20 years — [would be] able to recover. However, we saw a collapse.”
The data showed that marine heat waves were happening every year in different parts of the Mediterranean between 2003 and 2018. For 12 of those years, the water temperature at a depth of 20 m reached more than 23° Celsius (73.4° Fahrenheit), which is considered a sublethal threshold for corals. And for four of those years — 2009, 2016, 2017 and 2018 — temperatures at that depth breached the lethal threshold for corals at 25°C (77°F). The researchers found that the ceaseless heat wasn’t allowing these slow-growing coral reefs to recover. “Frankly, I never thought that I would be seeing it,” Garrabou said. “And it’s happening really fast.”
EDIT
https://news.mongabay.com/2022/02/theres-not-much-hope-mediterranean-corals-collapse-under-relentless-heat/
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