“The global coral reef heat stress monitor has been forced to introduce new alerts as temperatures continue to rise, with some areas experiencing unprecedented levels of heat stress.”
The primary mechanism for signaling the threat of heat-induced strain on the Earth’s coral reefs has been compelled to incorporate three additional warning levels to account for continuously rising temperatures.
The US government’s Coral Reef Watch program has implemented alterations following a surge in heat stress that caused widespread bleaching and coral deaths in reefs across the Americas last year.
“We are entering a new world in terms of heat stress where the impacts are becoming so pervasive that we had to rethink how we were doing things,” the Coral Reef Watch director, Dr Derek Manzello, told the Guardian.
Coral reefs are facing a high risk of damage from rising global temperatures, caused by the burning of fossil fuels and deforestation. They also serve as habitats for approximately 25% of the world’s marine species.
High temperatures can lead to corals becoming disconnected from the small algae that provide them with their distinctive color and a significant portion of their nourishment. While bleaching can result in coral death, researchers state that even those that manage to survive are at a greater risk for illness and have difficulty reproducing.
The National Oceanic and Atmospheric Administration’s Coral Reef Watch used to release warnings for coral reefs in four levels. The second level, alert level 2, indicated a high likelihood of “severe bleaching and significant mortality”.
The program has now included three additional warning levels to a tool utilized by researchers, environmentalists, and volunteers worldwide to comprehend the challenges confronting coral reefs in their regions.
At the core of the alert system is a gauge of the level of accumulated heat stress experienced by corals at a particular moment, referred to as degree heating weeks.
For instance, if corals are exposed to temperatures that are 1 degree Celsius above the typical maximum for a duration of seven days, then 1 DHW (degree heating week) will accumulate.
The previous system used by Coral Reef Watch assigned the highest rating to temperatures of 8 DHWs or higher. However, during the summer of the last year in the northern hemisphere, extensive sections of reefs in multiple countries experienced extreme heat stress that exceeded this highest rating, reaching over 20 DHWs in certain areas.
“We began to question the implications of these extreme conditions on the ecosystems,” stated Manzello. “Did reef managers require additional information for managing such extreme situations?”
Our previous product lacked crucial information and failed to accurately reflect the severity of the situation.
“We understand that the decline of coral begins at approximately eight weeks of exposure to higher temperatures, and we are now observing catastrophic levels of more than 20 weeks of high temperatures.”
If you surpass a DHW value of 20, it can be compared to a Category Five cyclone, resulting in exceptionally severe and destructive consequences. This is considered the most extreme situation possible.
The new alert system from Coral Reef Watch categorizes DHWs (degree heating weeks) into three levels: level 3 for values between 12 and 16, level 4 for values between 16 and 20, and level 5 for values above 20.
The attached text for the warning levels has been modified to indicate the varying levels of severity for bleaching and the potential for coral death, based on their sensitivity to heat.
At level 5 of alert, the caution declares a possibility of “almost total loss of life” for all coral reefs.
The warning system had not been altered since its inception in 2009 until the recent changes were implemented just before Christmas. The fundamental beliefs regarding the potential dangers associated with varying levels of heat stress had been established since 1997.
Dr David Wachenfeld, who leads research on reef ecology and monitoring at the Australian Institute of Marine Science and is a former chief scientist at the Great Barrier Reef Marine Park, said Coral Reef Watch was the “go-to” tool for the global coral reef community.
He stated that the occurrences during the summer in the northern hemisphere last year were undoubtedly exceptional.
“The level of thermal stress experienced was unparalleled. I applaud NOAA for their swift response and recognition that our current system, established in the late 20th century, is inadequate for describing the extreme conditions observed in the early 2020s.”
According to Wachenfeld, the warning levels are a useful indicator, but reefs may respond differently to equal amounts of heat stress based on the variety of species present or the past occurrences of bleaching in that particular area.
“Making necessary adaptations to our systems is an unavoidable result of the changing climate,” he stated. “We are currently facing unknown challenges in regards to the effects of increased heat on reefs.”
The head of oceans at WWF-Australia, Rickard Leck, stated that the new system demonstrates the extreme levels of ocean temperatures and the threats to coral reefs. This serves as a strong reminder that the effects of global warming are currently and significantly affecting our oceans, in ways that were not predicted just ten years ago.
Tracy Ainsworth, who holds the position of vice-president at the International Coral Reef Society, stated that heat stress events were uncommon ten years ago. However, the current situation involves not only bleaching events, but also mortality events – a significant shift from the past.