Coral reef monitor adds new alert levels to keep up with soaring ocean temperatures

Ocean temperatures are rising so dramatically that the organization that monitors threats to coral reefs worldwide has added three new alert categories.

Coral Reef Watch is a program run by the U.S. National Oceanic and Atmospheric Administration that uses satellites and computer models to monitor heat risk to reefs.

Marine scientists and conservationists use the system’s data to understand the impact of warming temperatures on coral reefs, which are diverse marine ecosystems and a key indicator of ocean health.

“Unfortunately, last year got so hot in the wider Caribbean that our pre-existing alert system really was not doing a very good job reflecting just how severe the heat stress had gotten,” Derek Manzello, director of Coral Reef Watch, told As It Happens host Nil Köksal.

“With the new alert level system, this allows us to inform [conservation] managers and scientists as to what the anticipated impacts of these heat stress levels may be.”

What is coral bleaching?

Coral reefs are lush marine ecosystems that spring up around colonies of skeleton-covered invertebrates called hard corals.

Corals get their bright colours from algae that live inside their tissues. But when they become stressed, often due to temperature fluctuations, they expel the algae and turn bone white — a phenomenon known as coral bleaching.

Without its algae, the coral is extremely vulnerable to disease and starvation. If the algae doesn’t return, the coral will die — turning rich habitats into skeletal graveyards.

Coral reefs only occupy about one per cent of the ocean’s floor, Manzello says, but one in four documented marine species interacts them at some point in their life cycle.

“The coral reefs are the rainforests of the sea,” he said. “As coral reefs die, we’re losing this immense biodiversity.”

‘Risk of near-complete mortality’

Since it first launched in 2009, Coral Reef Watch has used two alert categories for monitoring heat risk to coral reefs — Level 1, which means reefs are at risk of coral bleaching, and Level 2, which means indicates the risk of “mortality of heat-sensitive corals.”

But in December 2023 — on the heels of a massive summer marine heatwave — the group added three more alert levels, which it unveiled publicly this month.

Level 3 indicates a risk of multi-species mortality for corals, Level 4 means more than half the corals in a reef could die, and Level 5 means “risk of near-complete mortality.”

“An alert Level 5 condition really represents the most extreme, worst-case scenario, that you could anticipate happening on a coral reef from heat stress,” Manzello said.

“This is analogous to a Category 5 cyclone or hurricane in that the impacts from an alert Level 5 bleaching event are expected to be severe and drastic.”

Before 2023, he says there were only three instances of heating at this level described in scientific literature.

That’s what happened to several reefs during the summer heatwaves of 2023, the effects of which were documented in a NOAA-University of Queensland study published in December.

The Sombrero Reef off the Florida Keys experienced 100-per-cent coral mortality in July 2023, according to the Florida-based Coral Restoration Foundation.

“This was, you know, devastating for people that had been spending years of their lives trying to restore these reefs,” Manzello said.

Impacts on humans

Stacy Jupiter, a marine scientist in Fiji for the Wildlife Conservation Society, welcomes the changes to Coral Reef Watch’s alert system.

“I believe the changes are necessary in order to demonstrate that the levels of heat accumulation experienced now around the globe are currently relatively greater than the highest alert levels previously issued,” she told CBC in an email.

While the Wildlife Conservation Society uses Coral Reef Watch’s alert system in his research, Jupiter says increased heat is just one of several predictors of coral bleaching.

Nevertheless, she says the degree of ocean warming in 2023 and 2024 has been “unprecedented in modern times” and “is, indeed, very concerning.”

Some can be explained by El Niño, a natural weather pattern that starts in the tropics, marked by part of the Pacific Ocean’s surface warming up.

“It is a little bit hard to say if we will continue to see the same elevated ocean temperatures in the coming years, but we can’t discount that we are approaching some tipping points in the Earth’s critical regulatory systems,” Jupiter said.

Manzello says there needs to be a lot more time and financial investment in coral reef protection, including the field of “assisted evolution,” in which scientists study the genetics of more heat-tolerant corals, and use that information “to breed corals for the future.”

If we don’t find innovative ways to preserve coral reefs, he says we’ll all feel the impact.

Coral reefs produce compounds used in medicine, provide habitat for fish that people eat, are a key component of tourism industries around the world and protect coastal areas from the impacts of powerful storms.

“In my mind, coral reefs are the most beautiful natural habitat that exists on planet Earth,” he said.

“The fact that these are just dying across a global scale every year, I think it’s really an ecological tragedy that’s unfolding right before our very eyes.”