Heatwaves might be associated with wildfires, heat stroke, and damaged crops on land, but what happens when they occur in the marine world? Fish flee poleward to cooler waters, toxic algae proliferate, and once vibrant coral becomes stripped of color and life. And things are only set to get worse.
A new study published in Nature Climate Change is the first to systematically measure and compare the impacts of marine heatwaves – when extreme temperatures are maintained for five days or more – across the globe.
Analyzing data from over 1,000 studies, the researchers found that marine heatwaves have increased by more than 50 percent since the mid-20th century, and are becoming more severe, prolonged, and frequent, a pattern that is having detrimental impacts on carefully balanced ocean ecosystems and marine life.
"Globally, marine heatwaves are becoming more frequent and prolonged, and record-breaking events have been observed in most ocean basins in the past decade," lead author Dan Smale, a researcher at the Marine Biological Association in Plymouth, UK, told AFP.
"Just as atmospheric heatwaves can destroy crops, forests and animal populations, marine heatwaves can devastate ocean ecosystems."
Between 2013 and 2016, a marine heatwave wreaked havoc off California’s coast causing sea temperatures to rise by 6°C (10.8°F). Ominously nicknamed “The Blob”, it led to the closure of fisheries and caused whales, sea lions, and seabirds to starve as the plankton they depend on perished in the heat.
In addition to harming sea life, marine heatwaves impact us by damaging the fisheries that 56 million people worldwide rely on for food or employment. In fact, research published last week found that fishing losses due to climate change are as high as 35 percent in certain regions such as the North Sea and East China Sea.
“We were stunned to find that fisheries around the world have already responded to ocean warming,” Dr Malin Pinsky, an ecologist at Rutgers University, said in a statement last week. “These aren’t hypothetical changes sometime in the future.”
Another significant victim of ocean heatwaves is coral. Often described as the rainforests of the sea, coral reefs are home to a plethora of creatures, from tiny crustaceans and bizarre-looking nudibranchs to colorful parrot fish and blacktip reef sharks. Thanks to ocean warming, half of the coral in the northern Great Barrier Reef has died since 2016, and it probably won’t recover.
Along with coral reefs, marine heatwaves damage kelp forests and seagrass beds, both of which form the bases of important ecosystems. Kelp forests supply shelter to shellfish, fish, and marine mammals like sea otters and gray whales. Meanwhile, turtles, dugongs, and even sharks snack on seagrass, which also acts as an important carbon store.
“Carbon stored by sea grasses and mangroves may be released if they are hit by extreme temperatures," warned Smale.
The new research adds to the overflowing pile of evidence that shows human-induced climate change is having disastrous consequences on the environment, harming the resources on which we depend.
“Given the confidence in projections of intensifying extreme warming events with anthropogenic climate change, marine conservation and management approaches must consider marine heatwaves and other extreme climatic events if they are to maintain and conserve the integrity of highly valuable marine ecosystems over the coming decades,” the study’s authors conclude.