Sea life at risk from marine heatwaves

Heatwaves affecting oceans are becoming more frequent — and wreaking havoc on marine ecosystems, scientists have warned.

Heatwaves are impacting the world’s marine ecosystems, scientists have warned. Picture: Supplied

Heatwaves affecting the world’s oceans are becoming more frequent — and wreaking havoc on marine ecosystems, scientists have warned.

A marine heatwave is said to have taken place when sea temperatures are significantly higher than usual for at least five consecutive days. The most comprehensive study of the phenomenon to date found that these abrupt, localised spikes in ocean temperatures had increased in severity and frequency over the past three decades.

There were 54 per cent more marine heatwave days per year between 1987 and 2016 than there had been between 1925 and 1954.

“Extreme temperature events may be one of the most important stresses on the oceans in coming decades,” said Dan Smale of the Marine Biological Association of the United Kingdom, who led the research. “Whether it’s seaweeds or corals, fish, seabirds or mammals, you can detect the adverse effects of marine heatwaves,” he said.

Rapid rises in sea temperatures were found to have had an especially serious impact on foundation species such as corals, seagrasses and kelps, researchers said. These organisms serve as pillars of marine ecosystems, providing food and protection from predators and helping to regulate sea temperatures.

Abalone stocks off the Australian coast have been affected. Picture: Robin Sharrock

Some, such as sea grasses, store significant amounts of carbon, potentially helping to guard against climate change. When they disappear, a large number of other species tend to follow. The effects are felt by humans as fisheries decline, the authors of the study warned.

Marine heatwaves were “emerging as forceful agents of disturbance”, they added, which had the potential to “restructure entire marine ecosystems”. The research, published in the journal Nature Climate Change, included an examination of eight prolonged marine heatwaves, including “the Blob”, a vast mass of warm water that lingered off the west coast of the United States from 2014 until 2016. At its peak, the Blob covered about 3.5 million square miles, reaching from Mexico to Alaska. It was linked to toxic blooms of algae, volatile shifts in food chains and mass die-offs of species such as sea otters and humpback whales.

Other events reviewed in the paper included a marine heatwave off Western Australia in 2011, which devastated abalone stocks. A heatwave in the Atlantic, off the United States, in 2012 forced lobster stocks north towards cooler Canadian waters.

A separate study published in the journal Science suggested that global fisheries production had declined by 4 per cent between 1930 and 2010, due to climate change and “weather-related factors”, with some of the largest fish-producing regions experiencing losses of up to 35 per cent.

The Times