Nature reports:

Ten years ago, dead fish began washing ashore on the beaches of Western Australia. The culprit was a huge swathe of unusually warm water that ravaged kelp forests and scores of commercially important marine creatures, from abalone to scallops to lobster. Over the following weeks, some of Western Australia’s most lucrative fisheries came close to being wiped out. To this day, some of them have not recovered.

After the crisis, scientists came together to assess the damage and try to understand what had caused the unusual warming. “This event really had such devastating consequences for marine ecosystems,” says Jessica Benthuysen, a physical oceanographer at the Australian Institute of Marine Science in Perth.

Since that event, researchers have seen dozens of similar hot spells in ocean regions around the world and have now given them a name — marine heatwaves. Although scientists have come up with a few different ways to define the events, they generally agree that they involve warm spells in surface waters of the ocean that last at least five days and reach a temperature threshold well above the normal range.

The effects of marine heatwaves can reverberate up the food chain, says Pippa Moore, a marine-community ecologist at Newcastle University, UK. Warm, low-nutrient water in the Northwest Pacific during a 2013–16 marine heatwave known as The Blob devastated phytoplankton growth. Then, Chinook salmon (Oncorhynchus tshawytscha) populations plunged, and as many as one million seabirds died in the Gulf of Alaska. Marine heatwaves have also caused massive amounts of coral bleaching in reefs around the world over the past several decades. [Continue reading…]