Tens of thousands of fish have died off northwestern Australia, as a large and long-lasting marine heat wave intensifies.
The fish kill at Gnoorea Beach near Karratha is concerning our team of scientists, as the hot mass of water heads south towards Ningaloo Reef and the seagrass gardens in Shark Bay. That’s because we’ve seen this before. An enormous marine heat wave in 2010–11 devastated fisheries and ecosystems further down the WA coast.
This marine heat wave began in September, with temperatures up to 3°C warmer than usual off Broome. There’s no end in sight.
The heat wave comes as oceans worldwide experience recordbreaking heat, driven by climate change. More than 90% of all heat trapped by greenhouse gases goes into the oceans.
The fish kill is a visible way to glimpse a disaster often out of sight and out of mind. But these marine heat waves do much more, from wiping out seagrass meadows and kelp beds to trashing fisheries.
The current marine heat wave is, so far, the second-worst in Western Australia’s recorded history.
Over the 2010–11 summer, a severe marine heat wave devastated seas off the state. Temperatures hit up to 5°C above average, peaking in February and March.
The heat led to local extinction of kelp species along a 100km stretch of coastline. Scallop and blue swimmer crab fisheries had to close. Seagrass meadows in Shark Bay collapsed. Tropical species were sighted in new areas. And coral bleached at Ningaloo.
As the climate changes, modeling indicates marine heat waves will hit more often and to intensify.
Worldwide, marine heat waves have devastated ecosystems. One of the worst, the Pacific “blob” heat wave of 2014–2016, killed an estimated 100 million Pacific cod and four million birds from a single seabird species, as well as contributing to the starvation of about 7,000 humpback whales. The intense heat killed off cold-loving species and paved the way for tropical species to enter and even thrive.
Right now, 28% of the world’s oceans are in heat wave conditions, based on surface temperatures.