Marine heatwaves affect people too

Climate change has made extreme weather events increasingly common around the world – and marine heatwaves are no exception. We know these periods of unusually high seawater temperatures generally have negative ecological impacts – but what about other implications and flow-on effects?

A paper published this week in Science provides the first global perspective of the socioeconomic impacts of marine heatwaves.

The study, led by scientists from the Marine Biological Association (MBA) in the UK and involving Associate Professor Alex Sen Gupta from UNSW’s Climate Change Research Centre, showed that ecological impacts of marine heatwaves often led to major economic losses and wider effects on society across the world.

“The global annual number of marine heatwave days has risen by 54 per cent over the past century, with eight of the 10 most extreme marine heatwaves ever recorded occurring after 2010,” A/Prof. Sen Gupta said.

“We already know a lot about the drivers and biological impacts of those heatwaves, but only a few studies have looked at their consequences for human-ocean interactions.”

To help close that evidence gap, the research team examined biological responses to 34 marine heatwaves occurring across all major ocean basins and explored the related socioeconomic impacts. They found that most events resulted in loss of fisheries, destruction of kelp forests or seagrass habitats, or mass mortalities of wildlife, often causing significant economic loss to multiple industries.

“We found that economic losses of single marine heatwave events to date exceed US$800 million in direct losses and additional, substantial indirect losses,” said lead author, Dr Katie Smith from MBA .

“The true costs are likely to be even greater because many socioeconomic effects remain unknown and underreported, particularly in lower-income countries.”

For example, the Ningaloo Niño marine heatwave that hit the coast of Western Australia in 2011 led to massive and sustained loss of kelp habitat, fisheries closures and the invasion of tropical species into temperate waters.

Dr Smith said the impacts of marine heatwaves were far-reaching. “The knock-on effects can last for decades,” she said.

“The loss of coastal habitats such as seagrass meadows and kelp forests impacts fisheries, tourism, and natural capacity to store carbon.

“During marine heatwaves ocean temperatures can become so high that some species become stressed or even die, which in turn can affect foodwebs and impact higher predators. For example, a change in microscopic marine animals can ricochet up the foodweb, causing mass mortalities in important fisheries species, endangering sea lions and seabirds and leading to huge financial loss to fisheries and tourism.”