Are marine heat waves killing our oceans?

In a world increasingly upset by the ongoing climate crisis, it is perhaps unsurprising that our oceans are feeling the long-term effects of marine heat waves. The Mediterranean is a particularly hot spot for this phenomenon. In some areas of the sea, temperature anomalies of 5, 6 or even 7 degrees above average can be observed, it says euronews.com. This is not good news for marine ecosystems as habitats disappear and fish stocks move to different areas of the ocean.

What are sea heat waves?

For the past decade, scientists have been studying the tides of unusually warm water that reshape underwater ecosystems with a force that resonates far beyond the surface. The definition of these underwater heat waves is quite clear and different from land-based heat waves.

“It takes longer for the water to warm up and cool down, so we thought three days was too short. We ended up defining a marine heatwave as values ​​above the 90th percentile for five days or more," says Pippa Moore, professor of marine sciences at Newcastle University in the UK.

She hopes changes can be made to mitigate the worst effects of marine heatwaves.

Samantha Burgess, deputy director of the EU's Copernicus Climate Change Office, also began her work on marine heatwaves while studying for a PhD in Australia, but approached the issue in a different way.

"We all know now that El Niño leads to high sea surface temperatures, particularly around the Great Barrier Reef and the east coast of Australia - but increasingly in other parts of the world," says Burgess. "You know, tracking these signals through the coral skeletons really shows how our ocean has changed dramatically recently compared to the record of hundreds and thousands of years that we have before that," she adds.

While the occasional swimmer may enjoy warmer sea temperatures, these thermal anomalies disrupt the delicate balance of marine life. In 2016, there was a particularly severe heat wave in California – now called the “spot”. Plankton communities were directly affected, and since they are food for organisms higher up the food chain, the impact was catastrophic.

"There was a lot of mortality in seals and birds, not only because of the direct effects of temperature changes on those birds or marine mammals, but also because of changes in their food, which meant that their food wasn't arriving at the same time that they were ready for their breeding,” explains Burgess.

This event clearly revealed the interconnectedness of marine ecosystems and the importance of learning more about these heat waves and how to prevent them.

Can the damage caused by marine heat waves be reduced?

Burgess explains that some marine organisms have already been able to develop adaptive strategies for themselves.

"Certain species in some places seem better adapted to temperature extremes. For scientists to be able to understand why, in this complex environment, this ecosystem seems to thrive at slightly higher temperatures is crucial," she says.

Overall, however, the effects of marine heatwaves are far-reaching, casting a shadow on people and their livelihoods as well.

"A marine heat wave could potentially lead to harmful algal blooms or an increase in viruses such as Vibrio. For fish stocks, it could be catastrophic," says Moore.

A few years ago, millions of euros worth of fish were lost in Chile due to algae blooms. After years of research, scientists have built a better picture of how to predict when ocean temperatures will rise dangerously high.

"Colleagues in Tasmania have developed marine heatwave forecasting tools that they feel quite confident in predicting up to six months in advance. This allows fisheries management and other authorities to close sensitive areas and give nature a chance to save itself, without the pressures associated with human activity," says Moore.

Research is critical, and the need to unravel the mysteries of resilient ecosystems and understand the most effective climate refuges is an urgent matter. This is especially pressing given that the global ocean surface is currently above 21 degrees – and has been for nearly a year – and coral bleaching is so widespread.

Current average ocean temperatures are unprecedented, and the long-term effects of these sustained peaks, as well as spikes in water temperature during heat waves, are not well modeled or understood.