Are heat waves harmful to our oceans?

In a world increasingly shaken by the ongoing climate crisis, it is perhaps unsurprising that our oceans are feeling the effects of climate change. Long-term effects of marine heatwaves.

Right on our doorstep is the Mediterranean area is a special hotspot for this phenomenon.

In some parts of the sea, temperatures can be 5, 6 or even 7 degrees above average.

That’s not good news for marine ecosystems, as habitats disappear and fish stocks move to other parts of the ocean.

Pippa Moore is a professor of marine sciences at University of Newcastle in the UK. She hopes changes can be made to mitigate the worst effects of marine heatwaves.

Moore was working as a postdoctoral researcher in Western Australia in 2011 when a major heat wave at sea affect the region.

The incident caused significant environmental disruption, including the closure of kelp forests and widespread loss of scallops, and caused major disruptions to many fisheries.

She was devastated, but also determined.

“In 2014, I joined a working group on marine heat waves, where we defined marine heat waves by stealing them from atmospheric scientists and then continued to research them,” she says.

What is meant by a maritime heat wave?

Over the past decade, she and her fellow experts have tracked the peaks of abnormally hot waterthat are changing underwater ecosystems with a force that resonates far beyond the surface.

Nowadays, the definition of these underwater heat waves is quite clear and different from heat waves on land.

“It takes longer for water to warm up and cool down, so we felt three days was too short,” Moore explained. Ultimately, “they defined a marine heat wave as values ​​above the 90th percentile for five days or more.”

Samantha Burgessthe deputy director of the EU Copernicus Climate Change Servicealso began her work on marine heat waves while studying for her PhD in Australia, but she approached the topic in a different way.

She discovered the existence of the heat waves in relation to previous coral bleaching events, particularly those associated with El Niño.

“We all know now that El Niño events lead 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,” Burgess says. “You know, tracking these signals through the coral skeletons really shows how our ocean has changed dramatically in recent times compared to the hundreds and thousands of years of archive that we have before that.”

Many people are already aware of marine heat waves through mainstream climate news, but they also impact fragile underwater ecosystems, potentially having a cascade of consequences.

While a recreational swimmer may enjoy warmer sea temperatures, these thermal anomalies disrupt the fragile balance of marine life.

In 2016 in Californiathere was a particularly severe heat wave – now known as “the blob”.

The plankton communities were directly affected and because they provide food for organisms higher up in the food chain, the consequences were disastrous.

“There was a huge mortality of seals and birds, not just because of the direct effects of temperature changes on those birds or marine mammals, but also because of changes in their diet, where their food didn’t arrive at the same time as their breeding food,” Burgess explains.

The event highlighted how interconnected marine ecosystems are and how important it is to learn more about heat waves and how we can prevent them.

Is there any hope of limiting the damage caused by marine heat waves?

As always in the oceans, the effects of any given stress on the ecosystem result in a nuanced tapestry of winners and losers.

Burgess explains that some marine organisms have already managed to evolve adaptation strategies of their own.

“Research plays a really important role in understanding refuges,” she says. “Some specific species in some locations seem to be better adapted to extreme temperatures.”

For scientists, it’s critical to “understand why that ecosystem in that complex environment seems to thrive at slightly warmer temperatures,” she says.

Overall, the The impact of heat waves at sea extends far and widewhich also casts a shadow on man and his livelihood.

“A heatwave at sea could potentially lead to harmful algal blooms or increases in viruses such as Vibrio,” Moore says. For fish stocks, that could disastrous.

A few years ago, millions of euros worth of fish were lost in Chile due to algal blooms.

After years of research, scientists have a better idea of ​​how to predict when ocean temperatures will rise dangerously high.

“We can make these predictions so we can actually minimize the impact,” Moore explains.

“Colleagues in Tasmania have developed forecasting tools for maritime heatwaves that they are reasonably confident they can predict up to six months in advance,” says Moore.

This allows fisheries managers and other authorities to close vulnerable areas and give nature a chance to fend for itself, without being affected by human activities.

Despite this positive step, there is still much work to be done and the road ahead is shrouded in uncertainty.

Research is critical. It is essential to unravel the mysteries of resilient ecosystems and to determine the most effective climate reserves.

It is particularly urgent because the global ocean surface is currently above 21 degrees – and has been for almost a year – and Coral bleaching is so common.

Current Average ocean temperatures are unprecedentedand the long-term effects of these persistent temperatures, as well as the spikes in water temperature during heat waves, are not well modelled or understood.

To learn more about the worrying phenomenon of maritime heatwaves, listen to the full episode of Ocean Calls in the player above.

Many thanks to our guests, Samantha Burgess, Deputy Director of the European Copernicus Climate Change Service and Pippa Moore, Professor of Marine Science at the University of Newcastle in the UK.

At the end of the episode we hear from Chloë McCardel, an Australian swimmer who has been nicknamed the ‘Queen of the Channel’. She has crossed the Channel 44 times and has encountered a lot of jellyfish along the way.

Ocean Calls is produced in collaboration with the European Commission’s Directorate-General for Maritime Affairs and Fisheries.

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