Britain faces an alarming future of increasingly severe marine heatwaves, which threaten to devastate shellfish colonies, fisheries, and coastal communities across the UK.

A report from the National Oceanography Centre (NOC) in Southampton highlights the urgent need for targeted research into how these sudden seawater temperature surges could impact marine habitats and seafood production.

Globally, marine heatwaves are becoming more frequent and intense due to rising fossil fuel emissions, which drive up atmospheric and ocean temperatures. These heatwaves disrupt marine ecosystems, causing coral bleaching, harmful algal blooms, seagrass destruction, and mass die-offs of fish, seabirds, and marine mammals.

“Marine heatwaves have catastrophic impacts and we need to be prepared for them. At present, we are not and that position needs to be rectified as a matter of urgency,” said Dr Zoe Jacobs, the lead author of the NOC report, Marine heatwaves and cold spells in the Northeast Atlantic: what should the UK be prepared for?

“We need to know how these marine heatwaves are going to affect plants and animals that live in the sea and find ways to protect them, as well as the coastal communities that depend on them.”

In early summer 2023, Britain experienced a significant marine heatwave, with seawater temperatures off northeast England and west Ireland rising about 5°C above normal for over two weeks. This shattered records for late spring and early summer.

Simultaneously, the Met Office reported record-high sea temperatures in the North Sea and North Atlantic, marking unprecedented levels since records began in 1850.

As global temperatures continue to rise, scientists predict more record-breaking marine heatwaves will affect waters around Britain and Ireland.

The NOC report identifies three particularly vulnerable areas: the Irish Sea between England and Ireland, the North Sea off northern England and Scotland, and the southeast coast of England.

“These regions are areas where marine heatwaves can coincide with extremely low oxygen concentrations in the water, which makes them especially vulnerable. It’s like a double whammy. They get the extreme heat stress and extremely low oxygen levels at the same time. And that is going to cause serious trouble for any creatures or plants that are living there,” said Jacobs.

The long-term effects of these temperature spikes remain uncertain, posing challenges for researchers and conservationists.

The problem for researchers and marine conservationists is that the long-term consequences of such jumps in temperature are still unknown. “There have been stories that there were widespread die-offs of shellfish such as whelks, and disruption to many fisheries during last year’s heatwave, but there is no hard evidence to back up these because we have not carried out any detailed research into the exact effects, and that is a problem.

“Global temperatures are rising and we are going to experience more and more marine heatwaves as a result. These are already having catastrophic impacts in other parts of the world, for instance in waters off Australia and other regions where fisheries have had to be closed and hectares of seagrass have been wiped out. We need to be able to pinpoint our most vulnerable regions and monitor them very closely.”

Seagrass meadows, for example, are critical ecosystems around the UK’s shores. These habitats absorb significant amounts of carbon and provide shelter for diverse marine species. However, they have been severely depleted in the past, and restoration efforts are ongoing. The potential impact of marine heatwaves on these fragile ecosystems is a pressing concern.

“However, we do not know what will happen to that programme if marine heatwaves start to kill off seagrass again,” added Jacobs. “We need to understand how this will happen and investigate now to find out if there are strains that are more resilient than others and concentrate on planting these.

“At the same time, we may need to be prepared to close down fisheries at certain times or impose quotas to protect them as heatwaves start to strike. These are the kinds of actions that have had to be imposed in other parts of the world and we may have to follow suit.”