Marine Heatwave Threatens UK Coastal Ecosystems
The Met Office has forecasted that parts of the UK could experience an "extreme" marine heatwave later this week, raising significant concerns for marine ecosystems and local fishing communities.
Prolonged elevated sea temperatures can cause mass mortality events among seagrasses, shellfish, and other marine species, while simultaneously promoting the proliferation of warm-water species such as octopus.
The current heatwave is most intense off the eastern and southern coasts of England, with sea temperatures expected to be 4-5°C above average in some areas.
This marine heatwave has been intensified by the "heat domes" responsible for record-breaking air temperatures in May and June, compounded by the ongoing long-term warming of oceans attributed to climate change.
Marine habitats like seagrasses and kelp forests, which thrive in cooler waters, are vulnerable to heat stress during such temperature surges. This stress can inhibit their growth or cause widespread die-offs, potentially disrupting the species that depend on these habitats.
Historical Context and Scientific Concerns
The UK has previously experienced marine heatwaves, defined as extended periods of unusually high sea surface temperatures. However, scientists are concerned that this event could be particularly severe and prolonged, especially in the English Channel and the southern North Sea.
"We're starting to see temperatures now that we would expect to see at the height of summer, [at the] end of August," said Dr Zoe Jacobs of the National Oceanography Centre in Southampton.
"So, if this event keeps coming… we might start seeing some serious impacts on ecological systems."
Researchers have also observed longer-term shifts in the UK's marine biodiversity. Species adapted to cooler waters, such as cod, are generally moving further north, while populations of warm-water species like octopus have increased around south-west England.
While natural cycles and fishing practices influence species abundance, many scientists emphasize the critical role of rising sea temperatures.
Impact on Fisheries and Marine Species
Fishermen in some UK regions have adapted by targeting octopus due to their increasing numbers.
"It can be exciting to see new species arrive and we all enjoy seeing something like an Atlantic bluefin [tuna] or an octopus, but the problem is we've also got the negative impacts of that," said Prof Matt Frost of the Plymouth Marine Laboratory.
"We're seeing a decline in the numbers of cod and other key species… you're also getting other species that could displace native species. That could bring disease [and] all sorts of problems."
Although the rise in octopus populations may provide new economic opportunities for fishermen, these predators can adversely affect populations of crabs, lobsters, scallops, and other shellfish.
Increasing Intensity of Marine Heatwaves
The southern North Sea and English Channel are relatively shallow, enabling rapid warming when air temperatures rise. In late May and late June this year, persistent high-pressure systems over Europe caused air temperatures to increase, which subsequently transferred heat to the surrounding seas.
Despite their rarity in the past, extreme marine heatwaves are becoming more frequent and intense due to the baseline warming of oceans.
Since the 1980s, the UK's seas have warmed steadily, primarily driven by human-induced climate change.
"We are likely to see marine heatwave conditions becoming average towards the middle-to-end of the century," warned Dr Ségolène Berthou, air-sea interaction specialist at the UK Met Office.
"So, this is projected to increase if we don't cut greenhouse gas emissions."
Additional Information and Resources
Additional reporting by Tom Ingham.
include record warm seas facilitating the arrival of extraordinary new species in UK waters, the declaration of a 'Year of Octopus' following record numbers, and accessible guides to climate change impacts.
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