Marine heatwave likely in UK waters this week

As temperatures over the land breach 30°C, what effect is the prolonged heatwave having on the waters – and marine life – around the UK? Sea-surface temperatures typically lag behind inland weather - what effect are the recent heatwaves having on the marine environment? Image: Adobe. The record-breaking atmospheric heatwave at the end of June, and this week’s intense heat have elevated sea-surface temperatures, which could spell bad news for marine life. Surface waters in the Northwest European seas are an average of 2°C warmer than usual – typically those experienced in August – with many areas experiencing moderate to severe marine heatwave conditions. Warmer sea surface temperatures The Met Office warned that much of the English and Welsh coastlines, including the English Channel, experienced category 2 marine heatwave conditions last week. Sea-surface temperatures were about 1.5-4°C above normal, with temperatures between 15 and 19°C. Prolonged periods of heat can trigger mass die-offs of some seagrasses, shellfish and other species, and can encourage greater numbers of warm-water creatures including octopus. Related article UK weather: Amber alerts as 36°C heatwave grips Britain – how long will it last? In the Irish Sea, English Channel and southern North Sea – areas which are tidally-mixed – higher temperatures also affect the deeper waters of the sea and anomalies of around +2°C have been observed below the surface. The English Channel, which has already experienced marine heatwave conditions for much of this year, is particularly susceptible to further warming. Dr Ségolène Berthou, Air-Sea Interaction Specialist at the Met Office, said: “Marine heatwaves around the UK have developed rapidly following the recent heat dome, and we are now seeing widespread strong to locally severe conditions. This is the third and most intense marine heatwave we have seen this year.” This week, as inland temperatures have breached 30°C in many parts of the country, the sea surface will have a limited chance to cool. “While these warmer seas did not significantly increase peak temperatures on land, they reduced night-time cooling and helped sustain warmth, particularly in coastal areas,” added Berthou. “With further sunny and calm weather likely next week, there will be little opportunity for the ocean to release this excess heat. This means the surface marine heatwave could intensify further, potentially reaching extreme levels in the south. Such conditions would be highly unusual for UK waters.” Sea-surface temperatures typically lag behind inland weather by between three and five days so it’s likely the current marine heatwave will intensify, with the potential for a rarely-recorded Category 4 extreme marine heatwave. Bad news for marine life Marine heatwaves can have significant impacts on ecosystems and wildlife, causing shifts in fish populations, damage to important habitats like seagrass and kelp, and increasing the likelihood of harmful algae blooms. Marine heatwaves can cause damage to damage to important habitats like seagrass and kelp. Image: Adobe. “These changes can result in mass-mortality events for some marine species and alter the distribution of commercially-important fish and shellfish,” said Prof. John K. Pinnegar is the Principal Scientist and Lead Advisor (Climate Change) at Centre for Environment, Fisheries and Aquaculture Science (CEFAS). “Prolonged periods of elevated seawater temperatures can also encourage new species to visit UK waters, establish new populations, potentially shaking up UK ecosystems. A recent example includes the population bloom of common octopus we've been experiencing since last year, with serious negative consequences for crab and lobster fisheries in southwest England.”