Around the world, such instances of unusually warm sea temperatures for five days or more have caused die-back of key species such as kelp<\/a>, seagrass<\/a> and corals<\/a>.<\/p>\n Marine heatwaves have also caused death or changes to the life cycles<\/a> of marine mammals and shellfish, as well as other species that depend on them, such as seabirds. They have caused species to migrate or shift their geographic range<\/a>. These changes all disrupt ecosystems, with disastrous ramifications for oceanic food webs<\/a>.<\/p>\n The UK\u2019s first major marine heatwave, in June 2023<\/a>, has been followed by another in May 2025<\/a> and the current heatwave in July 2026<\/a>. Evidence of the impacts of these marine heatwaves is still quite limited, because some consequences can be subtle or take years to detect.<\/p>\n Extreme heat has been linked to harmful algal blooms<\/a> around the UK. A surge in growth of microscopic algae develops when nutrients, warm temperatures, abundant sunlight and calm water combine to create ideal growing conditions.<\/p>\n Algal blooms can produce harmful toxins that accumulate in filter-feeding shellfish, causing severe illness or death in people who eat them. For that reason, the UK government works with food safety authorities to actively monitor marine biotoxins<\/a>.<\/p>\n Warmer waters may have caused the influxes of octopus<\/a> to the south coasts of Devon and Cornwall. Their predation on crab and lobster from pots has altered local fishery dynamics, with some fisheries now focusing on catching octopus<\/a>.<\/p>\n A surge in jellyfish sightings has been suggested as another possible consequence of the latest marine heatwave. But early evidence suggests this may be due to more people at the beach<\/a> reporting their observations.<\/p>\n Seabirds such as razorbills rely on fish as a food source \u2013 but marine heatwaves can destabilise the ocean\u2019s food web. Anecdotally, fishers have reported cold-water species such as cod shifting northward<\/a>. Aside from affecting catch, such shifts may also affect seabird breeding and survival.<\/p>\n Seagrass beds and kelp forests have their own microclimates which can provide sanctuary from extreme heat<\/a>. But they are also under threat from marine heatwaves, as warmer waters hinder their ability to provide refuge for marine species.<\/p>\n Because of changes to fisheries and ocean health, marine heatwaves have huge social and economic consequences<\/a>.<\/p>\n In Western Australia<\/a>, the consistently warm seas led to the coining of the term \u201cmarine heatwave\u201d in 2011. This caused decimation of seagrass meadows<\/a>, along with die-back of kelp, corals, fish, abalone, prawns and crabs<\/a>. Some parts of that marine ecosystem took years to recover; other parts have never bounced back<\/a>. <\/p>\n Forty questions<\/p>\n Now, the race is on to understand the knock-on effects of marine heatwaves and which marine species are most threatened.<\/p>\n Management interventions, such as harvest strategies or catch quotas, can protect breeding populations and young fish<\/a>, helping to maintain healthy fish and shellfish numbers. The earlier these interventions are implemented, the better.<\/p>\n Marine heatwaves can affect fish survival.![\"black](\"https:\/\/www.newsbeep.com\/ie\/wp-content\/uploads\/2026\/07\/file-20260716-57-2qnubq.jpg\")
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