![\"Sunset](\"https:\/\/www.newsbeep.com\/ca\/wp-content\/uploads\/2026\/09\/GettyImages-2246914484.jpg\")
<\/p>\n\t<\/p>\n
James David Phenicie\/Getty Images<\/p>\n
\t\t\t\tGet your news from a source that\u2019s not owned and controlled by oligarchs. Sign up for the free Mother Jones Daily.<\/a><\/p>\n This story was originally published by\u00a0Yale Environment 360<\/a>\u00a0and\u00a0is reproduced here as part of the\u00a0Climate Desk<\/a>\u00a0collaboration.<\/p>\n The common octopus is a warm water species that usually lives in the temperate waters of the Mediterranean. But last year, octopus larvae hitchhiked across the English Channel attached to plankton, resulting in an octopus bloom off England\u2019s coast. This year, the bloom is the largest it\u2019s been in 75 years.<\/p>\n Normally, octopus larvae that drift into cold waters die. But this year\u2019s bloom, experts say, is the result of an unusually intense marine heat wave off of Devon and Cornwall, which raised water temperatures up to 9 degrees F above normal.<\/p>\n The change in species has been a boon for local fishers selling octopus into the lucrative European export market. (Octopus landings along the UK\u2019s southwest coast were roughly 7,700 percent higher than usual in 2025.) And while the invasion has slashed the catch of scallops, lobster, and crab, it has boosted numbers of seals, conger eels, and dolphins, which eat octopus. The warming, in combination with abundant prey, has also drawn bluefin tuna and sharks to British waters for the first time in decades.\u00a0<\/p>\n An estimated 82 percent of the world\u2019s oceans are currently experiencing marine heat waves.<\/p>\n \u201cIt has completely shaken up the food chain,\u201d said Bryce Stewart, a senior research fellow at the UK\u2019s Marine Biological Association, which has been studying the phenomenon. While this kind of bloom has happened here before, he said, this one is different. During past surges, the return of cold water killed off the octopuses. This time, the octopuses aren\u2019t dying. They\u2019re reproducing.\u00a0<\/p>\n And the heat wave continues.<\/p>\n Globally, marine heat waves\u2014prolonged periods of unusually warm water\u2014are becoming more common, more intense, longer lasting, and more widespread,\u00a0experts say<\/a>. This year, ocean heat is unusually severe, setting new\u00a0temperature records<\/a>. According to Global Climate Risks, a nonprofit created by scientists to publicize the effects of climate change, an estimated\u00a082 percent<\/a>\u00a0of the world\u2019s oceans are currently experiencing marine heat waves. Evidence from recent hot spells suggests the impacts on sea life could be profound and long-lasting.\u00a0<\/p>\n Ocean fevers can rearrange marine ecosystems, drive fish to move into deeper, colder layers of the sea, trigger coral bleaching, and cause widespread marine die-offs. They can increase the severity and number of algal blooms, which harm fish, shellfish, marine mammals, and birds. And they can cause extreme weather events, like tropical storms and hurricanes, and upend fishing and tourism.\u00a0<\/p>\n To officially be called a heat wave, temperatures must rise above the 90th percentile of normal seasonal variation for five consecutive days. While marine heat waves do occur naturally, climate scientists say anthropogenic warming has\u00a0exacerbated<\/a>\u00a0them. According to NOAA scientists, oceans have absorbed more than\u00a090 percent<\/a>\u00a0of the excess heat produced by human-caused global warming. One recent\u00a0study<\/a>\u00a0found that, since 1940, warming has led to a threefold increase in the number of days per year with extreme heat at the ocean surface.<\/p>\n Climate warming and marine heat waves are separate phenomena with different effects. Ocean warming is gradual and allows more time for species to adapt and evolve. Marine heat waves are acute and produce rapid and extreme changes that give organisms little time to adapt. But the long-term warming trend is making ocean heat more severe.<\/p>\n Climate change has raised the temperature of the waters off the UK by around 2 degrees F above average in the last six decades, worsening this year\u2019s record heat. Records have fallen elsewhere in Europe as well. \u201cWe find it\u2019s the most extreme July marine heat wave conditions for the Western Mediterranean, the Celtic Region, and for the Bay of Biscay and Iberian Peninsula,\u201d said Catherine Gregory, a climate scientist at the University of Bern.<\/p>\n The Pacific has warmed in northern regions by almost 2 degrees F and is currently experiencing the world\u2019s largest marine heat wave, which sprawls over more than 24 million square miles. And in the central and eastern Pacific, things are bound to get worse.\u00a0<\/p>\n Seabirds in South America have been dying in large numbers, a trend experts say is linked to higher ocean temperatures.<\/p>\n This year\u2019s El Ni\u00f1o is expected to be the strongest in living memory\u2014it has already spiked sea temperatures far earlier in the year than expected\u2014and scientists fear it will expand the size and intensity of the two existing marine heat waves off the California coast. Based on studies of past heat waves\u2014in particular, an event known as the Blob, the largest marine heat wave on global record, which dramatically raised temperatures in the eastern Pacific between 2014 and 2016\u2014scientists are warily watching the warming ocean, anticipating a cascade of severe impacts both onshore and off.\u00a0<\/p>\n The Blob began to form in the fall of 2013, when a persistent high-pressure ridge greatly reduced the cool winter winds that normally blow over the eastern Pacific. Without that cooling, the sun created a very large body of very warm water. In 2014, ocean temperatures were 7 degrees F above average, and the cold, nutrient-rich water that normally coursed along the West Coast disappeared.\u00a0<\/p>\n The ecological changes were legion. In 2015, researcher Ric Brodeur was monitoring populations of shrimp-like krill, which form the base of the marine food chain, expecting his sampling nets to be full. Instead, they were almost empty. \u201cYou could fit all the krill from the trip into a little plastic bag,\u201d he said.\u00a0<\/p>\n The lack of food caused humpback whale numbers in the North Pacific to\u00a0drop<\/a>\u00a0by an estimated 7,000\u2014or 20 percent of the population. Many females became emaciated, which reduced calf survival and caused a reproductive decline that didn\u2019t\u00a0begin to reverse<\/a>\u00a0until 2021, five years after the Blob had officially ended.\u00a0 \u00a0<\/p>\n While many anomalies caused by the unusually warm water were temporary, some were not. The Blob\u2014which at times approached 10 degrees F higher than average\u2014caused large-scale and long-term ecosystem changes, some of which persist to this day. Researchers are concerned that today\u2019s warming waters will compound the damage caused by previous marine heat waves.\u00a0<\/p>\n One of the most egregious of those earlier changes was the die-off of kelp forests along thousands of miles of coast, from Baja California to as far north as British Columbia. Kelp complexes are some of the most dynamic and biologically productive ecosystems on Earth, the \u201cunderwater rainforests\u201d of temperate and Arctic coastal oceans. They offer food, nursery grounds, and shelter from predators and rough currents to hundreds of marine species. Kelp canopies, which consist of rubbery floating fronds, are home to sea otters, seabirds, and juvenile fish, while abalone, sea urchins, lobsters, and octopus live on or near the seafloor.\u00a0<\/p>\n \u201cThe Pacific kelp forest has lasted for millions of years,\u201d said Melissa Carter, a biological oceanographer with UC San Diego\u2019s Scripps Institution of Oceanography, thanks to upwellings of cold water along the coast. \u201cBut it has a specific temperature threshold where it falls apart and it can\u2019t survive. And everything that lives on the coast depends on that ecosystem.\u201d<\/p>\n One of the largest algal blooms in history now stretches from Southern California to the coast of British Columbia.<\/p>\n One\u00a0study<\/a>\u00a0found that during the Blob, overall kelp cover dropped considerably: Northern California was hardest hit, with 95 percent of its kelp wiped out. The loss of kelp reshaped the entire food web, decimating red abalone populations, which were already in trouble, and prompting the state of California to extend its ban on recreational fishing of the species at least until April 2036.<\/p>\n The Blob also severely impacted seabirds. Half of Alaska\u2019s common murres\u2014some 4 million birds\u2014starved to death as warmer currents disrupted migrations of anchovies, sardines, and other forage fish. \u201cRecent population abundance estimates since then have found no evidence of recovery,\u201d the authors of a\u00a02024 study<\/a>\u00a0of the murres concluded, \u201csuggesting that the heatwave may have led to an ecosystem shift.\u201d \u00a0<\/p>\n Current marine heat waves are already taking a toll. Dead and dying birds, including California brown pelicans, loons, and grebes, are turning up again on Southern California beaches. \u201cWe\u2019re seeing cormorants walk to shore and then just die within the hour,\u201d Tammy Russell, a researcher at the Scripps Institution of Oceanography, told the Associated Press, \u201cand we\u2019re seeing it happening across the whole coast.\u201d Seabirds along South America\u2019s Pacific coast have been\u00a0dying<\/a>\u00a0in large numbers in recent months, and experts have linked the fatalities to higher ocean temperatures.<\/p>\n Researchers are\u00a0concerned<\/a>\u00a0that current record-setting ocean temperatures, intensified by the strengthening El Ni\u00f1o, will further harm corals. Bleaching occurs when rising water temperatures, in addition to other stressors like pollution and overexposure to sunlight, spur corals to release their symbiotic algae, which harvest energy for them. A bleaching event that lasted from early 2023 until mid-2025 affected more than 84 percent of the world\u2019s coral reef areas.\u00a0In a major\u00a0report<\/a>\u00a0that was just released, Global Coral Reef Monitoring Network researchers warn that coral reefs around the world are seeing a rapid increase in bleaching and that recovery windows between disturbance events are narrowing.\u00a0<\/p>\n Marine heat waves can affect conditions throughout the water column. When a cap of warm water forms at the ocean\u2019s surface, it prevents vertical mixing and can promote the growth of harmful algal species. The explosion of aquatic organisms depletes oxygen in the water, blocks sunlight, and can release harmful toxins into the air and water.\u00a0<\/p>\n