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’s coast. This year, the bloom is the largest it’s been in 75 years.

Normally, octopus larvae that drift into cold waters die. But this year’s 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.

The change in species has been a boon for local fishers selling octopus into the lucrative European export market. (Octopus landings along the U.K.’s 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.

“It has completely shaken up the food chain,” said Bryce Stewart, a senior research fellow at the UK’s 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’t dying. They’re reproducing.

And the marine heat wave continues.

An estimated 82 percent of the world’s oceans are currently experiencing marine heat waves.

Globally, marine heat waves — prolonged periods of unusually warm water — are becoming more common, more intense, longer lasting, and more widespread, experts say. This year, ocean heat is unusually severe, setting new temperature records. According to Global Climate Risks, a nonprofit created by scientists to publicize the effects of climate change, an estimated 82 percent of the world’s oceans are currently experiencing marine heat waves. Evidence from recent hot spells suggests the impacts on sea life could be profound and long-lasting.

Read the full article about marine heat waves by Jim Robbins at Yale Environment 360.