Photo by Stephanie Harlacher
A dramatic population bloom of the common octopus (Octopus vulgaris) off the Southwest coast of the UK is having significant effects on fisheries and marine ecosystems, according to a new report led by the Marine Biological Association in collaboration with Plymouth Marine Laboratory, the University of Plymouth and an independent consultant. The study, funded by Defra, Plymouth City Council and Devon County Council, draws on data from scientists, fishermen and citizen scientists.
The common octopus is native to UK waters but typically rare, favouring warmer seas in southern Europe and the Mediterranean. Only four major population blooms have been recorded in the past 125 years: in 1899-1900, 1932-33, 1950-51, and now since 2025. The current bloom, which accelerated from January 2025, appears to be at least as extensive as any previously recorded and is still continuing.
Lead author Dr Bryce Stewart, Senior Research Fellow at the MBA and Associate Professor at the University of Plymouth, said “This is an extraordinary event that tells us a lot about how marine life is responding to a warming ocean, and the survey reveals the mixed effect that this has had on fisheries.”
Climate link and cross-Channel connections
The research team found that unusually warm sea temperatures during bloom years and the preceding year were a consistent factor in all recorded blooms. Sustained easterly winds may have helped transport young octopus larvae from the Channel Islands and northern France. Ocean current modelling supports this, showing that larvae from Guernsey, which has experienced its own octopus bloom since 2024, likely contributed to the UK surge.
A survey of 40 fishermen revealed mixed impacts from the octopus surge. While some adapted to catching octopus and benefited economically for a period, over half reported negative impacts, particularly those targeting brown crabs, lobsters and scallops, which suffered heavy predation from the octopus. Catch rates for those species dropped by 30% to 50% in 2025, raising concerns about long-term damage to shellfish stocks.
Councillor Julian Brazil, Leader of Devon County Council, said “These findings are a concern, and it justifies the urgency in carrying out this vital research at the earliest opportunity. The study has highlighted that the influx of octopus on our waters is an issue which is likely to be increasingly frequent.”
Breeding breakthrough and ecosystem concerns
Multiple reports of octopus breeding and sightings of juveniles in UK waters in 2025, previously almost unheard of, suggest the current bloom may continue or reoccur soon. Researchers warn that the sudden influx of this adaptable predator could disrupt food webs, with unknown consequences for biodiversity and resilience.
Professor Tim Smyth, Director of Science at Plymouth Marine Laboratory, stated “Thanks to Plymouth’s unique wealth of long-term marine records, stretching back more than a hundred years, and the extensive references held in the National Marine Biological Library at the Marine Biological Association documenting historic octopus blooms, we were able to forensically investigate the causes behind last summer’s outbreak. What we are seeing is clear: shifts in the marine climate are reshaping our ecosystems.”
The report calls for continued monitoring through MBA trawl surveys, University of Plymouth BRUV (Baited Remote Underwater Videos) work, and enhanced Cefas stock assessments. It recommends the proposed OctoPulse model of ocean conditions developed at Plymouth Marine Laboratory, early detection of octopus larvae in plankton, and easier reporting systems for fishermen via apps or digital platforms.
Councillor Tudor Evans, Leader of Plymouth City Council, emphasised “We need to move beyond reactive measures and there needs to be serious investment in predictive tools and support to help fishers to adapt and safeguard a fishing fleet for the future. This is not a one-season issue. It’s a long-term challenge that demands a long-term fix.”
Professor Emma Sheehan, Professor of Marine Ecology at the University of Plymouth, added “It is essential that we monitor any changes in abundance, distribution and movement, and that we assess octopus relationships with other species such as useful associates, prey or predators.”
Dr Stewart concluded “If these conditions persist, octopus blooms could become a more regular feature of our changing seas. Understanding their causes and consequences is vital to help both ecosystems and coastal communities adapt.”