Remarkable rare images of a Risso’s dolphin appearing to be ‘ridden’ by an octopus providing striking evidence of how an ongoing bloom in octopus numbers may be affecting marine wildlife in the sea off the Devon and Cornwall coast.
The photographs, taken by Risso’s Dolphin Project South West volunteer Bill Coulson off Berry Head, Devon, appear to capture an unusual interaction between a Risso’s dolphin and a common octopus (Octopus vulgaris).
These incredible sightings of a marine animal generally considered a deep-water, offshore species comes as scientists continue to investigate unusually high numbers of octopus which are being recorded around the Southwest coastline.
The abundance of octopus is creating new feeding opportunities for Risso’s dolphins. c. Bill Coulson (Risso’s Dolphin Project South-West project volunteer).
The observation links two major areas of current marine research which are revealing the changes in marine ecosystems as seas warm; the Marine Biological Association’s work examining the increase in abundance of common octopus that began in 2025, and research led by University of Exeter MSc researcher Josh Symes, who is studying Risso’s dolphins across the region using photo ID.
Risso’s dolphins (Grampus griseus) are one of the UK’s least understood cetaceans and are known to feed primarily on squid and other cephalopods. However, the recent abundance of octopus may be creating new feeding opportunities for these distinctive dolphins.
“These photographs offer a fascinating glimpse into the feeding ecology of Risso’s dolphins and the changing marine environment around our coasts. Risso’s dolphins are closely associated with cephalopods, and sightings like this help us understand how they are responding to changing prey availability,” explains Josh. “The images also highlight the value of citizen science, as observations from volunteers are helping us build a clearer picture of marine wildlife across the Southwest.”
The sighting comes amid growing interest in the apparent octopus bloom that has been reported over the last year around the Southwest coast. Although native to UK waters, the species is usually rare, making this the largest bloom recorded in at least 75 years. By surveying fishermen, divers and snorkellers, MBA researchers found that the 2025 octopus bloom was exceptional in both size and geographical spread. Evidence suggests the population likely originated from breeding grounds near the Channel Islands and northern France, with currents carrying young octopus into UK waters. Warmer sea temperatures appear to have played a key role, raising concerns that similar events could become more common as the climate changes.
Dr Bryce Stewart, Senior Research Fellow at the Marine Biological Association, said: “We’re still seeing lots of reports of octopus across Southwest waters, and understanding what’s driving these changes is an important area of research. Observations of interactions between Risso’s dolphins and common octopus help to demonstrate how shifts in the abundance of a species can ripple through the wider ecosystem. It’s a powerful reminder of how interconnected our marine environment is and why we need to continue studying it.”
The findings of species movement are echoed in the South-West Marine Ecosystems State of South-West Seas in 2025 Report, which identifies 2025 as an exceptional year for change in the region’s marine environment. The report describes the common octopus ‘outburst’ as ‘outstanding’, noting that increased octopus abundance has become a significant feature of the southwest marine food web and may be providing new prey opportunities for species – including Risso’s dolphins. It also recorded a continuing upward trend in effort-corrected Risso’s dolphin sightings, likely linked to higher numbers of cephalopods such as cuttlefish and octopus in Southwest coastal waters.
More broadly, the report places these changes within a wider pattern of warming seas, marine heatwave conditions, shifting species distributions and changes to inshore fish, seabed and coastal wildlife communities around the Southwest coast of England.
Recent research led by visiting fellow at the University of Exeter Nicola Hodgins from marine charity Mara, adds further context, showing that Risso’s dolphins around the British Isles form a single genetically distinct population. This matters because changes affecting dolphins in the Southwest may have significance for the wider British Isles population.
Researchers hope that continued monitoring of both octopus populations and Risso’s dolphins will improve understanding of how marine species are responding to environmental change in UK waters and to inform conservation management.
Have you sighted any Risso’s dolphins of the coast of Devon and Cornwall? The MBA and the Risso’s Dolphin Project South West are encouraging members of the public to report sightings of octopus and marine mammals to help support ongoing research. Report sightings via their Facebook page or the iNaturalist app.
iNaturalist sightings provide valuable citizen science records that can help researchers track the distribution and abundance of marine species. Once observations are verified, they can be combined with scientific surveys and other biodiversity datasets, helping organisations such as the MBA and DASSH build a more complete picture of changes occurring in UK marine ecosystems.
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