The death of crabs on the coast of the UK may be caused by an unknown disease

The Scientific Committee has ruled out chemical poisoning and algae as an explanation for crustacean deaths in the northeast of England, saying a new disease is the most likely cause.

Massive crab die-offs seen in the northeast of England in 2021 and 2022 could be caused by a never-before-seen disease, a scientific committee set up by the UK Department for the Environment, Food and Rural Affairs (Defra) has concluded. The committee concluded that it was unlikely that algae or chemical poisoning was responsible for the deaths, as previous studies had suggested.

In October 2021, tens of thousands of dead and dying crabs and lobsters began washing ashore along the Tees Estuary on the North Yorkshire coast and then further south in the fishing town of Whitby. In May 2022, a death investigation by Defra pointed to a rapid natural increase in ocean algae, also known as algal blooms, as a potential cause of the deaths. But the investigation also acknowledged that it did not find a single causal factor in death.

In October, a group of researchers commissioned by the fishing team published their own study of mass deaths. The team argued that they were unlikely to have been caused by algal blooms and instead suggested that the more likely cause of death was a release of pyridine into sediments that had been excavated to make way for a new freeport on the River Tees.

UK Environment Minister Teresa Coffey ordered Defra to set up an independent scientific committee to look into the matter further. The committee has now said that no single factor can be blamed for the mass mortality of crustaceans. Instead, it is estimated that there is a 33 to 66 percent chance that the mass death was caused by a new disease that only affects crabs and lobsters.

Tammy Horton of the UK’s National Oceanographic Centre, who was on the committee that wrote the report, said at a press briefing that the new disease could explain why the crabs twitched when they died.

This also explains why the mass deaths took so long, and the fact that other marine life was not affected, Horton said. However, direct evidence of a new disease has not yet been found, she added.

The report ignores Defra’s initial suggestion that algal blooms were to blame for the death of the crabs, saying that this cannot explain the twitches seen in the crabs. “I am not nitpicking the earlier report,” Defra chief scientific adviser Gideon Henderson said at the briefing. “As usual in science, our knowledge deepens over time.”

The committee also stated that the duration of the mass deaths ruled out pyridine poisoning. “That ended the pyridine story,” says Crispin Halsall of Lancaster University, UK, another member of the committee. “You need a constant large source of pyridine to cause this. [crab deaths] and that is clearly not the case.”

The report states that the last time before the Tees mass extinction was dredging was in December 2020, and no further dredging took place in the region until September 2022.

Henderson said if the disease is a major factor in the death of crabs, it’s hard to say if it’s still causing more deaths in the region. “As more people become aware, people are reporting [crab deaths] more often,” he said. “It’s hard to tell if this is unusual until we put all the data together.”

Horton said the disease is unlikely to be dangerous to humans as it only seems to affect crabs. “Seafood is safe to eat,” she says.

Rodney Forster of the University of Hull, UK, who was involved in the second crab death report, which ultimately blamed dredging, says the new report is good and thorough, and that he largely agrees with its findings. He says the debacle over this issue has highlighted the flaws in the UK’s water monitoring system. “We have a reactive system, not a proactive one,” he says.

Forster says that due to government budget cuts, water quality in the UK is measured only at the surface and not at the seabed where the crabs live. Levels of toxic algae are also not monitored in areas of the UK that are not used to grow oysters and mussels, he said. The lack of monitoring is a major reason why we still don’t know what exactly caused these crab deaths, he said.

“I think we underestimate the importance of having healthy and safe rivers,” says Forster. “We have to measure certain parts of the marine system to understand it – we have to be prepared for climate change.”