New research has found that rising temperatures in UK waters are causing an uptick in bacteria linked to gastroenteritis in humans.
Various strains of potentially harmful Vibrio bacteria have increased.
The researchers, led by academics from the University of Exeter, also found two strains, Vibrio rotiferianus and Vibrio jassicida, that had never been previously recorded in the shallow waters of the UK.
Because shellfish are filter feeders, levels of the pathogen can build up in significantly higher concentrations in their tissues than in the surrounding water.
Vibrio bacteria have been linked to mass die-offs in wild and farmed oysters, and can cause gastroenteritis in humans if raw or undercooked shellfish are consumed.
Vibrio can cause skin infections if the bacteria enter the body through cuts and abrasions.
The researchers found that there has been an increase in vibriosis infections in humans and aquatic animals in recent years.
Dr Sarika Wagle, from the University of Exeter, said: “Vibrio species can often be found in UK waters in the summer, when temperatures are more favorable for them.
“With the increase in sea surface temperatures due to climate change, Vibrio activity in water is more common, and the diversity of Vibrio species is now increasing.”
The research team used Met Office data to find locations where sea surface temperatures were reaching between 13C and 22C, which are favorable for the growth of various Vibrio species.
They then analyzed samples from four shellfish farms located in these areas, namely Chichester Harbor, Oceania Island Whitstable Bay and Lime Bay.
Vibrio parahaemolyticus, the most common cause of seafood-borne gastroenteritis worldwide, was found in Chichester Harbor.
The strain Vibrio alginolyticus, which causes wound infection and ear infection otitis, was found in Chichester Harbor, Oceania Island and Whitstable Bay.
These three sites had sea surface temperatures above 18C for several weeks each year.
“It’s important to note that thorough cooking kills the harmful Vibrio bacteria in seafood,” Dr. Wagley said.
“However, the increasing abundance and diversity of Vibrio bacteria pose a health risk not only to people who eat seafood, but to those using the ocean for recreational purposes – either by swallowing infected seawater or in wounds exposed to the bacteria or Because of entering the cut.”
She continued: “Vibrio bacteria are also a threat to a variety of marine species, including shellfish.
“Disease causes the global aquaculture industry to lose £6 billion annually, and this burden of disease can be devastating.
“We have not yet seen a mass death of shellfish due to Vibrio bacteria in the UK, but it has happened elsewhere – including France and Australia.”
Vibrio rotiferianus was found in four specimens collected from Chichester Harbor and Ocean Island, while Vibrio jasicida was found in eight specimens collected from Chichester Harbor and Whitstable Bay.
This is the first time these two strains of Vibrio bacteria have been detected in the UK.
Dr Wagley said: “Our findings support the hypothesis that diseases associated with Vibrio are on the rise and are influenced by increased sea surface temperatures.
“We need to monitor this situation closely to protect human health, marine biodiversity and the seafood industry.”
Dr Luke Helmer, from the Blue Marine Foundation and the University of Portsmouth, said: “The impacts of climate change on the marine environment are likely to be widespread.
“Understanding how these changes will affect ecologically and commercially important species and those who rely on them will be critical to moving forward to mitigate against them.”
The UK shellfish industry was worth £350 million in 2019, according to government figures, but around 95% of native oyster reefs have been lost.
In Chichester Harbor, the population of native wild oysters fell by 96% between 1998 and 2017.
While it cannot be proven that Vibrio bacteria are behind the decline, the report’s authors stress that it was important to take a “one health” view of marine ecosystems.
The approach considers all environmental stressors, including sewage leaks, high concentrations of harmful chemicals, and increasing numbers and stresses of animal and human pathogens.
The study, the increasing prevalence of Vibrio species and the first reporting of Vibrio jascisida and Vibrio rotiferianus at UK shellfish sites, is published in the journal Water Research.
The research was funded by the Biotechnology and Biological Sciences Research Council (BBSRC), and supported by Chichester and Havant Council and the Sussex Inshore Fisheries and Conservation Authority.