Two strains of the bacteria – Vibrio rotiferianus and Vibrio jasicida – which have never been recorded in the UK’s shallow waters before were discovered in the harbour.
Because shellfish are filter feeders, levels of the pathogen can build to significantly higher concentrations in their tissues compared with 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 is ingested.
Vibrio can also cause skin infections if the bacteria enter the body through cuts and abrasions.
Researchers used Met Office data to find areas where sea-surface temperatures reached between 13C and 22C, which is favourable to the growth of the various Vibrio species.
They then analysed samples from four shellfish farms located in these areas, namely Chichester Harbour, Osea Island, Whitstable Bay and Lyme Bay.
Vibrio parahaemolyticus, the most common cause of seafood-borne gastroenteritis worldwide, was found at Chichester Harbour.
The strain Vibrio alginolyticus, which causes wound infection and the ear infection otitis, were found at Chichester Harbour, Osea Island and Whitstable Bay.
These three sites had sea-surface temperatures of above 18C for a number of weeks each year.
‘It is important to note that thorough cooking kills harmful Vibrio bacteria in seafood,’ Dr Sariqa Wagley, of the University of Exeter
‘However, increasing abundance and diversity of Vibrio bacteria creates health risks not only for people eating seafood, but for those using the sea for recreation purposes – either due to swallowing infected seawater or from the bacteria entering exposed wounds or cuts.’
She continued: ‘Vibrio bacteria are also a threat to a variety of marine species including shellfish themselves.
‘Disease costs the global aquaculture industry £6bn a year, and this burden of disease can be devastating.
‘We have not seen mass mortality of shellfish due to Vibrio bacteria here in the UK yet, but this has occurred elsewhere – including in France and Australia.’
Vibrio rotiferianus was found in four samples gathered from Chichester Harbour, while Vibrio jasicida was found in eight samples.
It is the first time these two strains of the Vibrio bacteria have been detected in the UK.
Dr Wagley said the situation needed to be monitored ‘closely to protect human health, marine biodiversity and the seafood industry.’
Dr Luke Helmer, from Blue Marine Foundation and the University of Portsmouth, added: ‘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 the people that rely on them will be crucial moving forward, in order to mitigate against them.’