In their analysis that goes back to 1958, the researchers show that levels of Vibrio bacteria – which can cause illness in humans and even death – have been increasing as sea surface temperatures rise.
Further ocean warming as a result of climate change could exacerbate this spread of marine bacteria, the researchers say, potentially bringing more human infections in the future.
Some of these bacteria cause sickness in people and animals. Humans pick them up by consuming water or seafood that carries the bacteria, or through cuts in the skin when swimming.
The most well-known Vibrio is cholera, a diarrhoeal disease that can cause severe dehydration and death if not treated.
This study considers other strains of Vibrio bacteria, such as Vibrio vulnificus and Vibrio parahaemolyticus, which cause similar, though usually less severe, symptoms. These types of illness are known collectively as “vibrosis”, which can lead to complications, such as blood poisoning.
The evidence is strong that ongoing climate change is influencing outbreaks of Vibrio infections on a worldwide scale.
Dr Luigi Vezzulli, lead author and associate professor in microbiology, University of Genoa
Previous research has linked outbreaks of Vibrio infections around the world to warm sea surface temperatures. Warmer conditions mean a longer summer window for Vibrio bacteria to grow and a greater chance of their survival. This conclusion has been reached in studies of Chile, Peru, Israel and the Baltic states.
The new study, just published in Proceedings of the National Academy of Sciences, says that a warming Atlantic Ocean is the main reason for an “unprecedented” number of Vibrio cases in North Atlantic countries in recent years. This includes a spate of cases contracted by swimmers during the European summer heatwave in 2006.
One of the main limitations for scientists trying to work out how ocean warming is affecting Vibrio bacteria is the availability of data.
Bacteria are typically measured by microbiologists by collecting and analysing water samples, says lead author Dr Luigi Vezzulli, an associate professor in microbiology at the University of Genoa. However, as he explains to Carbon Brief, this isn’t without difficulty: “This approach is costly and time consuming and historical Vibrio data are generally lacking.”
Vezzulli and his colleagues found a way round this problem by instead analysing samples of tiny marine creatures called zooplankton, on which Vibrio bacteria tend to hitch a ride.
Scientists have been collecting samples of plankton in the North Atlantic since 1958 via the Continuous Plankton Recorder (CPR) survey. The CPR actually gets its name from the instrument that, when towed behind ships, collects plankton over huge areas of ocean.
Using the samples from nine locations, the researchers analysed the DNA of the preserved plankton to create a record of how Vibrio bacteria numbers have changed over the past six decades.
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