Climate change affecting oyster industry

Charles Darwin University (CDU) environmental microbiology researchers have presented research focused on understanding tropical rock oysters, Vibrios and the implications for food safety and human health at an international Aquaculture conference in Darwin.

The research was presented by Dr Anna Padovan and Professor Karen Gibb from CDU Research Institute Environment & Livelihoods at the International Tropical Rock Oyster Workshop, part of the World Aquaculture Conference 2023.

Vibrio bacteria occur naturally in aquatic habitats, especially coastal areas and estuaries. They are associated with waters warmer than 15°C, which is the case in the tropics.

This research, funded by the Fisheries Research Development Corporation, was of high priority given the increasing interest in developing a tropical rock oyster industry in Northern Australia.

“We urgently need to learn more about this bacteria, its growth rates and how pathogenic strains can suddenly dominate the bacterial population in both seawater and shellfish to adversely affect food safety and human health,” Padovan said.

Over 40 Vibrio species were detected in northern waters, but few of those had the potential to threaten animal or human health. Different strains were also detected in the few species that are potential pathogens.

The pathogenic bacteria can have an adverse effect on humans either through contact with seawater and marine animals or through the ingestion of raw, undercooked or temperature abused shellfish.

There has been a global increase of illnesses like gastroenteritis associated with Vibrio bacteria, which has been attributed to climate change where Vibrio bacteria can colonise new areas on warm currents.

“Even for those known pathogenic Vibrio species, not all strains of that species are a problem. But we urgently need to do more work on those pathogenic strains to find out what genes enable them to cause illness,” Padovan said.

Some genes are known, but they are not always present in human clinical samples, so there are more to find. The genes can be used to develop mobile testing capability to provide early warnings that pathogenic strains are present.

Gibb, Padovan and their team have been working on Vibrios in Northern Australia for over 10 years. In that time, they have measured Vibrio levels in seawater and molluscs, including oysters, finding that pathogenic strains occur in less than 3% of samples.

They identified a diversity of Vibrio species and found that they are influenced by temperature, salinity and nutrients.

“We’re only beginning the journey to understand pathogen genes, but this will be key to understanding when and how Vibrios cause illness in people,” Padovan said.

With greater understanding, the researchers will be able to make more significant contributions to quality assurance for the Northern Australian tropical rock oyster industry.

At the conference, the team presented findings on tropical Blacklip Rock Oysters and the growth rates of potential pathogenic Vibrio at temperatures likely to be encountered post-harvest.

Zarah Tinning, a PhD candidate funded by the CRC Developing North Australia, also spoke, with her talk focusing on the health of Tropical Rock Oyster larvae which are also impacted by Vibrio bacteria, to overcome hatchery bottlenecks.