When tourists visit a new location, they often want to try the local cuisine. But when toxins enter the marine ecosystem, there’s a risk that regional seafood delicacies can become dangerous for humans to ingest.

To prevent this, marine researchers at CCMAR-Algarve are using data from the analysis of trumpet shells (Charonia lampas) to detect an emergent neurotoxin called TTX so they can try to prevent people getting sick from eating contaminated gastropods.

Sandra Lage, research group leader at CCMAR, University of Algarve (EMBRC Portugal) explains why this is important and how toxins accumulating in ocean organisms affects communities, tourism, and economies – not just the marine environment.

Tetrodotoxin (TTX) is a neurotoxin found in some marine animals. It is most commonly associated with fugu (blowfish), which is used in sushi. Consuming contaminated fish can lead to cardiac arrest and even death.

TTX was previously only detected in Asian countries but is now considered an emerging toxin in Europe. During the 2000s, TTX started to be detected in European waters due to an invasion of non-native pufferfish that migrated into the Mediterranean from the Red Sea via the Suez Canal. Consumption of these species was banned to keep people safe.

In 2007, a man got sick after eating a trumpet shell and researchers discovered that these molluscs could also contain this dangerous toxin. Scientists were able to trace the trumpet shell back to the south coast of Portugal – they found trumpet shells in markets with concentrations of TTX that were unsafe for human consumption.

Working together with local fishers, we collected trumpet shells for a year and analysed them for the presence of TTX. It was found in unsafe levels in 76% of these snails, and it’s also found in other molluscs, including mussels, across Europe. But the European Food Safety Authority concluded that there was not yet enough data to develop a monitoring programme or regulations for this toxin.

The European Food Safety Authority said that organisms with 44 micrograms per kilo of meat are safe to consume. Anything above that was too high. Our trumpet shell samples had concentrations up to 1600 times above this. Although the levels varied throughout the year, they were always over this safe level of 44 micrograms. It looks like higher bottom seawater temperatures may play a role in increased values of this toxin, but we’re not sure exactly how it influences the levels.

During our analysis, we found TTX exclusively in the snail’s viscera (internal organs), not the muscle. If you dissect it correctly, it would be safe to consume the meat. But these organisms are sold whole in the market, including the shell. To get to the meat, you need to break the shell and it’s not easy for inexperienced people to do this while keeping the soft tissues intact. If, somehow, you break the viscera, this toxin contaminates the muscle. Cooking or freezing won’t degrade the toxin and it will pass into the water if you’re boiling it – often a traditional form of cooking molluscs. That’s why preparing the seafood correctly is important, not just forbidding the consumption.

We knew that the toxin must come from somewhere – but where? One possibility is bacteria. While collecting the trumpet shells, we gathered sea stars – one of their main prey items – from the same location. When we tested them, we found that they also contained TTX but at lower levels, which is aligned with the theory of bioaccumulation.

We concluded that the sea star is a potential source of contamination for the trumpet shell, but not the only one. We’re still looking for other potential vectors.

This is a great example of the real-life impact monitoring and studying the marine environment can have on communities and economies.

Some marine biotoxins are regulated but, to put legislation in place, we need enough data. A lot of the emergent toxins that weren’t previously present in Europe are associated with tropical regions so they’re not monitored for or regulated in Europe. Studying them is vital because, without data, decision-makers can’t put regulations in place to protect people and prevent a widespread public health issue.

In the little data that we have so far, we’ve seen very high concentrations of TTX but we don’t want to create panic before we know the full picture of which organisms in which regions could be dangerous.

Trumpet shell is considered a delicacy in the Algarve but a lot of tourists don’t know what they’re eating. We don’t know if other populations along the Atlantic coast of Portugal have the same issue. For example, one man got sick from eating trumpet shells in Spain but the animal he had eaten was fished in Portugal.

We need more data right now. That’s why we conducted a seasonal study over an entire year to try to confirm the results so we know whether vendors can continue to sell them safely in the market and what process they should follow to keep their customers safe.

My main objective is to create enough data to make science-based recommendations that change or inform legislation so people can safely consume these organisms and local suppliers can continue to benefit economically from a sustainable seafood industry. We don’t want to just forbid consumption. Ideally, there would be some legislation against selling the whole organism so that only the meat reaches the market.

For CCMAR, gathering this knowledge is such an important task, both for public health outcomes and to capture the attention of other researchers that might want to work on this area. Some marine scientists might not have the right expertise or instruments to explore this topic more but we can help with that through our EMBRC services. We can offer access to marine ecosystems and biodiversity, microorganism collections and model organisms, scientific diving, “omics”, bioinformatics and chemistry platforms.