In the Philippines, we are worried. The country, the eleventh largest producer of seafood in the world, was surprised to learn of the discovery of two species of microscopic algae in samples of shellfish, all from farms in the region. The news concerns coastal communities, which depend on this industry: the tropical waters of the archipelago supply more than four million tonnes of seafood to global markets.
The algae observed in Philippine shellfish are diatoms. They produce glass “shells” that are like tiny living jewels. Problem: Of the millions of existing diatom species, twenty-eight of the genus “Pseudo-nitzschia” are known to produce a harmful neurotoxin called “domoic acid.” And you definitely don’t want to find this substance on your plate, warns online media ScienceAlert.
“It is important to be aware of the toxic potential of these diatoms and monitor them accordingly”let the authors know of a study published in October 2024. Domoic acid can accumulate in particular in shellfish, sardines and anchovies, because their diet consists mainly of marine algae such as diatoms.
Rest assured, it is extremely rare for seafood loaded with this toxin to reach our tables. However, human activities are causing more frequent marine algae blooms, which increases the risk. Seafood could thus accumulate more domoic acid, at levels that produce quite worrying side effects, ranging from vomiting to amnesia, or even, in the worst cases, death.
Blue mussels and giant oysters
In 1987, three people died and at least 100 were hospitalized on Prince Edward Island, Canada, from amnesia caused by shellfish containing domoic acid. Because the latter can lead to permanent loss of short-term memory. At the time, the disaster was attributed to blue mussels (“Eating mussels”).
Since then, many industries have closely monitored Pseudo-nitzschia blooms, which explains why contamination is rare in many countries. But researchers from Ateneo de Manila University (Philippines) and University of Malaysia Sarawak (Malaysia) found that more work is needed in the Philippines. Scientists have in fact found these diatoms responsible for amnesia in shellfish from marine farms located off the island of Luzon (north of the archipelago), densely populated – more than half of the Philippine population.
However, in this Southeast Asian country, molluscs and crustaceans constitute the cornerstone of the diet of many inhabitants. The team collected seawater samples from Sotto’s Tahong Farm in Bacoor Bay, which supplies mussels to Manila (the capital) and neighboring provinces. But also in Pagbilao Bay, which is home to a natural population of giant oysters («Magallana bilineata»)grown in coastal towns and fishing villages.
The researchers isolated fifteen strains of Pseudo-nitzschia from seawater and grew them in the laboratory. Through genetic analysis, they found two species of algae in the samples: ‘Pseudo-nitzschia pungens’ and ‘Pseudo-nitzschia brasiliana’, both of which produce domoic acid. It is hoped that this discovery will help producers monitor future harmful algal blooms, and thus limit future outbreaks of amnestic shellfish poisoning.
Source: www.slate.fr
