Invasive flatworm devastates Adriatic shellfish farms alongside native predators

Marine biologists at the Piran Marine Biology Station have discovered that an invasive flatworm species, originating from the waters around New Zealand and Australia, is causing substantial damage to shellfish farms in the Adriatic Sea, compounding the impact of native gilt-head bream.

The flatworm, identified as Postenterogonia orbicularis, is proving to be a voracious predator across Europe's shellfish cultivation sites. It paralyzes bivalves with a toxin, allowing it to consume them. The organism is highly aggressive and reproduces rapidly, with each fragment capable of growing into a new worm.

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In the shell, instead of an edible mussel, there is a flatworm, similar to a crushed chewing gum.

In Slovenia, six shellfish farmers previously produced 700 tons of edible mussels annually. However, in recent years, their yields have been halved. This decline is attributed to both the native gilt-head bream, which crush shells with their powerful teeth, and the newly identified flatworm. The Slovenian state has responded by allowing special fishing quotas for bream in farming areas and providing compensation for damages.

Researchers, including biologist Andreja Ramšak from the Piran Marine Biology Station, have confirmed the flatworm's presence in Slovenian waters, as well as in parts of Croatia and Montenegro. While other regions have not reported significant losses, the flatworm has caused dramatic crop declines in Italy. Ramšak suggests that shellfish farmers themselves may have introduced the invasive species to Europe by importing juvenile shellfish from the Pacific Ocean. The Interreg IPA Adrion project is also investigating this issue, with the Slovenian institute You Sea participating.

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They paralyze them with their toxin and open them.