Blue crab threatens clam production in the Po Delta

The blue crab (Callinectes sapidus), a species native to the western Atlantic, is notorious for its voracious appetite and adaptability to various habitats. It has rapidly spread across the northern Adriatic lagoons. A recent study by the Italian Institute for Environmental Protection and Research (ISPRA) revealed record densities of this invasive species during the summer 2023. Alarmingly, ovigerous females accounted of 19.2% in July, highlighting their exceptional reproductive capability.

The Po Delta, a major hub for Manila clam (Ruditapes philippinarum) farming in both Italy and Europe, is facing an unprecedented crisis. The blue crab invasion has severely impacted the local economy of the Sacca del Canarin and Sacca degli Scardovari lagoons. Since spring 2023, fishers and aquaculture farmers have reported significant losses, with mortality rates among clams reaching 100% in some zones. This unsustainable situation has left many local shellfish harvesters without a livelihood.

The data paints a grim picture. In Sacca del Canarin, Manila clam production has plummeted by nearly 100%, while Sacca degli Scardovari has seen a drop of over 75%. This amounts to a loss of approximately 1,000 tonnes of clams within just three months, with an economic impact exceeding €250 million annually, according to local producers.

The repercussion extends beyond production losses. The cost of capturing and disposing of the crabs has surged, and the need to import clam seeds from the United States and Portugal has driven up prices. This reliance on foreign imports also raises the risk of introducing new invasive species. Additionally, the crabs’ predation threatens local biodiversity, impacting other marine species.

Experts warn that the future of the clam industry in the Po Delta hinges on a coordinated response involving authorities, scientists, and the local community. In the meantime, aquaculture farmers are grappling with the harsh reality of an ecosystem that is rapidly under the strain of an invader that is here to stay.