INVASIVE SPECIES

Manila clam in North Adriatic: Million-euro sector at risk from invasive Blue Crab

Venice, Italy, 12 August 2025 | Researchers warn of severe economic losses unless urgent control measures are taken

Cangrejo azul en pescadería

The Northern Adriatic’s thriving Manila clam (Ruditapes philippinarum) industry, worth over €60 million annually, is facing a growing threat from an aggressive invader: the Atlantic blue crab (Callinectes sapidus).

Once confirmed to the western Atlantic, from Nova Scotia to Argentina, the blue crab has established stable populations in Italian waters since the early 2000s. In the Po Delta-Italy’s most important clam farming area-the species’ recent population boom has raised alarms among scientists and producers alike. Its powerful claws, high reproductive rate and adaptability make it a formidable predator, capable of damaging fishing gear and outcompeting native species.

A new study by Ca’ Foscari University of Venice, published in Estuarine, Coastal and Shelf Science, has provided the first detailed look at the blue crab’s feeding behaviour on Manila clam. Through controlled laboratory experiments, researchers observed that both male and female crabs prefer small clams under 35 mm-the seed stock essential for future harvest-opening them mainly by crushing their shells. Males were found to consume more clams than females, averaging eight per day versus five.

The risk is not hypothetical. In some Po Delta lagoons in 2023, clams losses reached 100%, with signs of blue crab predation and an absence of natural juvenile recruitment. If seed beds are depleted, the long-term viability of the sector is at stake.

Expert are calling for urgent action, including selective protection of seed beds, targeted harvesting of blue crabs, and research into deterrents. In other Mediterranean regions, such as Tunisia and Turkey, the species has been turned into a commercial resource, but Italian producers fear that without rapid containment, the damage to clam farming will outweigh any potential benefits.

With the Ministry of Agriculture estimating €40 million in emergency support needed for farmers in 2023 alone, the battle to protect the Northern Adriatic’s Manila clam industry is as much an economic imperative as an environmental one. The coming years will determine whether this valuable resource can be safeguarded-or whether the blue crab will continue its march unchecked.

Reference:

Pasquini, L., Navone, A., Perin, S., Giani, M., & Mistri, M. (2025). Handling time and predation rate of the invasive blue crab Callinectes sapidus on different size classes of the Manila clam Ruditapes philippinarum. Estuarine, Coastal and Shelf Science, 300, 109620. https://doi.org/10.1016/j.ecss.2025.109620