This story from Italy about the invasion of blue crabs which has devastated a historical fishing industry, demonstrates the human and economic cost of marine pest establishment.
Sacca degli Scardovari - Delta del Po / GitoTrevisan iStock
In the Po River Delta in northeastern Italy, generations of families have earned their living harvesting Manila clams from the region's lagoons. But since 2023, an explosion in the population of invasive Atlantic blue crabs has transformed the industry.
The crabs, native to the Americas, feed on shellfish, crushing their shells with powerful claws. In the Scardovari lagoon, annual clam harvests have fallen by 93%, and more than 600 fishers have left the industry, according to a July 2026 CNN report.
The blue crabs are thought to have originally arrived in the Mediterranean through ships' ballast water. Although they have been present for decades, warmer waters and changing environmental conditions have helped their populations expand rapidly.
Efforts to control the crabs have included large-scale harvesting and attempts to develop a commercial market for them. Some fishers are now selling the crabs for export, although this has yet to replace the income previously generated by the clam industry.
The experience demonstrates how quickly an established marine pest can become a serious problem when conditions favour its spread, with consequences that extend well beyond the marine environment.