A strange marine creature called the warty comb jelly has invaded Venice’s network of lagoons and is wreaking havoc on fish and other native species.
The gelatinous creature, also known as the sea walnut, normally lives in the western Atlantic.
But it has managed to colonise large tracts of the Adriatic, likely after being accidentally transported there in the ballast water of ships.
In a new report, scientists say its successful proliferation is a result of “ongoing climate change”, which has led to warmer water temperatures and optimal levels of salinity.
Until now, the marine animal’s main claim to fame is that it has a transient anus – an opening that only appears during the act of defecation. It is also known to eat its own offspring.
Scientists say there has been an explosion in the number of jellyfish in Venice’s lagoon, and it is presenting acute challenges for Venetian fishermen.
Not only does the warty comb jelly clog up fishing nets because of its squishy, gelatinous nature, but it is also a voracious predator that eats fish eggs, fish larvae and plankton – the building blocks of the lagoon ecosystem.
The jellyfish, Latin name Mnemiopsis leidyi, is considered to be one of the 100 most harmful invasive species in the world.
It is now present throughout much of Venice’s lagoon, according to scientists from the University of Padua and the National Institute of Oceanography and Applied Geophysics, who published the results of a two-year study in the journal Estuarine, Coastal and Shelf Science.
The invasive species is creating “serious issues” for the fishing sector, which is worth billions of euros in the Adriatic, they say. The region is particularly well known for its production of clams and mussels.
“Ongoing climate change could create increasingly favourable environmental conditions for this ctenophore, potentially boosting its presence in large aggregations and, consequently, increasing the risk of impacts on the entire lagoon ecosystem,” the scientists said in their report.
The best-known invasive species in the Adriatic is the blue crab, which also comes originally from the Atlantic.
It too was likely introduced accidentally to the Adriatic in the ballast water of cargo ships.
Named for its vivid blue claws, it uses them to tear into clams, mussels, prawns and other seafood.
The crabs are known to wreck fishing nets, eating the fish trapped inside and causing millions of euros worth of damage.
Italy is attempting to eat its way out of its blue crab invasion, and the species is increasingly being sold in supermarkets and appearing on restaurant menus.