It is called a sea nut and resembles a jellyfish: this alien species arrived in the Venetian lagoon in 2010 and then exploded in 2014 causing serious damage to the fragile local ecosystem and fisheries.
It’s small enough to fit in the palm of your hand and is practically Invisibleyet it is seriously endangering the biodiversity of the Venetian lagoon. We are talking about the “sea nut”, an alien species that has arrived in the waters of Adriatic sea more or less in 2010 due to climate change.
Its scientific name is Mnemiopsis leidyicomes fromAtlantic Oceanand despite its harmless appearance – it has a gelatinous consistency, similar to that of a jellyfish, but is not dangerous for humans – it is becoming thefishermen’s nightmare who use i cogolian ancient traditional fishing technique from the Venice lagoon.
As often happens with invasive alien species, the sea walnut feeds on the local fauna, creating a serious imbalance in ecosystems and threatening biodiversity. Now, a study conducted by researchers from the Chioggia branch of theUniversity of Padua with the National Institute of Oceanography and Experimental Geophysics of Trieste and the participation of local fishermenwas the first to measure its presence and the phases of its settlement in the lagoon.
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How the sea walnut arrived in the Venetian lagoon
History repeats itself and will probably repeat itself again, at least until truly effective measures are put in place to contain it warming of the seas as a result of the climate crisis: as happened with the blue crab – whose presence grew so much that the animals began to eat each other – climate change and the consequent increase in sea temperatures they certainly played a decisive role. It must also be said that the heavy naval traffic, one of the main access routes for non-native species, makes the lagoon an area at risk for biological invasions.
As regards this specific case, the sea nut covers theidentikit of the perfect invader: because it is practically invisible, it reproduces at an intense pace and feeds on plankton and larvae of local species, including also some very valuable varieties and vital to the survival of local fisheries.
The impact on local fisheries
In fact, it was precisely the fishermen who observed in recent years that something in the sea was changing. The first, alarming clue: the progressive decline in the catch. Just as the fish in the nets began to decrease more and more, there are cthe first sea nuts appearedwhich with their gelatinous consistency clog the mesh of the nets, creating a sort of barrier that hinders fishing itself.
The statistical models created by researchers at the University of Padua have reconstructed what happened: it is likely that the first sea nuts arrived in the Adriatic Sea as early as 2010, and then explode in 2014. Since then the caught has become less and less abundant: it is estimated that between from 2014 to 2019 it almost halved (-40%). Given that the blue crab was not yet there at the time – the researchers hypothesize – the coincidence between the increase in the presence of the sea nut and the fishing crisis in the lagoon cannot be coincidental.
“A social and environmental tragedy”
The presence of the sea nut is a problem from several points of view. The study authors called it one “social and environmental tragedy” which requires immediate sustainable solutions to mitigate its effects. “Social” because it risks the disappearance of a thousand-year-old and sustainable fishing tradition, i.e. cogoli fishing, but above all “environmental”, as invasive species are a serious threat to biodiversity and local ecosystems.
