A recent study has revealed that the collapse of artisanal fishing in the Venice lagoon is not due to sea nuts more than to the blue crab
The collapse of artisanal fishing in the Venice lagoon is not only due to the presence of the blue crab, but also to that of another alien species: the sea nut. This was discovered by some researchers who published a study in the authoritative specialized journal ‘Hydrobiologia’.
The results of the study
The fishing crisis in the area Venice lagoon had been attributed almost exclusively to the blue crab awakened by the heat in Veneto: this species certainly contributed to the collapse, but the sea walnut did it even more, as highlighted by a recent study. Filippo Picardi, first author of the research and doctoral student at the University of Padua, elected one of the best universities in Europe, spoke about the discovery:
“The study is the first example of quantifying the impact that an invasive species has had and unfortunately is still having on small-scale lagoon fishing – the words of Filippo Picardi reported by the ‘Corriere della Sera’ – there is not only the blue crab and the risk of these biological invasions is that of the total loss of an almost thousand-year-old lagoon fishing tradition that uses extremely sustainable gear”.
Picardi recalled that the project was born “from the collaboration between researchers at the headquarters Chioggia of the University of Padua and lagoon fishermen. Statistical modeling clarified how the sea nut explosion in 2014 coincides with a significant increase in the temperature of lagoon waters.”
The research coordinator, Alberto Barausse, explained that invasive species such as the sea nut and the blue crab represent “a environmental tragedysocial ee that must be addressed, seeking mitigation and adaptation strategies that are sustainable”.
Sea nuts and the collapse of fishing in the Venice lagoon
The scientific name of the sea nut is Mnemiopsis leidyi: this alien species belongs to the phylum of ctenophores, marine organisms on average ten centimeters large that resemble small jellyfish even if they have only a relative relationship with the latter, belonging to the phylum of Cnidaria. Like jellyfish, they are small and gelatinous: they clog the fishing nets of the small traditional fishermen of the lagoon, putting the entire sector in crisis.
Mnemiopsis leidyi is native to the Atlantic but, as happened with other alien species, it managed to enter the Black Sea through the ballast water of tankers, where it has been observed since the 1980s. A decade later it also arrived in the Caspian Sea, before reaching the Aegean Sea and managing to colonize the entire Mediterranean Sea.
In Italy, sea nuts were reported sporadically in 2005 and then steadily from 2016 in the northern Adriatic, while the first reports in the Tyrrhenian Sea date back to 2011. These organisms live in shallow and eutrophic waters: they are very tolerant to climate change and therefore very resistant.
The ecological success of Mnemiopsis leidyi is mainly due to its extraordinary ability to use its cilia to generate a current that drags large volumes of water, without its prey being able to notice it. The propensity to stealthy predation makes the sea walnut a very effective predator: it is capable of capturing a vast range of microplantonic prey and fish larvae. Sea nuts are very effective predators and for this reason they are considered among the most invasive destructive species.
