Not only blue crab. The collapse of artisanal fishing in Venice lagoon is due to a different alien species: the sea nutwhose scientific name is Mnemiopsis leidyi. Some researchers discovered this in a study published in the specialized journal Hydrobiology. The sea walnut belongs to the phylum of ctenophores, marine organisms on average 10 centimeters large that resemble small jellyfish, but they have only a relative relationship with the latter, which are part of the phylum of Cnidaria. Only about a hundred species that belong to the Ctenophores are known, one of these is the sea walnut.
Not just blue crab
«The study is the first example of quantifying the impact that a invasive species has had and unfortunately is still having on small-scale lagoon fishing”, says Filippo Piccardi, first author of the research and doctoral student at the University of Padua. «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».
Environmental and social tragedy
«Invasive species such as sea walnut and blue crab are one environmental and social tragedy which must be addressed by seeking sustainable mitigation and adaptation strategies”, adds Alberto Barausse, research coordinator. Sea nuts, small and gelatinous like jellyfish, clog the fishing nets of the small traditional fishermen of the lagoon
The help of lagoon fishermen
«This project», continues Piccardi, a doctoral student in the European Pon research and innovation programme, «was born from the collaboration between researchers from the Chioggia branch of the University of Padua and lagoon fishermen. They were the first to see the intruder in the lagoon around 2010 and to suffer the consequences. Statistical modeling clarified how the sea nut explosion in 2014 coincides with a significant increase in the temperature of lagoon waters.”
