First record of Mnemiopsis leidyi (Ctenophora, Bolinopsidae) in Sardinia (S’Ena Arrubia Lagoon, Western Mediterranean): a threat for local fishery?

The invasive comb jelly Mnemiopsis leidyi is a lobate ctenophore native of coastal and estuarine waters in the temperate west- ern Atlantic Ocean. Over the last decades, this species has expanded its range of distribution, colonizing marine and transitional environments in Europe. In October 2015, during a fishing survey concerning the European eel Anguilla anguilla in Sardinia (western Mediterranean), a massive bloom of this species was observed in the eutrophic S’Ena Arrubia Lagoon for the first time. In November 2015, two sampling tows of an Apstein net were conducted in the lagoon and the abundance of ctenophores was 2.83 ind. m-3. All collected specimens were adults, measuring 18 - 62 mm total length. In addition, a fyke net was deployed for 12h in order to roughly estimate the impact of the ctenophores on the fishing activity. The high number of ctenophores (6837 individu- als per fyke net) in the net suggests a negative effect on fishing operations by reducing catches and affecting the performance of fishing gears. Since there is no effective mechanical, chemical or biological method to counter M. leidyi, the short-term economic damage may be addressed by new fisheries management measures, as well as by reducing the eutrophication of the lagoon.