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US invader threatens Portugal’s shellfish industry

Published on 18/12/2017

The mussel and oyster sector of Portugal sea economy is on high alert after researchers from the Portuguese Institute of the Sea and Atmosphere (IPMA), located a foreign invasive species that poses a serious threat to stocks.

Portugal also has put producers along Spain’s Galician coast on alert due to the rapid proliferation of the Ascidia Styela plicata, or ‘sea squirt,’ which competes directly for food with native shellfish and munches its larvae.

Styela plicata is from the east coast of the USA and from the Caribbean. Enormous numbers found in the Gulf of Mexico has led to it being categorised as a plague.

Portugal now has joined the list of infected European countries that includes Italy, Greece and the United Kingdom. Such is the little chap’s ability to hitch a ride on hulls, it has been found in the Mediterranean, Australia, the east coast of South America, Japan, Hong Kong, the Indian Ocean and the west coast of the USA.

Styela plicata is a benthic species, living on the bottom of the aquatic ecosystems, is resistant to changes in water temperature, in alterations to the salinity of seawater and to pollution.

The IPMA reported that the latest finding occurred on 21 September this year, when the species was identified at a shellfish production facility in the Laguna de Albufeira, Sesimbra. Previously, the species had been spotted in the Tajo estuary, in the Algarve and in Peniche.

The institute warned that Styela plicata has a rapid, three month breeding cycle and that it can not be eradicated.

The Portuguese scientists explained that this exotic species does not have a negative effect on human health, so the damage it causes is to existing shellfish beds where it competes for food and eats shellfish larvae.