Marine alien Mollusca in the Gulf of Trieste and neighbouring areas: a critical review and state of knowledge (updated in 2011)

Biological pollution is recognized worldwide as one of the main threats to biodiversity, the economy and human health (ElliOTT, 2003). The opening of the Suez Canal in 1869 has led to the colonization of the Mediterranean Sea by a large number of tropical/subtropical species that have established viable populations along the The state of knowledge on marine alien molluscan species from the Gulf of Trieste and neighbouring areas is presented based on a critical review of records compiled from an extensive literature survey and from unpublished data obtained from 2006 to 2011, and enriched by older material preserved in private collections. Based on the IUCN definition of ‘alien’, 13 valid alien molluscan taxa (3 Gastropoda and 10 Bivalvia) are reported here, for each of which the following information (collected up to August 2011) is provided: published and unpublished records from the coastal and offshore territorial seawaters of the Gulf of Trieste and neighbouring areas, including lagoons; establishment status; vector(s) of introduction. The area was characterized by the presence of eight established alien species, while another four were considered as casual and one was, with caution, considered not established. Specimens of Anadara transversa (Say, 1822) and limnoperna securis (Lamarck, 1819) are first reported here from the Gulf of Trieste, thus reaching the extreme northern point of the Mediterranean Sea. Old distribution data on Mercenaria mercenaria (Linnaeus, 1758) and Mya arenaria Linnaeus, 1758 are considered unreliable, also according to the recent literature. Accurate analysis of bibliographic data as well as re-identification of specimens preserved in private collections or collected from the same published sampling sites led to the exclusion of Assiminea grayana Fleming, 1828 and Conomurex persicus (Swainson, 1821) from the resident fauna of the Gulf of Trieste. Concerning Arcuatula senhousia (Benson in Cantor, 1842), its first record from Slovenia came from bibliographic misreading, so that the original record of this bivalve from the area is considered more recent. Finally, natural dispersal accounts for 46% of the plausible vectors of introduction, while shipping/maritime transport and aquaculture for 23%.