BackgroundBivalve teredinids inflict great destruction to wooden maritime structures. Yet no comprehensive study was ever carried out on these organisms in European coastal waters. Thus, the aims of this study were to: investigate the diversity of teredinids in European coastal waters; map their past and recent distributions to detect range expansion or contraction; determine salinity-temperature (S-T) requirements of species; flag, for future monitoring, the species that pose the greatest hazard for wooden structures.ResultsA total of nine teredinid species were found established in European coastal waters. Seven were considered cryptogenic, of unknown origin, and two were considered alien species. Teredo navalis and Nototeredo norvagica were the species with the widest distribution in European waters. Recently, T. navalis has been reported occurring further east in the Baltic Sea but it was not found at a number of sites on the Atlantic coast of southern Europe. The Atlantic lineage of Lyrodus pedicellatus was the dominant teredinid in the southern Atlantic coast of Europe. In the Mediterranean six teredinid species occurred in sympatry, whereas only three of these occurred in the Black Sea. The species that pose the greatest hazard to wooden maritime structures in European coastal areas are T. navalis and the two lineages of L. pedicellatus.ConclusionsCombined data from field surveys and from the literature made it possible to determine the diversity of established teredinid species and their past and recent distribution in Europe. The environmental requirements of species, determined using climatic envelopes, produced valuable information that assisted on the explanation of species distribution. In addition, the observed trends of species range extension or contraction in Teredo navalis and in the two lineages of Lyrodus pedicellatus seem to emphasise the importance of temperature and salinity as determinants of the distribution of teredinids, whereas their life history strategy seems to play an important role on competition.Teredo navalis and pedicellatus-like Lyrodus species should be monitored due to their destructive capability. The two alien species may expand further their distribution range in Europe, becoming invasive, and should also be monitored.

Marine wood-boring teredinids, some of the most destructive wood borers in the sea, are a particularly difficult group to identify from morphological features. While in most bivalve species shell features are used as diagnostic characters, in the teredinids shell morphology shows high intraspecific variation and thus identification is based almost entirely on the morphology of the pallets. In the present study we aimed at improving ‘taxonomic resolution’ in teredinids by combining morphological evidence with mitochondrial and nuclear DNA sequences, respectively Cytochromec oxidase subunitI and small subunit rRNA 18S gene, to generate more rigorous and accessible identifications. DNA barcodes of Atlantic and Mediterranean populations of Lyrodus pedicellatus diverged by ~20%, suggesting cryptic species in the morphospecies L. pedicellatus. The low intraspecific divergence found in barcodes of specimens of Nototeredo norvagica (0.78%) confirms that Atlantic and Mediterranean forms of N. norvagica, the latter sometimes reported as Teredo utriculus, are the same species. Teredothyra dominicensis was found for the first time in the Mediterranean. A match was obtained between our 18S sequences and sequences of T. dominicensis from Netherlands Antilles, confirming that T. dominicensis in the Mediterranean is the same species that occurs in the Caribbean. There were differences in 18S sequences between Bankia carinata from the Mediterranean and Caribbean, which may indicate cryptic species.

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