Wooden groin systems on the southwestern Baltic Sea coast are a traditional and important coastal-protection facility, but have been regularly infested and destroyed by the wood-boring bivalve Teredo navalis since the early 1990s. The occurrence of T navalis was presumed to be limited mainly by the prevailing low salinities. Recently, a possible range expansion of this invasive species to the more eastern parts of the Baltic Sea has been discussed. T navalis larval settlement was therefore monitored at the distribution boundary of the species in the Baltic Sea over a period of 4 years. At 7 stations along the prevailing salinity gradient on the Mecklenburg-western Pomeranian coast, larval traps were installed at regular time intervals, while at the same time water temperature and salinity were measured continuously every hour. Correlations between measured abiotic parameters and borehole abundance of T navalis were tested. For the German Baltic Sea coast, no range expansion of T navalis was confirmed. The salinity and temperatures at the groin systems varied among the study years, and significant correlations between T navalis borehole abundance and salinity as well as temperature were found. Higher summer temperatures favor the T navalis borehole abundance on the Mecklenburg-western Pomeranian coast, and may slightly shift the distribution border of this species toward lower salinities.

The first documented scientific reports of the common marine shipworm Teredo navalis (Bivalvia) for Central European waters date back to the time between 1700 and 1730 in the Netherlands. During the following centuries there were several irregular mass occurrences reported for both the North Sea and the Baltic Sea. These events were accompanied by massive destruction of wooden ships and coastal protection structures. In this study, the first population analysis of T navalis is presented with the aim to detect the genetic population structure in the waters of Central Europe. The mtDNA COI (cytochrome c oxidase subunit I) locus was found as suitable molecular marker and hence a 675 bp gene fragment was studied. A total of 352 T navalis specimens from 13 different sampling sites distributed across Central Europe were examined. Subsequently, various population genetic indices including FsT values and an AMOVA analysis were applied for the description of the population structure. To visualize the distribution of haplotypes at the different sampling sites two median-joining networks were calculated. In addition, the past demographic structure of the T navalis population was analyzed, among others by calculating Tajima's D, Fu's F and the mismatch distribution. Finally, all computations of the population genetic indices could not reveal differentiated populations or any kind of distinct population structure in T navalis. The network analyses revealed "star-like" patterns without differentiated substructures or denies. Therefore, it can be assumed that a sudden expansion of this species took place without any indications of neither a bottleneck nor a founder effect for the study area. The results of this study support the concept of a regional panmictic population in the waters of Central Europe with unhindered migration of individuals (e.g., via pelagic larvae) between the various sampling sites as reflected by a high gene flow.

The common shipworm Teredo navalis is one of the most widespread marine wood-boring bivalves of the world and probably one of the most wood destructive and cost-incurring marine invertebrates. First reports on T. navalis for Europe date back to 1731 for the North Sea (The Netherlands) and to 1835 for the Baltic Sea (Germany). It is still unclear, however, where this species originates from. Therefore, T. navalis is considered cryptogenic for European waters, including the Baltic Sea.In this study, 181 specimens of Teredinidae from six different sampling areas all over Europe and North America were molecular-taxonomically investigated using several molecular markers, two nuclear (18S/28S) as well as one mitochondrial marker (cytochrome c oxidase subunit I, hereafter COI). For the COI gene amplification, a new specific primer pair (Ter fw II/Ter rev I) for T. navalis was developed, which allowed sequencing of a 675 bp COI gene fragment for the first time. For amplifying the COI gene fragment of other examined teredinids than T. navalis, a third primer (Ter fw III) was designed. These three new primers are valuable tools to identify teredinid species with the DNA barcoding approach.Classification of T. navalis into the system of wood-boring bivalves using a combined 18S/28S dataset showed no differentiation between specimens from Europe and the North American East Coast The results of the COI dataset analyses showed high haplotype diversity in combination with a low nucleotide diversity and a star-shaped network with a predominant haplotype occurring in all investigated regions. Moreover, no indications have been found on a sibling species in the Baltic Sea. The data indicate a recent population expansion for the examined sampling sites whereas the origin of the assumed worldwide distributed species T. navalis remains open. (C) 2015 Elsevier B.V. All rights reserved.

The naval shipworm Teredo navalis The naval shipworm, scientifically named Teredo navalis , destructively tunnels into almost all wooden structures in marine coastal habitats causing enormous economic damage. Already the early sailors feared this animal, because it destroyed their wooden ships, and even today the naval shipworm is responsible for high maintenance costs of all wooden coastal protection and harbour infrastructure. Nevertheless, there are still many open questions concerning the biology and the biogeographic origin of this species. In the Baltic Sea, where timber is widely used in coastal protection, Teredo navalis is considered as invasive species. Until now the eastern distribution is restricted to the Island of Hiddensee, due to the low salinity in this part of the Baltic Sea. One of the most important questions, however, is whether and how the observed climate change will affect the distribution of Teredo navalis .