First record of the Pacific oyster Magallana gigas (Thunberg, 1793) in the Baltic Sea proper

Since its introduction in the 1960’s for aquaculture, the Pacific oyster Magallana gigas (Thunberg, 1793) has successfully spread along almost all European coasts with far-reaching consequences for marine ecosystems. Up to now, it has not been recorded from the Baltic Sea proper. This was considered a consequence of the low salinity conditions, which are not suitable for larval development. Here we report our first records of Pacific oysters in the German Baltic Sea, specifically in the Kiel Bight. We confirmed their species identification by genetic barcoding. We suggest that Pacific oysters were able to settle in the Baltic Sea proper due to unusually high salinities that prevailed since the summer of 2018. Should these conditions occur more frequently in the future, or M. gigas be able to adapt to lower salinities, oysters may become established in the Baltic Sea proper

Phylogeography in an "oyster" shell provides first insights into the genetic structure of an extinct Ostrea edulis population

The historical phylogeography of Ostrea edulis was successfully depicted in its native range for the first time using ancient DNA methods on dry shells from museum collections. This research reconstructed the historical population structure of the European flat oyster across Europe in the 1870s-including the now extinct population in the Wadden Sea. In total, four haplogroups were identified with one haplogroup having a patchy distribution from the North Sea to the Atlantic coast of France. This irregular distribution could be the result of translocations. The other three haplogroups are restricted to narrow geographic ranges, which may indicate adaptation to local environmental conditions or geographical barriers to gene flow. The phylogenetic reconstruction of the four haplogroups suggests the signatures of glacial refugia and postglacial expansion. The comparison with present-day O. edulis populations revealed a temporally stable population genetic pattern over the past 150 years despite large-scale translocations. This historical phylogeographic reconstruction was able to discover an autochthonous population in the German and Danish Wadden Sea in the late nineteenth century, where O. edulis is extinct today. The genetic distinctiveness of a now-extinct population hints at a connection between the genetic background of O. edulis in the Wadden Sea and for its absence until today

Towards a barnacle tree of life:integrating diverse phylogenetic efforts into a comprehensive hypothesis of thecostracan evolution

Barnacles and their allies (Thecostraca) are a biologically diverse, monophyletic crustacean group, which includes both intensely studied taxa, such as the acorn and stalked barnacles, as well as cryptic taxa, for example, Facetotecta. Recent efforts have clarified phylogenetic relationships in many different parts of the barnacle tree, but the outcomes of these phylogenetic studies have not yet been combined into a single hypothesis for all barnacles. In the present study, we applied a new “synthesis” tree approach to estimate the first working Barnacle Tree of Life. Using this approach, we integrated phylogenetic hypotheses from 27 studies, which did not necessarily include the same taxa or used the same characters, with hierarchical taxonomic information for all recognized species. This first synthesis tree contains 2,070 barnacle species and subspecies, including 239 barnacle species with phylogenetic information and 198 undescribed or unidentified species. The tree had 442 bifurcating nodes, indicating that 79.3% of all nodes are still unresolved. We found that the acorn and stalked barnacles, the Thoracica, and the parasitic Rhizocephala have the largest amount of published phylogenetic information. About half of the thecostracan families for which phylogenetic information was available were polyphyletic. We queried publicly available geographic occurrence databases for the group, gaining a sense of geographic gaps and hotspots in our phylogenetic knowledge. Phylogenetic information is especially lacking for deep sea and Arctic taxa, but even coastal species are not fully incorporated into phylogenetic studies.publishedVersio

Morphological measurements

Morphological measurements (in mm) and collecting information of barnacles from the East coast of the USA and Gulf of Mexico used in the morphological analyses<br

Microsatellite alleles and collecting information

The dataset contains allele calls for all individuals used in the analyses, and associated collecting information<div><br>Microsatellite loci names are Ctest7, Ctest9, Ctest10, Ctest11, Ctest12, Ctest16, Ctest18, Ctest31, Ctest 32, Ctest36, Ctest47<div><br></div><div>Microsatellite allele calls are diploid. Each allele is denoted by three digits, and both alleles are in the same cell, without separator. The numbers represent the DNA fragment length</div></div

Second gonopods of Calappa nitida (USNM 103446)

SEM images of second gonopods of Calappa nitida (USNM 103446). A: overview (note the terminal joint), B: tip with spine

Second gonopods of Calappa granulata (ZMK 1280)

SEM images of second gonopods of Calappa granulata (ZMK 1280). A: overview, B: middle section with terminal joint,v C: tip, D: close-up of ti

Second gonopods of Calappula tortugae (SERTC 300)

SEM images of second gonopods of Calappula tortugae (SERTC 300). A-C: tip from different angles, D-E: middle section with terminal joint from different angle

Second gonopods of Calappa japonica (ZMS 22941)

SEM images of second gonopods of Calappa japonica (ZMS 22941). A: overview (note that gonopod shape is distorted due to faulty drying technique), B: overview of second gonpod prior to drying, C: tip, D: middle section with terminal junctio

Morphological measurements

Morphological measurements (in mm) and collecting information of barnacles from the East coast of the USA and Gulf of Mexico used in the morphological analyses<br