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Members of the sea anemone genus Metridium are abundant in temperate rocky habitats and fouling communities. Their biogeographic history is expected to reflect changes in currents and habitats that have influenced benthic communities, such as the climate-influenced changes that occurred during the Last Glacial Maximum. More recently, however, anthropogenic influences such as shipping transportation and the creation of artificial habitat have altered and affected the composition of modern-day marine communities. Here we use sequence-capture data to examine the genetic structure of Metridium across its shallow-water distribution to (1) evaluate species boundaries within Metridium , (2) elucidate the dispersal history of Metridium between and among oceans, and (3) assess the influence of anthropogenic movement on modern-day populations. We find strong evidence for two species within Metridium : M. farcimen and M. senile. Dispersal from the Pacific to the Atlantic included a subsequent isolation of a small population in or above the Bering Sea, which has presumably moved southward. Within the native range of M. senile , admixture is prevalent even between oceans as a result of anthropogenic activities. The nonnative populations in Chile and the Falkland Islands came from at least two distinct introduction events originating from both coasts of the United States in the North Pacific and North Atlantic Oceans. Hybridization between M. senile and M. farcimen is documented as occurring in anthropogenically influenced habitats. The heavy influence from anthropogenic activities will continue to impact our understanding of marine organisms, particularly within the native range and for those that are easily transported across long distances. [ABSTRACT FROM AUTHOR]

The Patagonian toothfish, Dissostichus eleginoides, is one of the largest predatory fishes inhabiting Southern Ocean waters spanning the Antarctic Polar Front (APF), a prominent biogeographic boundary restricting gene flow and driving species divergence between Antarctic and sub‐Antarctic waters. In the light of emerging threats to toothfish conservation and sustainability, this study investigated genetic [mtDNA sequences and genome wide nuclear single nucleotide polymorphisms (SNPs)] and morphological data to critically evaluate the taxonomic status of toothfish north (Chile and Patagonian shelf) and south (South Georgia and South Sandwich Islands) of the APF. mtDNA revealed reciprocally monophyletic lineages on either side of the APF with coalescent analysis indicating these diverged during the Pleistocene. Integration with data from other sources suggests the Chilean/Patagonian lineage is endemic. SNP analysis confirmed restricted nuclear gene flow between both groups and revealed a consensus suite of positive outlier SNPs compatible with adaptive divergence between these groups. Finally, several morphological features permit unequivocal assignment of individuals to either of the clades. Based on the genetic, phenotypic and ecological divergence, the authors propose that toothfish on either side of the APF be recognised as distinct species, with the name D. eleginoides used for toothfish occurring in South American waters north of the APF and toothfish south of the APF being classified using the new name D. australis reflecting their southern distribution. [ABSTRACT FROM AUTHOR]