A DNA barcode reference library for the superorder Peracarida (Crustacea) from the Southern European Atlantic coast

Problem statement Peracarida is a Superorder of the subphylum Crustacea and one of the most diverse and widely distributed groups of crustaceans. In marine coasts, peracaridean species are among the most ecologically important invertebrates, with high relevance in trophic interactions and constituting one of the dominant groups and key components of marine benthic communities. The Superorder currently contains more than 18000 known species listed in the World Register of Marine Species (WORMS), but experts claim that numerous species still await formal description. Several orders are included in this group such as Amphipoda, Isopoda, Tanaidacea among others. The peracaridean fauna of the southern Atlantic European coasts is particularly rich and unique, consisting on a mixture of species from adjacent biogeographic regions such as the Mediterranean Sea and the warm and cold temperate Northeast Atlantic. Being a biogeographic cross road region where many percaridean species have their distribution limits, this region is particularly relevant for monitoring alterations in distributional ranges driven by different factors, such as climate change, the introduction of alien species or anthropogenic activities. Although these organisms constitute one of the most diverse groups of crustaceans, they are often neglected in most ecological surveys and have been poorly studied in comparison to other taxa of similar ecological importance. A rigorous and extensive knowledge of the peracaridean biodiversity has not been reached yet, which may compromise the informed planning and management of the marine environment. As with many other marine invertebrate taxa, rigorous species identifications can be rather challenging, with the knowledge of peracaridean diversity being constrained by the taxonomic impediment. In recent years, the use of molecular tools for specimen identification and classification has become quite widespread and it has been used to complement morphological identifications. The use of a standard universal system, like the DNA barcode, a standard region of mitochondrial cytochrome c oxidase gene (COI-5P) with 658 base pair (bp), has been shown to be successful in species classification and delimitation in several marine groups. Furthermore has been contributing to improve the detection of potential new species and to facilitate specimen identification, particularly of cryptic species and other organisms with complex or hardly-accessible morphology. The availability of reliable, scrutinized and annotated reference libraries of DNA barcodes is a fundamental backbone of this DNAbased species identification system. Nevertheless, marine invertebrate species are still poorly represented in the published reference libraries, and only a small fraction of the species occurring in our European marine “backyard” are represented, namely the peracaridean crustaceans (Raupach and Radulovici 2015). In this study we report and examine a core DNA barcode library for the Peracarida from the Southern Atlantic European Coast, focusing on representatives of the orders Amphipoda, Isopoda and Tanaidacea.