The Nordic Seas have one of the highest water-mass diversities in the world, yet large knowledge gaps exist in biodiversity structure and biogeographical distribution patterns of the deep macrobenthic fauna. This study focuses on the marine bottom-dwelling peracarid crustacean taxon Cumacea from northern waters, using a combined approach of morphological and molecular techniques to present one of the first insights into genetic variability of this taxon. In total, 947 specimens were assigned to 77 morphologically differing species, representing all seven known families from the North Atlantic. A total of 131 specimens were studied genetically (16S rRNA) and divided into 53 putative species by species delimitation methods (GMYC and ABGD). In most cases, morphological and molecular-genetic delimitation was fully congruent, highlighting the overall success and high quality of both approaches. Differences were due to eight instances resulting in either ecologically driven morphological diversification of species or morphologically cryptic species, uncovering hidden diversity. An interspecific genetic distance of at least 8% was observed with a clear barcoding gap for molecular delimitation of cumacean species. Combining these findings with data from public databases and specimens collected during different international expeditions revealed a change in the composition of taxa from a Northern Atlantic-boreal to an Arctic community. The Greenland-Iceland-Scotland-Ridge (GIS-Ridge) acts as a geographical barrier and/or predominate water masses correspond well with cumacean taxa dominance. A closer investigation on species level revealed occurrences across multiple ecoregions or patchy distributions within defined ecoregions.
In this study, we describe a new species of cladorhizid sponge, which shows a very peculiar mode of life: It always occurs in association with the scleractinian cold-water corals Lophelia pertusa and Madrepora oculata. Although the sponge lives in nutrient-rich areas, we document its carnivorous feeding behavior. The identity of the new species was verified using molecular markers: the species is very closely related to the North-Atlantic Cladorhiza abyssicola, but it differs distinctly, and forms a monophyletic clade. The two species might be considered very close relatives, probably sister species deriving from a common ancestor.
The species Mulinia lateralis (Say, 1822) is native in the western North Atlantic Ocean and was first documented in European coastal waters in 2017. Since then, M. lateralis was reported several times in large abundances in the coastal waters of the Netherlands, Belgium and Germany. While the introduction vector is still unclear we assume that further dispersal in the southern North Sea will be driven by larval drift related to anti-clockwise residual tidal currents. To report its current distribution status in the central Wadden Sea, individuals were collected systematically from intertidal flats along 10 transects ranging from the outer Ems River estuary to the outer Elbe River estuary (German North Sea coast) between February and May 2022. In total, 897 specimens of M. lateralis were sampled from 392 stations (mean abundance 2.29 ± 4.97 ind./m²). The shell length ranged between 3.98 and 23.55 mm thus representing at minimum two cohorts. Regarding the increasing number of records of M. lateralis at multiple sites in Europe since 2017, the species can be considered as established in the western and central Wadden Sea.
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