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Unveiling ophiuroid biodiversity across North Atlantic habitats via an integrative perspective.
Schmidt LA
,
Brix S
,
Rossel S
,
Forster S
,
Eichsteller A
.
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The depths of the North Atlantic Ocean host a species-rich fauna providing heterogeneous habitats from thermal vent fields to cold-water coral reefs. With the increasing threat of destruction of deep-sea habitats due to human impacts, such as demersal fishing and the beginning of deep-sea mining, an analysis of the diversity and distribution of species is crucial for conservation efforts. Brittle stars occur in high biomasses, contributing to the biodiversity of the seafloor. Specimens were collected during several scientific expeditions to gain a more detailed insight into the brittle star diversity in the North Atlantic Ocean. An integrative approach to identify the species with DNA barcoding (mtCOI) in combination with morphological studies revealed 24 species. Most species have been previously identified in the North Atlantic, but sequences for 13 species are newly added to public repositories. Additionally, the MALDI-TOF-MS proteomic analysis was successfully applied for 197 specimens with known COI barcodes. Results are congruent with other molecular species delimitations demonstrating the functionality of proteomics for the identification of brittle stars. This dataset significantly expands our understanding of the taxonomic and genetic diversity of brittle stars and contributes to publicly available data. It emphasizes the importance of considering habitat heterogeneity for large scale patterns of biodiversity.
Fig. 1. Bathymetric map of the sampling stations during the cruises IceDivA (SO280), IceDivA 2 (SO286), and IceAGE 3 (SO276). Each point represents one sampling area. The numbers represent the area where the stations are located (1) Aegir Ridge (2) Iceland-Faroe Ridge (3) Lóndsjúp (4) Vent field (5) NACES MPA (6) Abyssal plain 49N (7) Abyssal plain 41N (8) Azores south (9) Abyssal plain 36N. The symbol represents the cruise while the color indicates the sampled habitat. Map created in QGIS Version 3.32 (https://lima.qgis.org).
Fig. 2. Exemplary illustration of the seabed characteristics within each habitat category: (A) Seamount base25 (B) Cold-water coral reef (SO276)26 (C) Ocean ridge (SO276)26 (D) Deep seafloor (SO286)25, (E) Abyssal plain (SO276)26. (F) Vent field (SO276)26.
Fig. 4. Ultrametric BI tree with the applied GMYC model of 219 mtCOI sequences from North Atlantic and Arctic brittle stars. The mtCOI fragment with a length of 658 bp and the additional GenBank sequences (see Supplementary Table S1) were computed with a strict clock model and an MCMC chain length of 10,000,000. The colored vertical bars represent the results of the applied species delimitation methods (GMYC, ABGD (prior maximal distance P = 0.0215) and the BIN system). The species to which the sequences are assigned is marked on the right with the associated families highlighted to the left. The sequences downloaded from GenBank are marked with a gray line.
Fig. 5. MALDI-TOF MS analyses. (a) Hierarchical clustering based on 197 protein mass spectra. Colors indicate species affiliations of collapsed clusters. Except for a single O. arcticus specimen, all specimens cluster according to their morphological and genetic identification. (b) TSNE plot resulting from a RF model including all species with at least three specimens. None of the specimens, including the single O. arcticus, was misclassified within the RF model indicating its usability in a classification approach.
Fig. 6. Distribution of the different species according to the various sampling areas and habitats, along with a visualization of the brittle star species composition in the classified habitats. Species are represented by specific colors and symbols, which are consistent across both subfigures for clarity. (a) The six habitats are indicated on the map with the associated color shown in the legend. The species occurring at a site are indicated in the circles associated with the respective sites by their color and symbol. Map created in QGIS Version 3.32. (b) For each habitat, the total number of barcoded specimens is shown, and the associated species is represented by the different colors of the bars. The total number of species is shown with gray numbers.
