Abstract
Cold-water corals build up reef structures or coral gardens and play an important role for many organisms in the deep sea. Climate change, deep-sea mining, and bottom trawling are severely compromising these ecosystems, making it all the more important to document the diversity, distribution, and impacts on corals. This goes hand in hand with species identification, which is morphologically and genetically challenging for Hexa- and Octocorallia. Morphological variation and slowly evolving molecular markers both contribute to the difficulty of species identification. In this study, a fast and cheap species delimitation tool for Octocorallia and Scleractinia, an order of the Hexacorallia, of the Northeast Atlantic was tested based on 49 specimens. Two nuclear markers (ITS2 and 28S rDNA) and two mitochondrial markers (COI and mtMutS) were sequenced. The sequences formed the basis of a reference library for comparison to the results of species delimitation based on proteomic fingerprinting using MALDI-TOF MS. The genetic methods were able to distinguish 17 of 18 presumed species. Due to a lack of replicates, using proteome fingerprinting only 7 species were distinguishable. Species that could not be distinguished from one another still achieved good signals of spectra but were not represented by enough specimens for comparison. Therefore, it is predicted that with an extensive reference library of proteome spectra for Scleractinia and Octocorallia, MALDI-TOF MS may provide a rapid and cost-effective alternative for species discrimination in corals.
Highlights
Octocorallia and Scleractinia of the subclass Hexacorallia are two of the major groups of cnidarians with continuous or discontinuous calcium carbonate or horn-like skeletons that are commonly known as corals
In contrast to Scleractinia, the polyps and soft tissues are relatively invariant in Octocorallia, and taxonomic classification has historically been based on the shape of colonies and the morphology of sclerites (Fabricius and Alderslade, 2001)
We examine the coral assemblages around Iceland and compare the discrimination power of genetic and proteomic methods for species identification
Summary
Octocorallia and Scleractinia of the subclass Hexacorallia are two of the major groups of cnidarians with continuous or discontinuous calcium carbonate or horn-like skeletons that are commonly known as corals. Scleractinian classification has traditionally been based on morphological characters of the skeleton, including those that can be assessed in fossil genera (Wells, 1956; Daly et al, 2007). Subsequent integrative taxonomic studies combining morphological and molecular data have identified new microskeletal characters that are congruent with molecular evidence, leading to widespread reinterpretation of species boundaries and recognition of cryptic taxa in many scleractinian genera e.g., (Keshavmurthy et al, 2013; Arrigoni et al, 2016a,b, 2020). The taxonomy of Octocorallia, a group encompassing approximately 3,500 extant species of soft corals, sea pens, and gorgonians, is even less well understood (McFadden et al, 2010). In contrast to Scleractinia, the polyps and soft tissues are relatively invariant in Octocorallia, and taxonomic classification has historically been based on the shape of colonies and the morphology of sclerites (microscopic calcareous skeletal elements) (Fabricius and Alderslade, 2001). Morphological characters congruent with the molecular data have been more difficult to identify in octocorals, with the result that some species can be distinguished by molecular characters alone (e.g., Pante et al, 2015; McFadden et al, 2017)
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