Heightened interest in the exploitation of deep seafloor minerals is raising questions on the consequences for the resident fauna. Assessing species ranges and determination of processes underlying current species distributions are prerequisites to conservation planning and predicting faunal responses to changing environmental conditions. The abyssal central Pacific nodule belt, located between the Clarion and Clipperton Fracture Zones (CCZ), is an area prospected for mining of polymetallic nodules. We examined variations in genetic diversity and broad-scale connectivity of isopods and polychaetes across the CCZ. Faunal assemblages were studied from two mining claims (the eastern German and French license areas) located 1300 km apart and influenced by different productivity regimes. Using a reverse taxonomy approach based on DNA barcoding, we tested to what extent distance and large-scale changes in environmental parameters lead to differentiation in two macrofaunal taxa exhibiting different functions and life-history patterns. A fragment of the mitochondrial gene Cytochrome Oxidase Subunit 1 (COI) was analyzed. At a 97% threshold the molecular operational taxonomic units (MOTUs) corresponded well to morphological species. Molecular analyses indicated high local and regional diversity mostly because of large numbers of singletons in the samples. Consequently, variation in composition of genotypic clusters between sites was exceedingly large partly due to paucity of deep-sea sampling and faunal patchiness. A higher proportion of wide-ranging species in polychaetes was contrasted with mostly restricted distributions in isopods. Remarkably, several cryptic lineages appeared to be sympatric and occurred in taxa with putatively good dispersal abilities, whereas some brooding lineages revealed broad distributions across the CCZ. Geographic distance could explain variation in faunal connectivity between regions and sites to some extent, while assumed dispersal capabilities were not as important.
The 3PP marine cave near Marseille (NW Mediterranean) is at a depth of only 15 m. Nevertheless, the cave is a unique deep-sea-like habitat zone due to total darkness, lack of water circulation, oligotrophy, and cold homothermy, a thermal regime similar to that of the deep Mediterranean. We studied the meiofaunal community composition and diversity at 3 sampling stations in the cave (entrance, middle, and blind end). Major taxon composition, based on presence/absence data, did not vary over the transect; however, significant differences in community were found. Tardigrades were the only major taxon restricted to the inner parts of the cave. Copepod diversity decreased towards the inner parts of the cave. The 3PP Cave was characterized by very low abundances of meiofaunal organisms similar to abyssal sites elsewhere. A total of 405 individual copepods were assigned to 27 families and 90 species (75% of them new to science). Significant differences in copepod communities between stations were found at family, genus, and species level. Some harpacticoid taxa generally known from the deep sea, such as Marsteinia, Ancorabolina, Paranannopus, Nematovorax, and Argestidae, were represented in the 3PP Cave. A naive Bayes model was used for the first time to classify the communities as 'shallow' or 'abyssal'. The meiobenthic communities at the entrance and the end of the cave were unequi vocally classified as 'shallow' and 'abyssal' respectively, while the middle part of the cave presented a mixed community. Our study further highlights the strong faunal and community affinities between marine caves and the deep sea, indicating the existence of dispersal mechanisms from deep waters into the euphotic zone for benthic organisms
Spatial patterns of genetic variation (based on COI and 16S mtDNA) for morphologically similar species in the isopod genus Nannoniscus G.O. Sars. 1870 were examined that occur broadly across the Clarion Clipperton Fracture Zone (CCZ). Samples were obtained from five different licence areas as well as an Area of Particular Environmental Interest (APEI-6) with sites located at various distances (a few to several hundred kilometres) from one another. Applying three different species delimitation (SD) methods (sGMYC, mPTP and ABGD) of the molecular data, we could distinguish between four and 12 different molecular taxonomic operational units (MOTUs). Morphological analyses could confirm five distinct phenotypic clades that represent species new to science and are described here: Nannoniscus brenkei sp. nov., Nannoniscus hilario sp. nov., Nannoniscus magdae sp. nov., Nannoniscus menoti sp. nov. and Nannoniscus pedro sp. nov. Despite the assumed limited dispersal capacity of Nannoniscus species, we found haplotypes of two species to be geographically widespread (up to > 1400 km apart), as opposed to several divergent clades occurring in close vicinity or even sympatry. Geographic distance appeared to explain the phylogeographic structure of Nannoniscus species to some extent, although oceanographic features and level of environmental heterogeneity were probably equally important.
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