Abstract
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.
Highlights
Steady increases in the demand of certain metals such as nickel, copper and cobalt during the last decade are raising the interest of exploring alternative mining sites like marine mineral deposits [1]
This study was conducted in the high seas in areas beyond national jurisdiction (i.e. the Area in UNCLOS (United Nations Convention on the Law of the Sea) terminology), which are managed by the United Nations International Seabed Authority (ISA)
From the 1900 specimens analyzed, Cytochrome Oxidase Subunit 1 (COI) amplification and sequencing was successful for 556 polychaete and 150 isopod specimens, i.e. 44% and 31% of the total number of polychaetes and isopods selected for genetic analyses, respectively (Table 1)
Summary
Steady increases in the demand of certain metals such as nickel, copper and cobalt during the last decade are raising the interest of exploring alternative mining sites like marine mineral deposits [1]. One type of deposit likely to be mined in the future is formed by polymetallic nodules, as they contain a relatively high proportion of these desirable metals [2,3]. The distribution, size and metal content of polymetallic nodules is determined by a variety of factors which include the degree of oxidation of the environment, the presence of nucleating agents and/or the nature and age of substrate, the proximity of sources of elements [7], sedimentation rates (which are largely influenced by the proximity to sources of sediment supply, overlying productivity and bottom current activity) and the influence of organisms [6,7,8]. Low sedimentation rates (0.3–0.5 cm/1000 y) correlate with high concentrations of nodules at the sediment surface, the highest nodule concentrations are usually found in red clay or siliceous areas [3]
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