Faunal biogeography, community structure, and genetic connectivity of North Atlantic seamounts

Abstract

The mechanisms of faunal dispersal across ocean basins are key unknowns toward understanding of the modern biogeography and biodiversity of deep-sea fauna. Seamounts are considered to play a defining role in faunal evolution, acting as regional centers of speciation, “stepping-stones” for dispersal, and/or refugia for deep-sea populations. The overarching goal of this dissertation was to examine the role of seamounts in structuring marine biodiversity and biogeography. This study focused on North Atlantic seamounts, specifically the New England seamount chain, the Corner Rise seamounts, and Muir seamount, areas damaged and threatened by deep-sea fisheries and currently a focus of conservation efforts. Videographic analyses of biological community structure revealed distinct faunal assemblages, dominated by the Porifera, Cnidaria, and Echinodermata and structured by geographic region, depth regions (with apparent taxonomic breaks at 1300 m, 2300 m, and 2600 m), and substrate type (including natural/anthropogenic and abiotic substrates and biotic substrates). Amongst these assemblages, seven highly specific coral host- invertebrate associate relationships were identified. To investigate whether or not these broad community patterns were discernible at a genetic level, the 16S mtDNA gene was utilized as a genetic “barcode” within the Class Ophiuroidea, through which 22 putative species were identified, including four target species (Asteroschema clavigera, Ophiocreas oedipus, Ophioplinthaca abyssalis, and Ophioplinthaca chelys) for subsequent population genetic studies. Analyses of mitochondrial 16S and COI gene sequences revealed evidence for recent population expansion and estimates of recent high gene flow across all four species throughout the North Atlantic seamount region. However, genetic differentiation within populations of A. clavigera and O. chelys within seamount regions was significant, suggesting that historical diversification has been mediated by a long-distance dispersal mechanism that homogenizes this genetic signal on a regional scale. In addition, comparisons of all ophiuroid populations revealed no congruent pattern of historical migration amongst seamounts, which may also be attributed to the varying levels of host specificity and reproductive strategy of each ophiuroid species. These results will guide future studies and conservation efforts to protect seamount communities vulnerable to deep-sea fishery activities.