Cold-water coral distributions and surficial geology at five spatial scales on the Flemish Cap, northwest Atlantic

Abstract

Cold-water coral (CWC) distributions are strongly influenced by substrate, as they are sessile, long-lived benthic species. While the attachment substrate preferences (hard vs. soft) of many coral species are well known, the relationships between coral species distributions and geological environments are less clear. This study investigates the relationship between CWC distribution and geological environments in a deep offshore setting, examining both surficial geology and bedrock lithology. In 2010 we used a remotely operated vehicle to conduct four video surveys on the southern and eastern flanks of the Flemish Cap, NW Atlantic, ranging in depths from 870 m to 2900 m. CWC were identified to the lowest possible taxonomic level and assigned to functional groups: large gorgonians, small gorgonians, soft corals, pennatulaceans, antipatharians, Desmophyllum dianthus, and reclining solitary scleractinians. Surficial geology was classified at five spatial scales (10 m, 50 m, 100 m, 500 m, 1000 m) along each transect into one of six surficial geological and/or lithological geological facies (fine grained sediment, gravelly fine grained sediment, fine grained sediment and bedrock, igneous bedrock, and sedimentary bedrock). A total of thirty CWC species were observed, with each transect displaying a unique species composition and surficial geology. Functional groups were represented on most facies and depths. Anthomastus sp. (soft coral) was the most abundant coral species observed, and was found on most facies and depths. Soft corals and large gorgonians were the most abundant on the gravelly fine grain and sedimentary bedrock facies between 1673-1873 m. Analysis of Similarity (ANOSIM) showed an influence of both facies and depth on coral species composition, with depth apparently more important. Geological facies had a significant difference on coral species composition when measured at finer scales (10 m, 50 m, 100 m, and 500 m) but not at broader scales (1000m). Of the fine scales, 100 m was the most significant for both CWC species and functional groups. Our results suggest that bathymetry and oceanography are dominant influences on coral distribution at broad scales, with surficial geology dominating distributions at scales finer than 1 km.