A benthic classification system to aid in the implementation of marine protected area networks in the deep/high seas of the NE Atlantic

Internationally there is political momentum to establish networks of representative marine protected areas for the conservation of biodiversity. Mapping the distributions of all species, to ensure representation is achieved within a given network, is not possible. Thus surrogates are frequently used in mapping efforts as measures of biological diversity. For practical purposes these surrogates are often organised into a classification system. A number of classifications systems have been developed that are applicable to the deep-sea. However the biological relevance of both the surrogates used and the divisions or classes defined within each surrogate are often unknown or merely assumed. This study discusses the biological relevance of the five most commonly used surrogates (biogeography, depth, geomorphology, substrate, biological assemblages) to the deep-sea fauna. For each surrogate an extensive literature review of benthic faunal studies from the region is used to construct categories within that surrogate that represent the principal known variation in the faunal composition. A hierarchical classification system is described based on four surrogates that are useful at progressively finer spatial scales: biogeography, depth, substrate, biological assemblages. Geomorphological surrogates, although acknowledged as both useful and relevant in deep-sea work, are omitted as the link between geomorphology and biology needs clarification. Descriptions of 40 benthic megafaunal assemblages are provided as an appendix.