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We examine the main drivers that may elevate biomass and biodiversity of non-chemosynthetic benthic megafauna of the lower bathyal (800-3500m depth) of the Mid-Atlantic Ridge in the North Atlantic Ocean (MAR). Specifically: 1. Primary production in surface waters (10°-48°N) from remote sensing data 2002-2020 over the MAR was not significantly different from abyssal regions to the east and west. We reject the hypothesis that presence of a mid ocean ridge may enhance surface primary production. 2. The quantity of particulate organic matter reaching the sea floor was estimated as a proportion of surface export production scaled by bathymetry. Flux was 1.3 to 3.0 times greater on the MAR as a function of shorter vertical transport distance from the surface than on adjacent abyssal regions. 3. Depth variation effect on species richness. Demersal fishes living between 41° and 60°N showed a maximum of species richness at 2000 m depth and linear increase in regional (Gamma) diversity of 32 species per 1,000 m elevation of the MAR above the abyss. Elevated topography provides niches for species that cannot otherwise survive. 4. Substrate heterogeneity. The MAR >95% covered with soft sediment with frequent hard rocky patches spaced at a mean nearest neighbour distance of

Abstract: To assess the impact and fate of the summer phytoplankton bloom on Antarctic benthos, we evaluated temporal and spatial patterns in macrofaunal abundance and taxonomic composition along a transect crossing the West Antarctic Peninsula (WAP) continental shelf. As part of the FOODBANCS project, we sampled three sites at 550–625m depths during five cruises occurring in November 1999, February–March 2000, June 2000, October 2000 and March 2001. We used a combination of megacore and box-core samplers to take 81 samples, and collected over 30,000 macrofaunal individuals, one of the largest sampling efforts on the Antarctic shelf to date. Comparison of the two sampling methodologies (box core and megacore) indicates similar macrofaunal densities, but with significant differences in taxonomic composition, a reflection of the different spatial scales of sampling. Macrofaunal abundances on the WAP shelf were relatively high compared to other Antarctic shelf settings. At two of the three sampling sites, macrofaunal abundance remained constant throughout the year, which is consistent with the presence of a sediment ‘food bank’. Differences were observed in taxonomic composition at the site closest to the coast (Station A), driven by higher abundances of sub-surface-deposit feeders. A significant temporal response was observed in the ampharetid polychaetes at Station A, with an abundance peak in the late fall post-bloom period; this may have resulted from juvenile recruitment during the summer bloom. Familial composition of macrofaunal polychaetes on the WAP shelf is more closely related to deep-sea abyssal fauna than to other shelf regions, and we hypothesize that this is a result of both local ecological conditions (low temperatures) and a reflection of historical processes such as extinctions on the Antarctic shelf during previous glacial maxima followed by recolonization from the deep sea. [Copyright &y& Elsevier]