Dynamics of Near-Bottom Currents in Cold-Water Coral and Sponge Areas along the Walvis Ridge.

Cold-water corals and sponges form iconic and globally occurring benthic communities, provide important habitats for a diverse associated fauna and thrive in environmental conditions with often large temporal and spatial variations in near-bottom currents, food availability and other environmental parameters. We investigate the variability of near‐bottom currents and physical processes from simulations with a nested hydrodynamic modelling framework at two seamounts rich in benthic fauna along the Northeast Walvis Ridge, Valdivia Bank and Ewing Seamount. Our aim is to obtain new insights on physical drivers of observed occurrences and distribution of benthic suspension feeders (cnidarians and sponges) in this data‐poor area. We use dynamic downscaling of high-resolution implementations of the ROMS-AGRIF model in combination with high-resolution bathymetry and open boundary forcing from the basin-scale model INALT20 and the OSU inverse tidal model to explore the fine-scale physical processes and mechanisms that potentially drive a continuous or episodic food supply to the benthic communities.  Over a three-year period, we analysed how near-bottom currents vary in space and time and assess potential connections between the distribution of filter-feeding fauna and the surrounding physical marine environment. We identified a close link between flow dynamics, internal tide dynamics and faunal species distributions. We propose that physical processes such as kinetic energy dissipation and internal wave dynamics could serve as functional indicators of food supply and particle encounter rates in future species distribution and habitat suitability models for important deep-sea taxa, such as those that represent vulnerable marine ecosystems. Our results also show little impact of mesoscale eddies from the Agulhas Leakage as they propagate north-westward into the southeast Atlantic along a well-defined corridor, which only occasionally extends as far north as the Valdivia Bank and Ewing Seamount.