evidence: The Hatton-Rockall Basin MPA is situated in a deep-water basin to the far west of Scotland. Water depth at the site is over 1 km and the muddy sediments present support a range of species adapted to life at this depth. [...] The Hatton-Rockall Basin MPA is situated in a deep-water basin to the far west of Scotland. The site is located between Hatton Bank to the west and Rockall Bank to the east and water depth at the site is over 1 km. The site is designated to protect unusual aggregations of deep-sea sponges, an OSPAR Threatened and/or Declining habitat. Two different types of deep-sea sponge aggregations are known to be present; aggregations dominated by encrusting sponges and bird’s nest sponge (Pheronema carpenteri) fields. The bird’s nest sponge fields within the site are the only known examples to occur in UK waters. The encrusting sponge aggregation is typified by encrusting grey sponges living on boulders and mud substrata. Both types of deep-sea sponge aggregations act as biodiversity hotspots, with a range of other species associated with them. For the bird’s nest sponge fields, these include ascidians, formaniferans, polychaetes and burrowing anemones, while the encrusting sponge aggregations include anemones, ascidians, crinoids and ophiuroids. The seabed in the area is littered with spicules, spiny remnants of dead sponges, that inhibit the establishment of burrowing animals but allow surface-dwelling species to thrive.