The seabed of the Celtic Seas ecoregion is primarily comprised of sediments (Figure 13). Coarse sediments cover most of the Malin Shelf. Coarse sediments are also the main substrate type found in the Irish Sea along with patches of mud to muddy sand and rock, sandbanks are prominent features off the southeast coast of Ireland. Coarse sediment, sand and mud to muddy sands are found in equal measures in the Celtic Sea. Areas of rock and hard substratum are present in the northern (west of Shetland Islands) and inshore (west and south coasts of Ireland, south west England coastline) parts of the ecoregion. Mud to muddy sand sediments dominate the deeper, offshore areas.
The soft sediments are characterized by burrowing megafauna; this includes sea pens and commercially important species (e.g. Norway lobster [Nephrops norvegicus]), and also macrobenthos such as deposit-feeding polychaetes. The coarser sediments are habitats for commercially important shellfish species, e.g. Pecten maximus and Aequipecten opercularis, and to sensitive species and habitats, e.g. maerl, brittle star beds, Modiolus modiolus beds, and Atrina fragilis. The nearshore rocky habitats are characterized by algae and epifauna; however, some areas of rocky habitat in deep waters in the northern part of the region are characterized by hydroids, bryozoans, and cnidarians such as Eunicella verrucosa and Swiftia pallida. Structural changes in benthic communities and declines in native species have been observed as a result of the more than 200 non-indigenous and cryptogenic (unknown origin) species recorded in the region as a result of shipping, coastal water currents, and aquaculture.
Vulnerable marine ecosystems (VMEs)
There are 3091 records of VME habitats and 9278 records of VME indicator taxa in the Celtic Seas ecoregion below 200 m in depth. VMEs in regions shallower than 200 m may exist but are not recorded in the VME database. All records for the VME habitats come from the northwest of Scotland, west of Ireland, and the Celtic Sea while no records have been made for the Malin Shelf and the Irish Sea. However, a small portion of VME indicator records do arise from the Malin Shelf and the Irish Sea.
VME habitats include anemone aggregations, cold-water coral reefs, coral gardens, deep-sea sponge aggregations, sea pen fields, stalked crinoid aggregations, tube-dwelling anemone aggregations, and xenophyophore aggregations. VME indicator taxa recorded are: anemones, black corals, cup corals, gorgonians, sea pens, soft coral, sponges, stony corals, stylasterids (lace corals), and xenophyophores.
OSPAR threatened and/or declining habitats
Additional recorded occurrences (i.e. <200 m depth) of Sabellaria spinulosa reefs in the ecoregion are concentrated around the west coasts of England and Wales with a more scattered distribution around Scotland and Ireland (Figure 9). Modiolus modiolus beds occur patchily in the Irish Sea.