Marine Biodiversity Data Portal - NI

Correspondence with existing habitats

OSPAR habitat: Sea-pen and burrowing megafauna communities

Habitats Directive Annex I: Large shallow inlets and bays

Description: Mud habitats in deep water (circalittoral muds) usually occur below 20 - 30 m. The relatively stable conditions associated with deep mud habitats often lead to the establishment of communities of burrowing megafaunal species where bathyal species may occur with coastal species. The burrowing megafaunal species include burrowing crustaceans such as Nephrops norvegicus and Callianassa subterranea.

The mud habitats in deep water can also support populations of slender seapen Virgularia mirabilis and the brittlestars Amphiura spp. Burrows and mounds produced by megafauna are prominent features on the surface of plains of fine mud, amongst conspicuous populations of seapens.

These soft mud communities occur at sites that are typically sheltered from wave action, and may occur in quite shallow depths (around 15m). These communities also occur in deep offshore waters in the Irish Sea. Other burrowing crustaceans include Calocaris macandreae, C. subterranea and Goneplax rhomboides. Epibenthic scavengers include Asterias rubens, Pagurus bernhardus and Polybius depurator. Brittlestars may be present and the infauna can contain populations of polychaetes and bivalves.

Associated biotopes:

• SS.SMu.CSaMu – Circalittoral sandy mud
• SS.SMu.CFiMu – Circalittoral fine mud
• SS.SMu.OMu – Offshore circalittoral mud

• EUNIS code: A5.35, A5.36 and A5.37

  Particular attention focuses on the sub-biotopes that contain important biological communities:

• SS.SMu.CFiMu.SpnMeg – Seapens and burrowing megafauna in circalittoral fine mud

• EUNIS code: A5.361

Priority species: Anemonactis mazeli, Labidoplax media, Leptosynapta bergensis

Threats:

• Demersal fishing: principally for Nephrops norvegicus. Nephrops is one of the most important fisheries in Northern Ireland and benthic trawls or pots/creels are the two methods of fishing employed. The use of benthic trawls can result in the removal of non-target species and disturbance to the seabed. Potting for prawns and other crustaceans, selectively removes some of the burrowing megafauna from deep mud.
• Fish farms: may have direct effects on mud communities, including smothering and increasing the biological oxygen demand of the mud. Additional effects may result from the discharges of chemicals, some of which are especially toxic to crustaceans.
• Pollution: Nutrient enrichment leading to eutrophication can have significant detrimental effects. This can lead to changes in the structure and composition of deep mud communities.
• Development: The construction of roads, bridges and barrages may affect the local hydrodynamic and sediment transport regimes of inshore enclosed areas and consequently affect the deep mud substratum.
• Anchoring: This can cause physical damage to sessile megafaunal species such as the seapen Virgularia mirabilis.
• Offshore installations: These can cause a variety of disturbance effects such as smothering and localised disturbance of sediments due to anchoring and installation.

References:

This habitat description has been adapted from the 1994 UK BAP Action Plan for Mud habitats in deep water.