MBDP-NI: Priority habitat

Intertidal Chalk

Intertidal Chalk

Correspondence with existing habitats

Part of 1994 UK BAP habitat: Littoral and sublittoral chalk

OSPAR Habitat: Littoral Chalk Communities

Habitats Directive Annex I: Submerged or partially submerged caves

Habitats Directive Annex I: Reefs

Description: Northern Ireland’s chalk is represented by Cretaceous hard chalk, also known as White Limestone. Chalk rock is mostly found along the Antrim coast and good examples of intertidal chalk can be found at Ballintoy and also on the south side of Rathlin Island.

The erosion of chalk exposures on the coast has resulted in the formation of vertical cliffs and gently-sloping intertidal platforms with a range of micro-habitats of biological importance. The lower littoral fringe may be characterised by a dense mat of green algae Enteromorpha spp. and Ulva lactuca. The low shore can have a characteristic flora and fauna of ‘rock-boring’ invertebrates such as piddocks, overlain by mostly algal-dominated communities (fucoids and red algal turfs) (Gubbay, 2002).

At Rinagree, Portrush the purple sea urchin Paracentrotus lividus is found excavating circular depressions in rockpools in the mid to low eulittoral. The rockpools have a covering of encrusting coralline algae.

Associated biotopes:

Priority species: Edwardsiella carnea

Threats:

Coastal protection works are the main threat to littoral chalk communities, and have led to the loss of micro-habitats on the upper shore and the removal of splash-zone communities, including the unique algal communities (Anon, 2000; Fletcher, 1974; Fowler & Tittley, 1993; Wood & Wood, 1986).
The deterioration of water quality by pollutants and nutrients has caused respectively the replacement of fucoid dominated biotopes by mussel-dominated biotopes, and the occurrence of nuisance Enteromorpha spp. blooms (Anon, 2000; Fletcher, 1974; Fowler & Tittley, 1993; Wood & Wood, 1986).
The human disturbance especially by trampling or stone-turning can lead to physical loss of habitat.
Chalk exposures are vulnerable to oil spills.
Non-natives: Non-native species such as Sargassum muticum have spread all along the coasts of Northern Ireland where they compete with native species. The non-native Pacific oyster Magallana gigas is rapidly spreading around the coasts of Northern Ireland and has the potential to seriously impact this habitat. Non-native species could replace our native species.

References:

Anon (2000) UK Biodiversity Group Tranche 2 Action Plans. Volume V – maritime species and habitats. English Nature, Northminster House PE1 1UA. ISBN 1 85716 467 9. 242 pp.
Doody, J.P., Johnston, C. & Smith, B. (1991). Directory of the North Sea Coastal Margin. Coastal Conservation Branch, Joint Nature Conservation Committee, Peterborough. 419 pp.
Duperret, A., Genter, A., Mortimore, R.N., Lawrence, J.A. & Martinez, A. (2001) A classification of chalk cliff failures, based on recent cliff collapses along the Channel coasts of England and France. Abstract. International Conference on coastal rock slope instability – geohazard and risk analysis. Le Havre, 30-31 May, 2001.
Fletcher, R.L. (1974) Ulva problem in Kent. Mar.Poll.Bull. 5, 21. Fowler, S.L. & Tittley, I. (1993) The marine nature conservation importance of British coastal chalk cliff habitats. English Nature Research Report No.32. English Nature, Peterborough. ICES (2002) Report of the Working Group on Ecosystem Effects of Fisheries. Advisory Committee on Ecosystems. ICES CM 2002/ACE:03.
Wood, E.M. & Wood, C.M. (1986) Channel Tunnel sublittoral survey. Report to the Nature Conservancy Council. Marine Conservation Society, Ross-on-Wye. OSPAR Commission (2008) Case Reports for the OSPAR List of Threatened and/or Declining Species and Habitats.

Marine Biodiversity Data Portal - NI

Intertidal Chalk