Littoral chalk communities

Special communities of animals and seaweeds that live on chalk seashores

Littoral chalk communities © Lin Baldock

Chalk is a soft, pure limestone and is easily eroded by seawater.  This results in a characteristic type of beach, with a wide shore, often extending for many hundreds of metres, backed by vertical cliffs.

Above the high water mark, where the chalk cliffs and sea caves are splashed by waves, there are unique communities of seaweeds.  These appear as orange, brown or black slimy bands on the white chalk. Slightly lower down the shore, where they are covered regularly by the tide, dense mats of green seaweeds, such as gutweed and sea lettuce, may occur.  Closer to the low water mark, ‘rock-boring’ animals such as piddocks (elongated bivalves, with paired halves to their shells) are found.  Seaweeds, and the animal communities that associate with them, overlie these.

Human impacts on these habitats include coastal protection works. This has a greater effect on the chalk at higher levels on the shore.  Large port and harbour developments can have major impacts on the lower shore and shallow waters. 

Chalk communities on the shore are vulnerable to pollution and oil spills, and habitat is lost through human disturbance - trampling, stone-turning, small-scale fisheries.  Native species have been displaced by the invasion of non-native plants.  These ‘aliens’ include the Japanese seaweed ‘japweed’, which was accidentally introduced to the Solent in the 1970s, and has subsequently spread all along the south coast of England and beyond. 

Chalk communities are scarce, and so any impacts have a significant effect.

For the official habitat definition please see the documents listed below.

 

European distribution

Such coastal exposures of chalk are rare in Europe: over half of these seascapes are recorded from the southern and eastern coasts of England, although they do also occur in France, Denmark and Germany.

 

Conservation status/need

Littoral chalk communities fact

  • This is a UK BAP Priority Habitat (BAP habitats are now Habitats of Principal Importance/Priority Habitats).
  • OSPAR List of Threatened and/or Declining Species and Habitats (Region II – Greater North Sea)
  • Annex I of the Habitats Directive: Submerged or partially submerged caves & Reefs

 

Official definition

UK Biodiversity Action Plan; Priority Habitat Descriptions. BRIG (ed. Ant Maddock) 2008 (updated December 2011)

Descriptions of habitats on the OSPAR list of threatened and/or declining species and habitats (OSPAR agreement 2008/07).

 

Further information

OSPAR Commission - Background Document for Littoral chalk communities

JNCC - UK BAP Priority Species and Habitats

Kent BAP

JNCC EUNIS habitat correlations table