Intertidal Chalk

The erosion of chalk along the coast has resulted in the formation of vertical cliffs and gently-sloping intertidal platforms. These platforms often extend for hundreds of metres and show a range of plant and animal communities associated with each level of the intertidal area. Above the high water mark, chalk cliffs and sea caves support communities of algae. Moving towards the sea, dense mats of green algae form, with ‘rock-boring’ invertebrates found lower down the shore.

intertidal chalk

Photo: Peter Wakely/Natural England

Why is it important?

  • Marine chalk communities are scarce as the features can only form in the right kind of geology.
  • Communities are often unique to this habitat, for example the algae found where chalk cliffs and sea caves are splashed by waves.
  • Erosion of chalk can provide a diverse range of microhabitats such as wave-cut platforms, rock outcrops and large boulders.

Intertidal Chalk in Sussex

Coastal exposures of chalk are rare and over half of these seascapes are recorded from the southern and eastern coasts of England. The area between Brighton and Eastbourne has considerable expanses of intertidal chalk.

What are the threats?

  • Coastal protection works and large developments are the main threat and surveys have estimated that 33% of coastal chalk in Sussex has been modified by coastal defence and other works
  • Pollution including nutrients can change community composition and lead to algal blooms
  • Disturbance such as trampling and stone-turning can cause physical loss and damage
  • Invasion of non-native plants such as Wireweed Sargassum muticum displaces native species

Some associated species

  • Tompot Blenny Parablennius gattorugine
  • a bristleworm Polydora ciliate
  • White Piddock Barnea candida
  • Gutweed Ulva intestinalis
  • Sea lettuce Ulva lactuca

Blue-rayed Limpet on kelp

Photo: Paul Naylor/Sussex Wildlife Trust

Links to more information

The Marine Life Information Network