The British Isles have extensive and varied coastlines, ranging dramatically between wave beaten rocky shores, sandy beaches, shingle ridges, sheltered coves and cliffs. Unlike rapidly changing sandy shores, rocky shore habitats are relatively stable and provide secure surfaces for living things to attach to and hide within. The wind, waves, and temperature and salinity of the water work together with the animals that live there to shape the shoreline. The typical rock, which makes up a shore will vary, which in turn determines the type of animals, plants and algae that will colonise the area. Soft rocks such as chalk or limestone are easily eroded and may provide a home for animals, which drill holes and live inside the rock. Harder rocks such as granite will have less features such as pools and crevices and no boring animals. To find out more about how animals help to shape the shore, check out the information and resources on our Shore Shapers pages.
Common shore crabs are found on rocky shores around the British Isles. This female is protecting its bright orange eggs
The shore (or intertidal zone) marks the transition between the sea and land, with water moving up and down daily at the rhythm of the tides (which can be different depending on which part of the world you are in). As a result, rocky shores have well defined vertical gradient of animals and plants that have different levels of tolerance to the stresses caused by the tide going in and out. In general, conditions become more stable further down the shore, due to the amount of time under water. However, sunlight increases higher up the shore and competition reduces, meaning that any species adapted to survive the harsh conditions can potentially do very well! The greadient can be simplified by looking at the shore as a series of zones. The main intertidal zones on rocky shore in the British Isles are:
Splash zone – is the area just above the limit of high tide. This zone may be submerged occasionally during storms and high spring tides and is ‘sprayed’ by salty water from the sea. This zone is home to a small number of salt loving plants, lichens and a small number of specially adapted land invertebrates.Channeled Wrack can survive out of the water for several days and is typical of the upper shore
Upper Shore – is the area at the limit of high tide, it is only submerged for a few hours each day and is dominated by small periwinkles, barnacles, limpets and encrusting lichens. Some species of algae such as channeled wrack can be found here, but all must be adapted to survive drying out and extreme changes in temperature.
Middle Shore – is the main tidal belt covered and uncovered at every tide cycle, dominated by brown seaweeds called wracks, barnacles, limpets, mussels, crabs, anemones and some types of green and red algae. Inhabitants must be equally able to survive exposed to air or underwater.
Lower Shore –is the lower limit of the tide only exposed for a short period of time during spring tides and is dominated by a variety of organisms including kelps and red seaweeds, There is generally a greater diversity of animals and seaweeds here due to more stable conditions.Oarweed (Laminaria digitata) on rocky shore at Mount Batten (Plymouth) at low tide
Subtidal zone – Although this is not technically within the intertidal zone, the shallow subtidal zone is occasionally exposed during extreme low water spring tides during periods of high pressure. It is home to more typically marine species, including kelps, anemones, fish and many other organisms.
Rocky shores are biologically rich environments. Species here have become adapted to deal with the extreme conditions created by the movement of the tides and many cannot be found anywhere else.
While the tide is out, barnacles, limpets, and beadlet anemones can survive being exposed in open rock because they can trap water inside their shells. Shannies and shore crabs hide in crevices and under wet rocks and seaweeds; snakelocks anemones and many seaweeds prefer to live in the rockpools. Pools are a good refuge for animals that can’t survive drying out. Nevertheless they are an extreme habitat for species to survive in, as temperature and salinity increases and oxygen can also be very low.
In the British Isles and in many parts of the world, rocky shore seaweeds, and animals such as winkles, edible crabs and kelps are commercially harvested by humans. However, care must be taken when removing seaweed and snails from the wild as the absence of a particular species may damage the balance of life on the shore. Other threats to the healthy balance of rocky shore habitats include pollution and marine litter, introduction of alien species and damage by recreational activities. Visit our species pages to find out more about some rocky shores species like crabs, starfish, seaweed, anemones and others.
- Although limpets do not move very much when the tide is out, on wet days or when underwater they become more active fighting each other for the best grazing spots.
- The tidal range in the Bristol Channel in Britain is one of the largest in the world at around 13 metres!
- Grazing animals like limpets and snails can actually help create rockpools by grinding away rock with their tough teeth.
Some key species commonly found around the British IslesFlat periwinkle (Littorina obtusata) on toothed wrack (Fucus serratus)
Limpets (Patella vulgata) – found on rocky shores with all levels of exposure in the British Isles
Shore Crabs (Carcinus maenas) – found on all types of shore in the British Isles
Cushion Starfish (Asterina gibbosa) – found on the lower shore or in rockpools
Beadlet Sea Anemones (Actinia equina) – found on all shores in the British Isles attached to rocks or in rockpools
Bladder Wrack (Fucus vesiculosus) – large type of brown seaweed found on rocky shores with all levels of exposure in the British Isles