The sensitivity of

Intertidal species

Reefs are widespread in Southern Europe and occur widely around the UK coast. They are very variable in form and in the communities that they support. Reefs are rocky marine habitats or biological concretions that rise from the sea bed. They are generally subtidal but may extend as an unbroken transition to the intertidal zone, where they are exposed to the air at low tide. Two main types of reef can be recognised: those where the structure is created by the animals themselves (biogenic reefs) and those where animal and plant communities grow on raised or protruding rock.

Reef communities, or ‘hold-fast’ communities, need to harness wave energy to survive. The plant and animal communities rely on turbulent conditions for nutrients, oxygen and carbon supplies. They are therefore well adapted to survive the extreme physical stresses imposed by waves and currents.

For safety reasons, water-based recreation, other than snorkelling, diving and the use of very shallow hulled craft, is unlikely to take place in the vicinity of reefs. However, land based recreation at low tide can have implications for intertidal reef habitats and communities through:

• collection of species (rock pooling)
• trampling
• littering

Intertidal Species

Rocky shores are dominated by Fucales or rock-weeds, represented by species in temperate climates such as, Ascophyllum, Cystoseira and Fucus. However, all of these plant species experience environmental stresses due to their location, which exposes them to immersion, desiccation and changes in water temperature and salinity.

It has been suggested that seaweeds and rock-weeds may suffer from nutrient deficiency but Mann (1972) concluded that some communities were able to overcome such natural limitations by storing nutrients during periods of high availability and using them for growth in the Spring and Autumn. These changes to the typical seasonal growth timing may have implications for recreational management as it suggests that the sensitivity of the plant may be greatest in its spring and autumn growth periods.

Intertidal and littoral ecosystems are exposed to human impact more frequently than any other marine system. However, it is difficult to determine generic sensitivities because of the complex relief of rocky shores. Some locational classifications do exist, which relate to where species are found on the shore (upper, mid and lower) and the levels of shading available. Alternatively species location may be determined by available space, rather than any other environmental control. These issues are considered in more detail by Hill et al (1998)

This problem with identification of sensitive areas is heightened by the fact that the community structure of some rocky shores is highly variable in time and space. Due to this variability, and the natural stress applied to the system as outlined above, impacts on one species can have serious community-wide consequences. With such a variety of natural fluctuations, human impacts may be difficult to determine without detailed and often long term investigations at site level.

The tables below summarise the potential threats to reefs from land and waterborne processes.

Water based processes

Land based processes

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