The sensitivity of a community is its ability to withstand and recover from disturbance. Some rocky shore communities are naturally unstable. This may be due to frequent physical disturbance. For example, chalk shores of the South Wight Maritime are unstable due to natural erosion. The rapid rate of erosion frequently exposes bedrock and prevents the development of stable, ‘mature’ communities. On such shores, additional low level impacts may make little difference to natural variability in species numbers and abundance. In many cases, natural instability results from a combination of stochastic events and intense biological interaction. These communities are particularly at risk from anthropogenic disturbance which could easily swing the balance in favour of one species or further destabilise the community.

The aftermath of oil spills demonstrates the vulnerability of rocky shore communities to acute impacts. Chemical dispersants and mechanical cleaning can do even more damage to the community than the oil itself. In many cases, the best course of action when spilt oil reaches a shore will be to leave it to disperse naturally. While rocky shores can recover from extensive acute impacts, this process takes a considerable time on a scale of tens of years when large stretches of coast are affected.

Localised disturbance to rocky shore communities will be caused by dumping or building on the shore. The local hydrodynamic regime and the degree of wave action experienced by the shore may be affected by developments, including moorings, further out to sea. A rigorous monitoring programme should be employed to detect the potential impacts of any new development.

Acute impacts are more easily detected and better studied than the more subtle effects of chronic factors. However, research did allow the adverse effects of TBT to be characterised and led to legislative changes. This illustrates the importance of research. The use of Ivermectin on fish farms is currently a cause for concern. Any expansion in the use of this chemical should be accompanied by targeted research to assess its impact on marine invertebrates and its ultimate effect on communities. The recreational use of shores has been shown to have negative effects on the shore community. Research is strongly encouraged, especially within SACs to investigate ways of minimising this impact without severely restricting public enjoyment of the shore. The presence of rubbish on the shore reduces its aesthetic appeal. Any objects which are heavy enough to smash encrusting organisms might result in increased physical disturbance to the shore community.

Although Sargassum muticum and Elminius modestus appear to have fitted into UK rocky shore communities without causing severe disruption, introduced species present a real threat. Undaria may prove to be a more damaging invader if it gets a foothold in the UK. Introduced species will have a severe impact when they displace other species. This could result in the local extinction of the displaced species. Global extinctions are unlikely as the various physical factors which affect rocky shores would be expected to check and limit the spread of the invader. Serious community level repercussions could occur if the displaced species provides microhabitats for other species or if it plays a key role in structuring the community.

Next Section                         References