LCS structures share several physical and biological features with natural rocky shores. The structures offer new hard substrate available for colonisation by algae and benthic organisms typical of natural rocky shores. As natural rocky shores, LCS are affected by same physical and biological processes, but differ in three major aspects: they have a limited horizontal and vertical extent, they are characterised by a lower habitat complexity and finally they experience a higher disturbance.
As a result, habitat and species diversity on LCS is often lower than on rocky shores. Several environmental factors affecting epibiota are pre-determined and cannot be modified. These include:
- Geographical variability, being determined by the species pool, wave and current regimes, tidal range and salinity;
- Wave exposure and biological interactions;
- Vertical gradients according to tidal height / depth;
- Temporal variability, including colonisation processes, seasonal and long-term fluctuations;
- Disturbance by sand scouring and siltation. These factors, although outside the control of engineers, need to be taken into consideration for the construction of LCS as they will have influence on the development of epibiota.
LCS design features can be modified to minimise ecological impacts and to implement mitigation measures. Here are some simple rules that can be applied to obtain target effect or secondary management goals. Disturbance by sediment scouring and siltation can be reduced by the adding berms to the LCSs. Maintenance works can be minimised by increasing the stability of LCS and of the sea bed. More complex surfaces (e.g. textured or pitted block surfaces) and artificial rock pools can be integrated in the design of LCS to increase habitat and species diversity. Carbonate based building materials such as limestone become easily weathered and bioeroded, thus provide a variety of micro-habitats for to colonise. On macrotidal shores, LCSs that are located lower on the shorewill be colonised by a higher number of species.
Complex habitats also promote living resources such as mussels, oysters and crustaceans. These effects can enhance the recreational and amenity use of these structures by public, such as food harvesting, sport fishing and appreciation of marine life.
In conclusion, the environmental setting has an important influence on the colonisation and future development of epibiota, thus it needs to be taken into account by coastal engineers prior construction of LCS. In contrast, LCS design features are under the control of engineers and can be modified to minimise impacts and promote positive effects on recreational use and natural resources. Under the ecological viewpoint, low crested structures and other types of coastal defences lead, as most human interventions, to major modifications in the coastal ecosystem and their construction should be limited to the minimum. However, where these structures are a necessary measure against coastal erosion, attempts should be made to promote their integration in the coastal system, minimising ecological impacts and enhancing the socio-economical value.
The findings summarised above are the result of extensive studies and experiments which were carried out in the Mediterranean (Spain, Italy), Atlantic (UK) and North Sea (Denmark). This guarantees the generality of the results and provides information that can be disseminated in form of European guidelines and recommendations for an environmentally sensitive design of coastal and sea defence structures.
Several end users could benefit from the application of this result:
- The private sector, such as engineering companies involved in the design and construction of LCS and surveyors involved in the Environmental Impact Assessment and monitoring;
- The public sector, such as Environment Agencies and local councils involved in the decision making process and coastal management;
- The scientific community, especially those in the research field of anthropogenic impacts on coasts and pollution.
Taking into account the variety of target potential users, dissemination of this result will be through conference and seminars for scientific and wider audience, briefing of conservation agencies, distribution of technical reports to local councils and coastal managers, and peer reviewed international publications.
Coastal defences are increasing exponentially along most European coasts, as a consequence of erosion and flooding. However, the ecological implications of LCS and other coastal structures have been considerably neglected, despite the acknowledgement of the need for a more sustainable coastal development, which must take into account the status, protection and preservation of the ecosystem. This result can help addressing stakeholders towards an integrated and more environmentally sound coastal management, as also required by the European Habitat and Water Framework Directive.