Ecological impact of coastal defence structures on sediment and mobile fauna: Evaluating and forecasting consequences of unavoidable modifications of native habitats

We analyse the effects of coastal defence structures, mainly low crested (LCS), on the surrounding intertidal and subtidal infaunal assemblages and mobile fauna. The results summarise joint studies within the DELOS project in Spain (Mediterranean Sea), Italy (Adriatic Sea) and UK (English Channel and Atlantic Ocean). We demonstrate that univariate analysis did not generally identify LCS impacts, but multivariate analyses did, this being a general trend across all locations and countries. Changes in sediment and infauna seem to be inevitable and usually tend to induce negative changes, particularly on the landward side and in the presence of additional structures or after beach nourishment. The consequences of LCS construction always depend on the response of the assemblages inhabiting a given region. However, to assess the ecological importance of the induced changes and to provide additional monitoring criteria, likely indicator species should be taken into account. The presence of species either coming from the new hard bottoms or associated to physical disturbances is viewed as a negative impact, while the potential nursery role of LCS is a positive one. The combined use of monitoring and forecast models allows to identify these impacts and may play a relevant role in mitigation protocols. Finally, our work supports the feasibility of introducing design criteria tending to facilitate a positive evolution of the assemblages surrounding the structures once the changes due to the presence of the LCS are completed and the new situation tends to become more stable.