Coastal construction

Natural shorelines are replaced with artificial substrata for a variety of reasons. The most extensive changes result from the building of coastal defences. Land reclamation schemes and many waterfront developments including harbours, marinas and even residential complexes, involve the introduction of an artificial substratum into the littoral zone. Sea defences are most likely to be built on depositing shore lines and consequently they increase the substratum available to rocky shore species. However, the ecological value of these artificial substrata depends very much on their design.

Colonisation of virgin artificial substrata and subsequent succession is similar to that observed on natural substrata (Hawkins et al., 1983; Cannon, 1997). The time for a ‘mature’ community to develop is therefore expected to depend on the scale of the development. Smooth sea walls have limited topographical complexity and therefore, provide little in the way of microhabitats. As a result, an impoverished community might be expected on these structures. However, more complex hexagonal blocks and tetrapods which are sometimes used for the construction of coastal defences may provide abundant microhabitat space which could lead to a greater diversity than is seen on natural substrata. Studies of the fauna associated with artificial reefs made from concrete and stabilised coal ash have suggested that there is no substantial biological risk associated with leachates and bioaccumulation of toxins from these materials.

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