Engineering novel habitats on urban infrastructure to increase intertidal biodiversity.

Urbanization replaces natural shorelines with built infrastructure, seriously impacting species living on these "new" shores. Understanding the ecology of developed shorelines and reducing the consequences of urban development to fauna and flora cannot advance by simply documenting changes to diversity. It needs a robust experimental programme to develop ways in which biodiversity can be sustained in urbanized environments. There have, however, been few such experiments despite wholesale changes to shorelines in urbanized areas. Seawalls--the most extensive artificial infrastructure--are generally featureless, vertical habitats that support reduced levels of local biodiversity. Here, a mimic of an important habitat on natural rocky shores (rock-pools) was experimentally added to a seawall and its impact on diversity assessed. The mimics created shaded vertical substratum and pools that retained water during low tide. These novel habitats increased diversity of foliose algae and sessile and mobile animals, especially higher on the shore. Many species that are generally confined to lowshore levels, expanded their distribution over a greater tidal range. In fact, there were more species in the constructed pools than in natural pools of similar size on nearby shores. There was less effect on the abundances of mobile animals, which may be due to the limited time available for recruitment, or because these structures did not provide appropriate habitat. With increasing anthropogenic intrusion into natural areas and concomitant loss of species, it is essential to learn how to build urban infrastructure that can maintain or enhance biodiversity while meeting societal and engineering criteria. Success requires melding engineering skills and ecological understanding. This paper demonstrates one cost-effective way of addressing this important issue for urban infrastructure affecting nearshore habitats.