Between a rock and a hard place: Environmental and engineering considerations when designing coastal defence structures

Coastal defence structures are proliferating as a result of rising sea levels and stormier seas. With the realisation that most coastal infrastructure cannot be lost or removed, research is required into ways that coastal defence structures can be built to meet engineering requirements, whilst also providing relevant ecosystem services—so-called ecological engineering. This approach requires an understanding of the types of assemblages and their functional roles that are desirable and feasible in these novel ecosystems. We review the major impacts coastal defence structures have on surrounding environments and recent experiments informing building coastal defences in a more ecologically sustainable manner. We summarise research carried out during the THESEUS project (2009–2014) which optimised the design of coastal defence structures with the aim to conserve or restore native species diversity. Native biodiversity could be manipulated on defence structures through various interventions: we created artificial rock pools, pits and crevices on breakwaters; we deployed a precast habitat enhancement unit in a coastal defence scheme; we tested the use of a mixture of stone sizes in gabion baskets; and we gardened native habitat-forming species, such as threatened canopy-forming algae on coastal defence structures. Finally, we outline guidelines and recommendations to provide multiple ecosystem services while maintaining engineering efficacy. This work demonstrated that simple enhancement methods can be cost-effective measures to manage local biodiversity. Care is required, however, in the wholesale implementation of these recommendations without full consideration of the desired effects and overall management goals

Effects of a mucilage event on the Mediterranean gorgonian Paramuricea clavata. I - Short term impacts at the population and colony levels.

A Paramuricea clavata population thriving between 29 and 39 m depth on a shoal at the northern entrance to the Strait of messina was affected by mucilage coverage at the end of summer 1993. Mucilage become entangled in projecting branches and necrotized the coenenchyme below, leaving the axial skeleton bare. The entire population was heavily affected, extent of injuries being negatively correlated with size of colonies.Colony size, scale and location of damage were related to successful regeneration after six months