Rock armour for birds and their prey: ecological enhancement of coastal engineering

Abstract

The authors present key design, construction and ecological enhancement criteria for sustainable coastal defence structures at Hartlepool, UK, a high-energy wave climate. Such ‘ecologically favourable’ coastal defences fulfil the habitats directive and key engineering and cost criteria. Bird, rocky intertidal ecological and biogeomorphological data underpin recommendations for ‘passive’ enhancement mitigation to maximise ecological potential involving rock armour material choice (partially enhanced) and its smart positioning (enhanced). Within 12–18 months of installation, key intertidal species (e.g. limpets, barnacles, fucoid seaweeds) had successfully colonised the rock revetment, matching the initial baseline biotope. However, species abundance and overall mobile and sessile species were not significantly different between the two enhanced treatments after 12–18 months. Importantly, key prey species (the limpet, Patella vulgata) on enhanced rock armour showed statistically significant abundances similar to the baseline shore platform and significantly higher than partially enhanced rock armour. These preliminary data show that well-chosen rock armour material and boulder enhancement using positioning can match baseline biotope conditions in 12–18 months and that for some key prey species, positioning-enhanced rock armour rapidly matches baseline conditions. This facilitates rapid rock revetment colonisation, enabling good recruitment of food species and favourable conditions for internationally designated waterbird species.