Artificial coastal defence structures as surrogate habitats for natural rocky shores

: Giving nature a helping hand

Abstract

Engineered coastal defence structures are proliferating around coastlines globally to protect expanding urban developments from predicted sea level rise and extreme weather events. In response to evolving marine planning policies, it is becoming increasingly necessary to incorporate ecologically-sensitive design into coastal developments, not only to minimise their environmental impacts, but also to maximise potential ecological and socio-economic secondary benefits. I investigated coastal defence structures as surrogate habitats for rocky shore biodiversity, and the potential for the design of structures to be manipulated to achieve more beneficial outcomes. I focused on three major knowledge gaps that must be addressed in order to effectively incorporate ecologically-sensitive design into coastal defences: (i) the capacity to predict ecological responses to different engineering designs for coastal defence structures; (ii) the potential for ecological engineering interventions to enhance biodiversity on structures; and (iii) stakeholder perceptions regarding the desirability of potential secondary benefits that can be built-in to developments. To address the first knowledge gap, I surveyed 125 intertidal coastal defence structures around the coast of Wales, UK, and modelled the relationship between a number of physico-environmental parameters and the biological communities colonising each structure. Using these data I developed a predictive tool and demonstrated that, given the nature of the shoreline on which a new coastal defence was required (i.e. the surrounding sediments and level of exposure to prevailing wind and waves), it would be possible to predict (with up to 62% confidence) the characteristic community that could be expected to colonise a structure, based on its broad shape, position in the intertidal zone, and abundance of microhabitats. To address the second knowledge gap, I explored the potential for a novel ecological engineering intervention (drill-cored artificial rock pools) to enhance biodiversity on an intertidal riprap breakwater. Over a 30- month period, I found that the artificial pools performed an important ecological function on the structure. They were utilised by numerous species that were not otherwise recorded on surrounding emergent rock surfaces, including taxa that have frequently been reported to be absent or scarce on coastal defences previously (e.g. mobile fauna, lower-shore taxa and proportionally-rarer taxa). Furthermore, the artificial pools were just as productive as natural rock pools and supported a comparable number of species. The composition of communities in artificial and natural pools, however, was different, largely on account of differences in sessile assemblages (i.e. algae and encrusting fauna). The intervention, nevertheless, was an effective and affordable means of ecological enhancement, and has received considerable interest from industry and practitioners. To address the third knowledge gap, I investigated stakeholder attitudes regarding desirability of different potential secondary benefits that may be built-in to coastal developments. Although this study revealed complex and nuanced perceptions across sectors, there was unanimous support for implementing multi-functional coastal defence structures in place of traditional single-purpose ones, and in general the most desirable secondary benefits were ecological ones (prioritised over social, economic and technical benefits). In this thesis I evaluate these outcomes in the context of their application to marine planning and conservation management. I finally conclude by outlining the steps that are necessary to achieve wide-scale and effective implementation of ecologically sensitive and multi-functional design for artificial coastal defence structures that are becoming ubiquitous features of urban coastlines globally

Date of Award	26 Jan 2016
Original language	English
Awarding Institution	Aberystwyth University
Sponsors	Knowledge Economy Skills Scholarships
Supervisor	Philippa Moore (Supervisor) & Michael Christie (Supervisor)