Ecological enhancement of coastal engineering structures: Passive enhancement techniques

Mairi Macarthur,Larissa A Naylor,Jim D Hansom,Michael T Burrows

doi:10.1016/j.scitotenv.2020.139981

Mairi Macarthur, Larissa A Naylor + Show 2 more

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https://doi.org/10.1016/j.scitotenv.2020.139981

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Abstract

The rock type used in coastal engineering structures impacts biodiversity, but its effect has been understudied to date. We report here on whether different combinations of rock material and rock mass properties can improve habitat suitability and early phase ecological outcomes on coastal engineering structures. We examine two coastal engineering schemes that used different granites during construction. At site one, Shap granite boulders with a high number of cm-dm2 surface features (e.g. ledges) were deliberately positioned during construction (called passive enhancement), to a) maximise the provision of cm-dm scale intertidal habitat and b) determine which scale of habitat is best for ecological enhancement. At site two, Norwegian granite boulders were installed without passive enhancement, allowing for a direct comparison. Passive positioning of Shap granite boulders led to an increase in limpet (Patella vulgata, Linnaeus, 1758) abundance within two years but few limpets were recorded on the non-enhanced Norwegian granite. Positioning of boulder thus exerts a strong control on the mm and mm-dm scale geomorphic features present, with clear ecological benefits when suitable features are selected for and optimally positioned (i.e. passive enhancement) to maximise habitat features. An EcoRock scoring matrix was developed to aid in the selection of the most ecologically suitable rock materials for coastal engineering worldwide; this can help improve habitat provision on engineered structures in a rapidly warming world.

Highlights

We examined to extent to which rock-materials were considered as part of ecological outcomes as part of recent ecological enhancement and rocky shore ecology research (2010–2019 in Google Scholar and Web of Science, in April 2019)
We examine here the influence of boulder roughness, geomorphic features and positioning on early stage colonisation of rock armour by testing the hypotheses that: 1) Inherent rock surface complexity at a range of spatial scales positively influences early stage colonisation on coastal engineering rock armour; 2) Careful positioning of natural and artificial features on coastal engineering rock armour enhances the development of ecological communities within 2 years
Field surveys conducted in the mid-upper intertidal zone at Hartlepool in September 2016 recorded 18 species across the shore platform, with an average of 10 species per quadrat (MacArthur, 2019)

Summary

Introduction

The lack of surface topographic complexity is the main reason for emerging global evidence that such structures are poor ecological surrogates for the natural rocky shores they purport to replace, since they typically support fewer species with lower abundances (Bulleri et al, 2005; Moschella et al, 2005; Firth et al, 2014b). This alters community interactions, ecological function and ecological connectivity (Bishop et al, 2017; Strain et al, 2017).

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