BIOGEOMORPHOLOGY of COASTAL STRUCTURES: Understanding Interactions Between Hard Substrata and Colonising Organisms As a Tool for Ecological Enhancement
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BIOGEOMORPHOLOGY OF COASTAL STRUCTURES: Understanding interactions between hard substrata and colonising organisms as a tool for ecological enhancement Submitted by Martin Andrew Coombes B.Sc. M.Sc. , to the University of Exeter as a thesis for the degree of Doctor of Philosophy in Geography In February 2011 This thesis is available for Library use on the understanding that it is copyright material and that no quotation from the thesis may be published without proper acknowledgement. I certify that all material in this thesis which is not my own work has been identified and that no material has previously been submitted and approved for the award of a degree by this or any other University. Signature: M. A. Coombes --- BLANK --- 2 ABSTRACT Urbanisation is increasingly recognised as a major ecological pressure at the coast. By 2035, the Department for Environment, Food and Rural Affairs will have to spend £1 billion each year on flood defence and erosion control infrastructure if current levels of protection are to be sustained in England and Wales; this represents a substantial commitment to building new hard structures. Ecological research has shown that structures like seawalls, breakwaters, and harbour and port infrastructure are poor surrogates for undisturbed rocky shores. This, alongside substantial international policy drivers, has led to an interest in the ways in which structures might be enhanced for ecological gain. Virtually all of this research has been undertaken by ecologists, while the contribution of geomorphological understanding has not been fully recognised. This thesis presents an assessment of the two-way interactions between colonising organisms and the materials used to build hard coastal structures under a framework of biogeomorphology. The influence of material type and small-scale surface texture on early colonisation is assessed alongside detailed observations of the ways in which biota are involved in the alteration of substratum properties and behaviours through weathering and erosion in the intertidal zone. The research demonstrates that biotic (organisms) and abiotic (material substrata) components of coastal structures are inherently linked at various spatial and temporal scales through complex biogeomorphic interactions and feedbacks. Importantly, these interactions have consequences for the subsequent operation of ecological and geomorphological processes that are of relevance to urban marine ecology, weathering and rock coast geomorphology, and engineering. This thesis demonstrates the considerable potential to manipulate substratum-biota interactions on artificial structures for ecological gain, both directly and indirectly. More broadly, the explicitly interdisciplinary methodological approach adopted shows the value and necessity of integrated research for achieving useful, applied outcomes. 3 --- BLANK --- 4 ACKNOWLEDGEMENTS I would like to thank my supervisors, Larissa Naylor, Richard Thompson and also Stephen Roast for their continued support and guidance throughout my PhD. Their encouragement, unyielding enthusiasm and willingness to engage in simulating discussions have been invaluable. I have learnt an incredible amount from my supervisors during this process, both academically and personally, and for this I am extremely grateful. I thank Great Western Research and the Environment Agency for funding the research and the ENCORA Project, the British Society for Geomorphology and the University of Exeter College of Life and Environmental Sciences for additional financial support. Robert Fairhurst, Gavyn Rollinson and Sharon Uren are thanked for microscope training, and I am particularly grateful to Lluis Gómez-Pujol, Joan Fornós and technical staff at the University of the Balearic Islands for invaluable guidance and discussions on Scanning Electron Microscopy work, as well as their kind hospitality. I thank Stephan Harrison, Jasper Knight and John Coggan for helpful suggestions during the early stages of the research and Brian Helmuth, Paula Moschella and Cherith Moses for kindly supplying valuable reference material. Alan Trenhaile, Bernie Smith and Alejandra Feal-Pérez are thanked for helpful suggestions on laboratory procedures and Drummond Masterton for his assistance with laser scanning procedures and analysis. Joe Burdon kindly assisted with fieldwork and in obtaining mapping data at Tregear Point. Orlando Venn and Tim O’shea are also thanked for valuable discussions during the application of some of the ideas developed in the thesis as part of the Shaldon and Ringmore Tidal Flood Defence Scheme. I must thank a great many people and organisations that have assisted with the practical aspects of this research: the National Trust, The Duchy of Cornwall, English Nature, Cornwall Council, Nicky Monies, and Stuart and Samantha Smith are thanked for allowing access to work at Gala Rocks and Tregear Point; Rob Lawson, Andrew Munson, and Nick Browning and James Radcliffe for their co- 5 operation and permissions for access and sampling at Ilfracombe Harbour, Newlyn Harbour and West Bay Harbour; Ian Skinner and Ennstone Johnston Ltd. (now Breedon Aggregates Ltd.), Andrew Jackson and Stone Firms Ltd., and Debbie Palmer and Aaram Resources Ltd. for supplying rock materials; staff at the University of Plymouth Marine and Diving centre, the Ministry of Defence and Juliette Jackson for permissions and assistance with fieldwork on Plymouth Breakwater; Leslie Randle for concrete sample preparation, Ian Faulks for guidance on geomechanical laboratory procedures and Steve Pendray for putting up with my endless pestering to cut more rock samples. Personally, I owe so much to my partner, Adam, for his unwavering support from the very beginning – through thick and thin. I can honestly say I could not have done this without you – thank you so much. Finally, I am eternally grateful to my family, particularly my parents, who have remained ever supportive throughout my education. Mum this is for you. 6 TABLE OF CONTENTS CHAPTER 1. INTRODUCTION AND THESIS AIMS .............................................................................33 1.1 Coastal Structures and Biodiversity ....................................................................................33 1.2 A Biogeomorphological Approach ......................................................................................35 1.3 Research Aims and Thesis Structure...................................................................................37 CHAPTER 2. BACKGROUND............................................................................................................43 2.1 Introduction ......................................................................................................................43 2.2 Environmental, Economic and Social Assets and the Need for Coastal Defence ..................45 2.2.1 Coastal Flood and Erosion Risk Management in the UK ..............................................48 2.2.2 Current and future commitments to hard defence in the UK ......................................49 2.3 Urban Marine Ecology: Structures as habitats ....................................................................55 2.3.1 Direct impacts of hard structures on coastal ecology ..................................................58 2.3.2 Indirect impacts of hard structures on coastal ecology ...............................................60 2.3.3 Factors affecting ecological processes on artificial structures .....................................61 2.3.4 Artificial structures as habitats: conclusions ...............................................................69 2.4 Policy Drivers for Ecological Enhancement .........................................................................70 2.4.1 The Water Framework Directive (WFD) ......................................................................70 2.4.2 Other environmental legislation .................................................................................73 2.4.3 Planning regulations ..................................................................................................74 2.5 Maximising Ecological Potential: Progress, limitations and opportunities ...........................76 2.5.1 Existing guidance and applied testing .........................................................................76 2.5.2 Ecological enhancement and engineering durability ...................................................83 7 2.6 Geomorphology and Coastal Structures ............................................................................. 85 2.6.1 The current role of geomorphology in the design of coastal structures ...................... 85 2.6.2 Rock coast geomorphology and weathering science in urban marine ecology ............ 86 2.6.3 Potential contributions to theory ............................................................................... 93 2.7 Limitations of Marine Urban Ecology: The geomorphological contribution ........................ 93 2.7.1 Representative materials ........................................................................................... 94 2.7.2 Manipulation of small-scale habitat heterogeneity .................................................... 96 2.7.3 Substratum geomorphological properties and behaviours ......................................... 96 2.8 Summary and Conclusions ................................................................................................. 97 CHAPTER 3. CONCEPTUAL OVERVIEW & RESEARCH FRAMEWORK