Ecosystem services provided by Modiolus modiolus biogenic reefs Flora Kent B.Sc. A thesis submitted for the degree of Doctor of Philosophy School of Life Sciences Heriot-Watt University Edinburgh UK July 2015 The copyright in this thesis is owned by the author. Any quotation from the thesis or use of any of the information contained in it must acknowledge this thesis as the source of the quotation or information. Abstract Ecological field studies were carried out in situ on Modiolus modiolus biogenic reefs throughout the UK to quantify the functional importance of these habitats and the associated ecosystem services that they provide to society. Using a combination of techniques, including Underwater Visual Censuses (UVCs), video transects and pot fishing, the key species associated with M. modious reefs were found to be Buccinum undatum and Aequipecten opercularis. B. undatum catches were three times higher on the M. modiolus reefs compared to adjacent habitats and the UVCs showed that A. opercularis were five times more abundant on M. modiolus reef sites. By providing a habitat for these commercially important shellfish, M. modiolus reefs act as an Essential Fish Habitat and support sustainable livelihoods. M. modiolus are ecosystem engineers and can occur as dense aggregations, which form raised, three dimensional reef structures on the seabed. A new method was developed to measure M. modiolus biodeposition rates in situ and this provides the first evidence of the scale at which M. modiolus are able to enhance sedimentation and contribute to the downward flux of material to the seabed. M. modiolus biogenic reefs are recognised as biodiversity hotspots and protected in Marine Protected Areas. However, under controlled conditions when subject to seawater temperatures above those experienced in the wild, byssus thread production is compromised whilst biodeposition rates are modified also. M. modiolus reefs at the southern limit of their known distribution will continue to exist in the short term but with predicted increased seawater temperature, M. modiolus may not be able to function to their full ability. These habitats are vulnerable to physical impact from mobile fishing gear and the results presented here suggest that reef recovery through byssus attachment and clump formation would be limited, especially in southern populations. Management of protected reefs should take this into account and ensure that ecosystem resilience is maximised through well enforced management measures. Acknowledgements I would like to thank my supervisors, Bill Sanderson and Kim Last for their advice and encouragement. I am sincerely grateful for the support of the Heriot-Watt Scientific Dive Team especially, Dan Harries, Hamish Mair, Rob Cook, Jo Porter, Sally Rouse and Bill Sanderson, as without their help and positivity the fieldwork would not have been possible or as enjoyable. Many thanks also to skippers Colin Moore, Bob Anderson and Peter Jones for their skill and advice. I am also grateful to Jason Newton at SUERC for his assistance with the stable isotope project as well as Christine Beveridge and Kieran Tulbure for their assistance in the aquarium at SAMS. Thanks to Mark Gray for facilitating a successful partnership with the Pen Llŷn fishermen and providing access to fishing vessels. That leads me on to thank the main funders of this PhD, which were MASTS and Heriot-Watt University as well as Seafish who supported the whelk fishing project. Many thanks also to Charlie Lindenbaumn and Karen Robinson at Natural Resources Wales for their help with habitat mapping. Finally, I would like to thank my friends and family for encouraging me to take on this challenge and supporting me throughout the PhD. ACADEMIC REGISTRY Research Thesis Submission Name: Flora Kent School/PGI: School of Life Sciences Version: (i.e. Final Degree Sought PhD First, Resubmission, (Award and Final) Marine Ecology Subject area) Declaration In accordance with the appropriate regulations I hereby submit my thesis and I declare that: 1) the thesis embodies the results of my own work and has been composed by myself 2) where appropriate, I have made acknowledgement of the work of others and have made reference to work carried out in collaboration with other persons 3) the thesis is the correct version of the thesis for submission and is the same version as any electronic versions submitted*. 4) my thesis for the award referred to, deposited in the Heriot-Watt University Library, should be made available for loan or photocopying and be available via the Institutional Repository, subject to such conditions as the Librarian may require 5) I understand that as a student of the University I am required to abide by the Regulations of the University and to conform to its discipline. * Please note that it is the responsibility of the candidate to ensure that the correct version of the thesis is submitted. Signature of Date: 23/10/2015 Candidate: Submission Submitted By (name in capitals): Signature of Individual Submitting: Date Submitted: For Completion in the Student Service Centre (SSC) Received in the SSC by (name in capitals): Method of Submission (Handed in to SSC; posted through internal/external mail): E-thesis Submitted (mandatory for final theses) Signature: Date: Table of Contents Chapter 1. General Introduction .................................................................................... 1 Ecosystem Goods and Services ................................................................................. 2 Essential Fish Habitat ................................................................................................ 5 Nutrient Cycling ........................................................................................................ 7 Sediment Stabilisation and Accumulation ................................................................ 7 Biodeposition and Filter Feeding .............................................................................. 8 Reef Formation........................................................................................................ 10 Anthropogenic Impacts on Marine Ecosystems ...................................................... 11 Objectives and Thesis Structure .................................................................................. 13 Chapter 2. Key megafaunal species associated with Modiolus modiolus reefs .............. 15 Abstract ..................................................................................................................... 15 Introduction ................................................................................................................. 15 Methods ....................................................................................................................... 19 Modiolus modiolus Reef Food Web Analysis - Stable Isotopes ............................. 22 Data Analysis .......................................................................................................... 23 Results ....................................................................................................................... 26 Habitat Surveys ....................................................................................................... 26 Underwater Visual Censuses – Megafauna Transects ............................................ 27 Drop Down Video Transects – Megafauna Transects ............................................ 28 Foodweb Analysis ................................................................................................... 31 Biological Traits Analysis ....................................................................................... 32 Discussion ................................................................................................................... 33 Chapter 3. The functional role of a horse mussel (Modiolus modiolus) reef as a habitat for the common whelk, Buccinum undatum. .................................................................. 37 Abstract ....................................................................................................................... 37 Introduction ................................................................................................................. 37 Methods ....................................................................................................................... 39 Age Determination - Growth Rate .......................................................................... 42 Migration ................................................................................................................. 43 Data Analysis .......................................................................................................... 43 Results ......................................................................................................................... 44 Growth Rates ........................................................................................................... 48 Tagged whelks ........................................................................................................ 50 Discussion ................................................................................................................... 50 Chapter 4. In situ measurements of sedimentation and biodeposition on a Modiolus modiolus reef ................................................................................................................... 54 Abstract ......................................................................................................................