Fal and Helford SAC: Subtidal Seagrass Condition Assessment 2015 Report Number: ER15-289 Performing Company: Sponsor: Natural England Ecospan Environmental Ltd Framework Agreement No. 22643/04 Unit 8 Strashleigh View Ecospan Project No: 15-362 Lee Mill Industrial Estate Ivybridge Devon PL21 9GS Tel: 01752 897198 Email: [email protected] www.ecospan.co.uk Ecospan Environmental Ltd. is registered in England No. 5831900 ISO 9001 Fal and Helford SAC: Subtidal Seagrass Condition Assessment 2015 Author(s): L.A. Curtis Approved By: M.D Field Date of Approval: 12.11.15 Circulation 1. Annie Jenkin Natural England 2. Trudy Russell Natural England 3. Mike Field Ecospan Environmental Ltd ER15-287 Page 2 of 89 Fal and Helford SAC: Subtidal Seagrass Condition Assessment 2015 All maps within this document are subject to Crown Copyright protection unless otherwise stated © Crown copyright. All rights reserved. Natural England, 100017954 [2015]. CONTENTS EXECUTIVE SUMMARY ...................................................................................................... 9 1. INTRODUCTION ......................................................................................................... 11 1.1 Study Area ........................................................................................................ 11 1.2 Condition Monitoring of the Seagrass Bed Community Sub-feature of the Fal and Helford SAC. ....................................................................................................................... 13 2. AIMS AND OBJECTIVES ............................................................................................ 15 3. METHODS ................................................................................................................... 15 3.1 Seagrass DD/TV survey .................................................................................... 15 3.1.1 DD/TV Survey Dates ...................................................................................... 22 3.1.2 Quality Assurance .......................................................................................... 22 3.2 Dive Survey ....................................................................................................... 23 3.2.1 Locations and Settings of Sample Transects ................................................. 23 3.2.2 Post Dive Analysis ......................................................................................... 24 4. RESULTS .................................................................................................................... 26 4.1 Attributes Measured Using DD/TV ..................................................................... 26 4.1.1 Quality Assurance .......................................................................................... 26 4.2 Attributes Measured Using Diving Methods ....................................................... 26 4.2.1 Exploration of Correlations ............................................................................. 27 4.3 Percuil River (Upper and Lower) ....................................................................... 27 4.4 St. Mawes Harbour ............................................................................................ 27 4.4.1 Attributes Measured Using DD/TV ................................................................. 28 4.4.2 Attributes Measured Using Diving Methods ................................................... 29 4.5 Amsterdam Point to Carricknath Point ............................................................... 30 4.5.1 Attributes Measured Using DD/TV ................................................................. 30 4.5.2 Attributes Measured Using Diving Methods ................................................... 31 4.6 West of Carricknath Point .................................................................................. 32 4.7 St. Mawes Bank ................................................................................................ 33 4.7.1 Attributes Measured Using DD/TV ................................................................. 34 4.7.2 Attributes Measured Using Diving Methods ................................................... 35 4.8 Penarrow Point .................................................................................................. 35 4.8.1 Attributes Measures Using DD/TV Methods ................................................... 36 4.8.2 Attributes Measured Using Diving Methods ................................................... 37 4.9 Flushing ............................................................................................................ 37 ER15-287 Page 3 of 89 Fal and Helford SAC: Subtidal Seagrass Condition Assessment 2015 4.10 Gyllyngvase and Swanpool ............................................................................... 39 4.11 Maenporth ......................................................................................................... 40 4.12 Helford - Polgwidden Cove to Toll Point, East of Passage Cove and Bosahan....................................................................................................................... 41 4.12.1 Polgwidden Cove to Toll Point ....................................................................... 41 4.12.2 East of Passage Cove and Bosahan .............................................................. 44 4.13 Gillan Creek ...................................................................................................... 45 4.14 Parbean Cove ................................................................................................... 45 4.15 Porthallow Cove ................................................................................................ 46 5. DISCUSSION .............................................................................................................. 48 5.1 Comparisons Between Seagrass Beds in the Fal and Helford SAC................... 48 5.2 Temporal Comparisons and Condition Assessment .......................................... 52 5.2.1 Limitations of Data ......................................................................................... 53 5.2.1.1 Seagrass Percentage Cover and Extent ..................................................... 53 5.2.1.2 Attributes assessed by diving ..................................................................... 55 5.2.1.3 Comparisons of Seagrass Bed Extent ........................................................ 56 Percuil River ................................................................................................................ 56 St. Mawes Harbour ...................................................................................................... 57 Amsterdam Point to Carricknath Point ......................................................................... 57 St. Mawes Bank ........................................................................................................... 58 Penarrow Point ............................................................................................................ 59 Flushing ....................................................................................................................... 60 Gyllyngvase and Swanpool .......................................................................................... 61 Maenporth .................................................................................................................... 62 Polgwidden Cove to Toll Point ..................................................................................... 63 East of Passage Cove and Bosahan ............................................................................ 64 Gillan Creek ................................................................................................................. 65 Parbean Cove .............................................................................................................. 66 Porthallow Cove ........................................................................................................... 67 5.2.1.4 Comparisons of Plant Density .................................................................... 68 5.2.1.5 Comparisons of Plant Length ..................................................................... 68 5.2.1.6 Comparisons in Occurrence of Leaf Infection ............................................. 69 5.2.1.7 Comparisons of Epiphyte Cover ................................................................. 69 5.2.1.8 Anthropogenic Influences ........................................................................... 69 5.2.1.9 Summary of all Attributes and Condition Assessment ................................ 70 6. CONCLUSIONS ........................................................................................................... 77 ER15-287 Page 4 of 89 Fal and Helford SAC: Subtidal Seagrass Condition Assessment 2015 7. RECOMMENDATIONS FOR FUTURE CONDITION ASSESSMENT OF THE SUBTIDAL SEAGRASS SUB-FEATURE IN THE FAL AND HELFORD SAC...................... 78 REFERENCES ................................................................................................................... 80 APPENDIX 1: Percentage Cover Raw Data Plots .............................................................. 82 APPENDIX 2: Quality Control Analysis Results .................................................................. 88 APPENDIX 3: T-test probabilities for the differences between mean attribute data