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Seagrass As an Indicator of Estuary Condition for the Swan-Canning Estuary

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Seagrass As an Indicator of Estuary Condition for the Swan-Canning Estuary Government of Western Australia Department of Water Seagrass as an indicator of estuary condition for the Swan-Canning estuary Report no. WST 62 January 2014 Water Science Technical Series, report no. 62 Seagrass as an indicator of estuary condition for the Swan-Canning estuary Department of Water Water Science Technical Series Report no. 62 January 2014 Department of Water 1 Department of Water 168 St Georges Terrace Perth Western Australia 6000 Telephone +61 8 6364 7600 Facsimile +61 8 6364 7601 National Relay Service 13 36 77 www.water.wa.gov.au © Government of Western Australia January 2014 This work is copyright. You may download, display, print and reproduce this material in unaltered form only (retaining this notice) for your personal, non-commercial use or use within your organisation. Apart from any use as permitted under the Copyright Act 1968, all other rights are reserved. Requests and inquiries concerning reproduction and rights should be addressed to the Department of Water. ISSN 1836-2869 (print) ISSN 1836-2877 (online) ISBN 978-1-922124-68-5 (print) ISBN 978-1-922124-69-2 (online) Acknowledgements This project was funded by the Government of Western Australia through the Swan River Trust and the Department of Water. The Department of Water would like to thank the following for their contribution to this publication: • Kieryn Kilminster and Vanessa Forbes for study design and report writing • Artemis Kitsios, Peter Kretschmer, Helen Nice, Ben Marillier, Anne Brearley, Bronwyn Rennie, Zöe Goss, Sarah Evans, Georgina Evans, Frances Miller, Tim Storer, Karl Hennig, Dominic Heald, Belinda Quinton, Kelli O’Neill, Jeff Cosgrove and Kerry Trayler for field and lab work • Lisa Dinnis and Mark Shackleton for assistance with data analysis • Marianne Holmer, Jim Fourqurean, Kathryn McMahon, Paul Lavery, Catherine Collier, Mads Thomsen and Thomas Wernberg for their advice on study design at the project’s outset • Kingsley Dixon at the Botanic Gardens and Parks Authority for providing access to the Kings Park Laboratories and to Eric Bunn, Annette Johnson, Wolf Lewandrowski and Jason Stevens for their help while at Kings Park • Marianne Holmer, Di Walker, Gary Kendrick, Marion Cambridge and Anne Brearley for their insightful discussions about our findings. • Many thanks also to Malcolm Robb for his support of this project. • Symbols for diagrams courtesy of the Integration and Application Network (ian.umces.edu/symbols). 2 Department of Water Reference details The recommended citation for this publication is: Kilminster & Forbes 2014, Seagrass as an indicator of estuary condition in the Swan-Canning estuary, Water Science Technical Series, report no. 62, Department of Water, Western Australia. For more information about this report, contact Kieryn Kilminster, Water Science Branch, Department of Water. Cover photograph: Shallow seagrass meadow of Halophila ovalis overlain by macroalgae at Lucky Bay looking towards Perth city in the Swan-Canning estuary (photo credit: KL Kilminster). Disclaimer This document has been published by the Department of Water. Any representation, statement, opinion or advice expressed or implied in this publication is made in good faith and on the basis that the Department of Water and its employees are not liable for any damage or loss whatsoever which may occur as a result of action taken or not taken, as the case may be in respect of any representation, statement, opinion or advice referred to herein. Professional advice should be obtained before applying the information contained in this document to particular circumstances. This publication is available at the Swan River Trust website (www.swanrivertrust.wa.gov.au) or for those with special needs it can be made available in alternative formats such as audio, large print or Braille by contacting the Department of Water. Water Science Technical Series, report no. 62 Contents Contents ...................................................................................................................... v Summary .................................................................................................................... xi 1 Introduction .............................................................................................................. 1 1.1 Seagrass fundamentals ...................................................................................................... 1 1.2 Ecosystem value of seagrasses ......................................................................................... 2 1.3 Threats to seagrass ............................................................................................................ 3 Nutrients ........................................................................................................................................ 3 Light reduction .................................................................................................................................. 4 Algae and seagrasses ....................................................................................................................... 5 Sediments ........................................................................................................................................ 6 Physical disturbances ........................................................................................................................ 7 Invasive species ................................................................................................................................ 7 Pollutants ........................................................................................................................................ 7 1.4 Management implications ................................................................................................... 8 Ecological indicators.......................................................................................................................... 8 1.5 Seagrasses as biological indicators ................................................................................... 9 Halophila ovalis as an ecological indicator........................................................................................ 10 2 Project overview and site descriptions................................................................... 11 2.1 Overview of sampling program .........................................................................................11 2.2 Overview of sites ..............................................................................................................13 Site RCK ...................................................................................................................................... 14 Site DLK ...................................................................................................................................... 15 Site LUB ...................................................................................................................................... 16 Site HTH ...................................................................................................................................... 17 Site CAN ...................................................................................................................................... 18 Site PPT ...................................................................................................................................... 19 Water depth .................................................................................................................................... 20 3 Site and estuary conditions ................................................................................... 21 3.1 Rainfall ..............................................................................................................................21 3.2 Swan-Canning routine data ..............................................................................................22 Temperature and salinity ................................................................................................................. 22 Water column nutrients.................................................................................................................... 25 3.3 Characterisation of sediment type at each site ................................................................30 4 Changes in environmental and biological variables over time ............................... 33 4.1 Temperature .....................................................................................................................33 4.2 Photosynthetically active radiation (PAR) ........................................................................33 4.3 Water quality .....................................................................................................................38 4.4 Field observations of macroalgae and seagrass ..............................................................40 4.5 Seagrass production measures ........................................................................................43 4.6 Seagrass meadow measurements (from cores) ..............................................................46 4.7 Reproduction.....................................................................................................................48 4.8 Seagrass chemical analysis .............................................................................................51 4.9 Seagrass biometrics (WinRHIZO)
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