Technical information supporting the 2018 seagrass (cover within sampling sites) trend and condition report card DEW Technical note 2018/34 Technical information supporting the 2018 seagrass (cover within sampling sites) trend and condition report card Department for Environment and Water June 2018 DEW Technical note 2018/34 Department for Environment and Water GPO Box 1047, Adelaide SA 5001 Telephone National (08) 8463 6946 International +61 8 8463 6946 Fax National (08) 8463 6999 International +61 8 8463 6999 Website www.environment.sa.gov.au Disclaimer The Department for Environment and Water and its employees do not warrant or make any representation regarding the use, or results of the use, of the information contained herein as regards to its correctness, accuracy, reliability, currency or otherwise. Department for Environment and Water and its employees expressly disclaims all liability or responsibility to any person using the information or advice. Information contained in this document is correct at the time of writing. This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/. © Crown in right of the State of South Australia, through the Department for Environment and Water 2018 ISBN 978-1-925668-77-3 Preferred way to cite this publication DEW (2018). Technical information supporting the 2018 seagrass (cover within sampling sites) trend and condition report card. DEW Technical note 2018/34, Government of South Australia, Department for Environment and Water, Adelaide. Download this document at https://data.environment.sa.gov.au DEW Technical note 2018/34 ii Acknowledgements This document was prepared by Nigel Willoughby and Craig Meakin (both DEW). Simon Bryars (DEW) provided principal oversight throughout. Dr Tom Prowse (The University of Adelaide) provided an early sounding board regarding the general analysis methods used, their interpretation into classes and basic diagnostic checks on the results of Bayesian analyses. Improvements were made to this report and associated report card based on reviews by Simon Bryars, Colin Cichon, Ben Smith, Fi Taylor, Michelle Bald and Sandy Carruthers (all DEW) and Matt Nelson and Sam Gaylard (both Environment Protection Authority). DEW Technical note 2018/34 iii Contents Acknowledgements iii Contents iv Summary 6 1 Introduction 1 1.1 Seagrass 1 1.2 Environment trend and condition reporting 1 1.2.1 Environmental trend and condition report card continual improvement 2 2 Methods 3 2.1 Indicator 3 2.2 Data sources 3 2.3 Analysis 3 2.4 Reliability 5 2.5 Software 6 3 Results 8 3.1 State-level 8 3.1.1 Trend 8 3.1.2 Current value 9 3.1.3 Overall change 10 3.1.4 Model result 11 3.2 Region-level 12 3.2.1 Trend 12 3.2.2 Current value 14 3.2.3 Change 15 3.2.4 Model result 16 3.3 Reliability 17 4 Discussion 18 4.1 Trend and condition 18 4.2 Extent 18 5 Appendix 19 6 References 26 DEW Technical note 2018/34 iv List of figures Figure 1 South Australian NRM regions 5 Figure 2 Distribution of credible values of statewide slope (over all years) 9 Figure 3 Estimated proportion of sites in each condition class statewide 10 Figure 4 Distribution of credible values of statewide change in cover within sampling sites of seagrass between 2009 and 2016 11 Figure 5 Plot of model results along with raw data 12 Figure 6 Distribution of credible values for NRM Region slope (over all years) 13 Figure 7 Trend in regional cover within sampling sites of seagrass 14 Figure 8 Estimated proportion of sites in each condition class in each NRM Region 15 Figure 9 Distribution of credible values of regional change in cover within sampling sites of seagrass between 2009 and 2016 16 Figure 10 Plot of regional model results, including original data points 17 List of tables Table 1 Definition of trend classes used 4 Table 2 Definition of condition classes used 4 Table 3 Guides for applying information currency 5 Table 4 Guides for applying information applicability 6 Table 5 Guides for applying spatial representation of information (sampling design) 6 Table 6 R (R Core Team 2017) packages used in the production of this report 6 Table 7 Sites at which seagrass cover was measured in each NRM Region and Year. 8 Table 8 Likelihood of each trend class 8 Table 9 Estimated proportion of sites statewide in each condition class for the last year with data (2016). 9 Table 10 Estimated statewide change in cover within sampling sites of seagrass between 1990 and 2015 10 Table 11 Likelihood of each trend class 12 Table 12 Likelihood of each condition class, estimate and credible intervals for cover within sampling sites of seagrass for the last year with data at the region level 14 Table 13 Estimated regional change in cover within sampling sites of seagrass between 1990 and 2015 15 Table 14 Information reliability scores for seagrass cover within sampling sites 17 Table 15 List of sites used in this analysis and their NRM Region 19 DEW Technical note 2018/34 v Summary This document describes the indicators, data sources, analysis methods and results used to develop this report and the associated report card. The reliability of data sources for their use in this context are also described. DEW Technical note 2018/34 vi 1 Introduction 1.1 Seagrass Seagrasses are flowering plants that grow underwater in coastal and marine environments. They evolved from land plants and adapted to marine life around 100 million years ago. Seagrasses are a valuable coastal resource, forming extensive beds or meadows comprising many individual plants. Around 40 times more animals occur in seagrass than in adjacent bare sand. They are often regarded as a marine forest and play a vital role in maintaining the marine food web and coastal stability. Eleven species of seagrasses are known to occur in South Australia covering an area of approximately 9620 km2.They are found growing on sandy or muddy bottoms in estuaries, coastal lagoons, gulfs and sheltered bays, and at the base of exposed cliffs. Seagrasses are very important sediment stabilisers and trappers but a third of seagrass meadows along the Adelaide metropolitan coast have died since 1950. Most of the seagrass has been lost within two kilometers from shore. At a distance of four kilometers offshore, seagrasses appear to be relatively healthy. Extensive offshore loss occurred around the Port Adelaide and Glenelg wastewater treatment plant sludge outfalls, but these are no longer in use. Poor water quality resulting from stormwater run-off and effluent disposal has most likely been the initial cause of seagrass loss. Once there are gaps in the seagrass meadows, the sand below the meadow edge can be eroded by waves. This is thought to have increased the rate of seagrass loss and made it difficult for plants to recolonise the seafloor, even though water quality has improved. Fine-grained sand that was once trapped by seagrass meadows has been released and washed ashore. Because the sand is fine, it accumulates in the sandbars and washes north to Largs Bay. Although in the short term this sand has added to protection of the coast, it is unsuitable for replenishing Adelaide’s beaches in the longer term. This is because it tends to remain in the underwater part of the beach and is moved too quickly by waves. As a result of the loss of sand from the seabed, the level of the seabed has steadily become up to one metre deeper and the wave energy reaching our beaches has increased. This causes a larger quantity of sand to drift north along the coast. 1.2 Environment trend and condition reporting The Minister for Environment and Water under the Natural Resources Management Act 2004 is required ‘to keep the state and condition of the natural resources of the State under review’. Environmental trend and condition report cards for South Australia are produced as a primary means for undertaking this review. Previous environmental trend and condition report card releases reported against the targets in the South Australian Natural Resources Management Plan (Government of South Australia 2012a) using the broad process outlined in the NRM State and Condition Reporting Framework (Government of South Australia 2012b). As the State NRM plan is currently under review, environmental trend and condition report cards in early 2018 will instead inform the next South Australian State of the Environment Report (SOE) due out in 2018. Again, there is a legislative driver to guide the development of SOE reporting. The Environment Protection Act 1993, which is the legislative driver to guide the development of SOE reporting, states that the SOE must: • include an assessment of the condition of the major environmental resources of South Australia 112(3(a)) • include a specific assessment of the state of the River Murray, especially taking into account the Objectives for a Healthy River Murray under the River Murray Act 2003 112(3(ab)) • identify significant trends in environmental quality based on an analysis of indicators of environmental quality 112(3(b)). DEW Technical note 2018/34 1 Environmental trend and condition report cards will be used as the primary means to address these SOE requirements. 1.2.1 Environmental trend and condition report card continual improvement Key documents guiding the content of environmental trend and condition report cards are: • Trend and Condition Report Cards Summary Paper (DEWNR 2017) • NRM State and Condition Reporting Framework (Government of South Australia 2012b). As the process by which the environmental trend and condition report cards are produced evolves, there is an increased emphasis, in keeping with the digital by default declaration, on the use of open data and reproducibility.