Monitoring Seagrass within the Reef 2050 Integrated Monitoring and Reporting Program: final report of the Seagrass Expert Group
Udy, J., Waycott, M., Carter, A., Collier, C., Kilminster, K., Rasheed, M., McKenzie, L., McMahon, K., Maxwell, P., Lawrence, E., and Honchin, C. (2019) Monitoring Seagrass within the Reef 2050 Integrated Monitoring and Reporting Program: final report of the Seagrass Expert Group. Report. Great Barrier Reef Marine Park Authority, Townsville, QLD, Australia.
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Abstract
Seagrass is widely distributed throughout the Great Barrier Reef (the Reef), with a documented 35,000 square kilometres and a potential habitat area of 228,300 square kilometres.
Seagrass meadows occur in many different environmental conditions, both within and beyond the impact of flood plumes, and are common in areas of high anthropogenic activity, such as ports and areas adjacent to urban centres.
Many processes and services that maintain the exceptional values of the Reef occur in seagrass meadows. To provide the services that support these values seagrass habitats include a range of species, growth forms and benthic landscapes, that respond to pressures in different ways. In many cases seagrasses also modify their environments to improve environmental conditions on the Reef.
Seagrasses vary spatially and temporally in their distribution and abundance across the Reef, occurring in different water quality types (estuaries, coastal, reefal and offshore) and at different water depths (intertidal, shallow subtidal, deep water). The diversity of potential seagrass habitats is one reason they support so many of the environmental services and values of the Great Barrier Reef World Heritage Area (World Heritage Area), including: habitat for crabs, prawns and fish –– supporting recreational and commercial fishing; primary food resource for species of conservation significance (dugong, green turtles, migratory shore birds); shoreline stabilisation by binding sediment to slow erosion; water clarity improvement, by promoting the settlement of fine particulate matter; and providing a natural carbon sink.
To deliver the seagrass components of the knowledge system required to deliver Reef 2050 Long-Term Sustainability Plan (Reef 2050 Plan) reporting and other management activities, there will need to be modifications and enhancements made to the current seagrass monitoring programs.
The Drivers, Pressures, State, Impact, Response (DPSIR) framework was used to facilitate the identification of linkages between the pressures on seagrass, state of the seagrass, the impact a decline in seagrass would have on community values, and the responses management agencies can take to mitigate loss of values. We have also defined twelve seagrass habitat types that occur on the Reef, identified by a matrix of water body type and water depth. The seagrasses occurring in each habitat are exposed to different pressures and require different management actions (responses) to protect and enhance the values of the community and Reef ecosystems.
The proposed monitoring program has three spatial and temporal scales, with each scale providing different information (knowledge) to support resilience-based management of the Reef. 1. Habitat assessment: will occur across the Reef at all sites where seagrass has a potential of occurring. It will determine seagrass abundance, species composition and spatial extent of each habitat type within the World Heritage Area. This scale will be focused on supporting future outlook reports, but will also provide information for operational and strategic management and contribute towards other reports. 2. Health assessment: will take place at representative regional sites, for each habitat type. These sites will provide managers with annual and seasonal trends in seagrass condition and resilience at a regional scale for each habitat. This scale will provide higher temporal detail (i.e. at least annually) of seagrass condition and resilience, supporting tactical, operational and strategic management applications. This scale will provide the majority of information for regional/catchment report cards and the assessment of management effectiveness at a catchment wide scale. It will also contribute important trends in condition and resilience to Outlook reports and other communication products with more frequent reporting. 3. Process monitoring: will take place at the fewest number of sites, nested within habitat and health assessment sites.
Due to the time-consuming and complex nature of these measurements the sampling sites will be chosen to focus on priority knowledge gaps. This scale will provide managers with information on cause-and-effect relationships and linkages between different aspects of the Reef’s processes and ecosystems. This scale will include measures of seagrass resilience (for example, feedback loops, recovery time after disturbance, history of disturbance and thresholds for exposure to pressures). The attributes measured at these sites will also provide confidence to managers regarding the impact a change in seagrass condition is likely to have on other values of the Reef (for example, fish, megafauna, coral, Indigenous heritage, and human dimensions).
To ensure that future seagrass monitoring delivers the information required to report on the Reef 2050 Plan and meets the other knowledge requirements of managers, a spatially balanced random sampling design needs to be implemented on the Reef. Existing monitoring programs can and should be integrated into this design. However, current seagrass monitoring programs do not provide a balanced assessment of seagrass condition across the entire Reef, hence are not suitable to meet the Reef 2050 Plan reporting requirements and many other management information needs.
Existing sites within current monitoring are focused on habitat types that are intertidal and shallow sub-tidal and lie close to the coast. These habitats have been previously selected because they face high levels of cumulative anthropogenic risk and therefore have higher levels of management demand for information. The current sites are likely to decline more rapidly, in response to catchment run-off and other anthropogenic pressures, than the average for seagrass meadows across the entire Reef. They also have a greater potential to show improvements from Reef catchment management actions that reduce pollution associated with run-off.
This report sets out the framework for a recommended new seagrass monitoring program, highlighting the substantial improvements in knowledge and confidence this new program will deliver, and provides a scope for the statistical design work required to support implementation of this program.
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