A framework for defining seagrass habitat for the Great Barrier Reef, Australia

This report describes a framework to define seagrass habitat and seagrass desired state for the Great Barrier Reef (GBR). We developed this by defining assessment zones using key physical attributes for the GBR. The assessment zones were developed with two main objectives: (1) to assess the representativeness of existing seagrass data throughout the GBR; and (2) to provide a framework in which to develop seagrass desired state (i.e. condition targets). We defined assessment zones using spatial data that reflect environmental and benthic condition likely to affect seagrass distribution, diversity and density. These include: (1) latitude, defined as regions using 6 Natural Resource Management (NRM) boundaries, (2) influence from and proximity to land (estuarine, coastal, reef, and offshore water bodies), and (3) water depth (intertidal, shallow subtidal <10m, and deep subtidal >10m) resulting in 68 zones for the GBR. The largest assessment zone was the offshore water body in every region. Deep subtidal was the largest depth zone in coastal, reef, and offshore waters in each region. The estuarine deep subtidal zone was limited. Zones are seagrass-centric and not analogous to the Great Barrier Reef Marine Park zoning. Data from extensive seagrass surveys and long-term monitoring across the GBR since the early 1980s provides information on seagrass presence/absence, species composition, abundance, and spatial extent. Data rich areas include coastal and estuarine intertidal and shallow subtidal zones. Data from reef and offshore zones, and in deep subtidal zones, are more limited as it comes from sporadic one-off surveys and few meadows have been mapped. Available seagrass data ranges from sporadic large-scale survey data with low to medium spatial and low temporal resolution, to high spatial and high temporal resolution data collected seasonally at discrete sites. Defining these assessment zones is a critical first step in defining habitat types and quantifying desired state for GBR seagrasses. Habitat attributes not included in the zones, such as sediment type and exposure to wind and waves, as well as new seagrass biomass data will be used to update the framework, turning it into a full habitat assessment for defining desired state. A case study based in Cleveland Bay, as well as previous research, will be used to identify how this framework will be updated. Seagrass desired state is an ecological target that can be used to assess the effectiveness of management strategies to protect seagrass of the GBR. Desired state analysis requires data with medium to high spatial and temporal resolution that allows assessment in the context of disturbance events, recovery trajectories, and seasonal fluctuations. Robust analysis will be restricted to locations within zones where continuous data collection has occurred, e.g. the Marine Monitoring Program (MMP) and Queensland Ports Seagrass Monitoring Program (QPSMP), and for an adequate time span (generally >10 years).

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978-1-925514-32-2

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