Beaufort (WA) Seagrass Cover 2009

Brief description

This data is part of the 2013 report "Synthesis of seagrass mapping studies conducted by the Water Science Branch of the Department of Water".

Lineage

Statement: This data was acquired by the ACEAS Seagrass Group as part of the 2013 Australia-wide risk assessment of Seagrass. Source files: WA_Beaufort_SAV_polygons.shp + WA_Beaufort_SAVsites_gda94_z50.shp Method as taken from the 2013 report "Synthesis of seagrass mapping studies" conducted by the Water Science Branch of the Department of Water": (The following methodology was adapted from the Wilson Inlet survey in 2008 conducted by Geoscience Australia with the Department of Water). Maps of submerged aquatic vegetation (predominantly seagrass) were prepared from geo-referenced underwater video data captured in each of the six estuaries in March and April 2009. Site selection in each estuary involved the preparation of a 250m by 250m grid referenced aerial image of the estuary. ‘Fixed’ sites were determined by the intersection of the easting and northing lines on the map and were evenly spaced across the extent of the estuary to optimise the area covered across the estuary. Associated with each of the fixed sites were four ‘random’ sites located North, East, South and West of each ‘fixed’ site. The distance between fixed and random sites depended on distance between fixed sites with the objective to maximise coverage between sites. The underwater video was deployed at each of the fixed and random sites in each estuary. At the fixed sites, the camera was deployed while the boat was anchored to capture precise point data that corresponded to other sediment and water quality data collected. Camera deployment at each of random sites captured data along transects, with the boat traveling into or with the prevailing winds to minimize movement of the boat and camera. Transects were between 2 and 4 minutes long and covered 50 to 100m at each of the random sites. Species composition and density (as percentage cover) were assessed in the field from the visual image obtained on the video. All transects are recorded for verification. Seagrass density changes in the estuaries were mapped by the Department of Water using ArcViewTM . Spatial Analyst was used to create the distribution map of seagrass in the Inlet by interpolating density data between the points using the inverse distance weighted method. In the absence of bathymetry data the depth limit of seagrass distribution could not be shown. In these instances seagrass distribution may be overestimated in the deeper sections of the estuary.

Notes

Credit
Department of Water, Government of Western Australia.