Wilson Inlet (WA) Seagrass 2007

Brief description

Aquatic flora surveys were conducted in Wilson Inlet in 2007 and 2008. This data is part of the 2013 report "Synthesis of seagrass mapping studies" conducted by the Water Science Branch of the Department of Water. The 2007 survey was conducted to review any changes in seagrass distribution since the previous survey in 1996 (data not included in this record), and was funded internally by the Water Science branch. The 2008 survey was conducted by the WA Department of Water together with Geoscience Australia. The objective of the 2008 survey was to collect baseline data on seagrass composition and distribution in key estuaries of southern and south-western WA. This data was acquired by the ACEAS Seagrass Group as part of the 2013 Australia-wide risk assessment of Seagrass. Surveys were conducted again in December 2017, April 2018, December 2019, December 2020, December 2021 and December 2022 by the Department of Water and Environmental Regulation as "Wilson Inlet Seagrass Survey". The datasets making up the 2007-2008 Wilson Inlet seagrass survey data are: WA_WilsonInlet_seagrass_polygons - polygon dataset showing interpolated percentage cover of seagrass with species information (where available). This record provides access to the initial WA DoW surveys. See associated DWER records in Data WA catalogue for access to newer surveys at this site.

Lineage

Maintenance and Update Frequency: notPlanned

Statement: ---2007 survey-- The 2007 Wilson Inlet seagrass survey was conducted by snorkel tows along predetermined transects in the estuary. The transects were 200-300 m apart running perpendicular to the shoreline to the edge of the seagrass meadow (usually ending before the 3m depth limit). Coordinates were recorded along each transect together with percentage cover classes of seagrass. Seagrass density changes in Wilson inlet were mapped using ArcView. 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. Given the basin type nature of the Inlet a cut-off boundary of seagrass was assumed using the 2 meter contour line of the Wilson Inlet bathymetry layer. Two meters was the reported depth limit of seagrass in the Inlet. This showed the central part of the basin to have no seagrass. ---2008 survey--- The 2008 survey was completed in November/December 2008 as a component of a Masters project by Maggie Tran with Geoscience Australia. The main objective of this survey was to characterise the benthos, of which submerged aquatic vegetation (seagrass) was a component/category. Assistance with seagrass identification and classification was provided by the Department of Water. Sites were preselected in a grid arrangement over the whole extent of the estuary. Three random sites North, East and South of the site were also surveyed. The distance between fixed and random sites was variable. Underwater video was deployed at each of the fixed and random sites in each estuary. Camera deployment at each of the 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 along with other substrate categorization. All video transects were recorded for verification. Seagrass density changes in Wilson inlet were mapped by the Department of Water using ArcView. 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. Given the basin type nature of the Inlet a cut-off boundary of seagrass was assumed as the maximum depth at which seagrass was recorded in the survey (3 m). This showed the central part of the basin to have no seagrass.

Notes

Credit
Department of Water, Government of Western Australia.