Fig 1.
Map of locations along the New South Wales coastline where aerial imagery was obtained to estimate P. australis declines from 2009–2014.
Map boundaries under CC Licence, originally published in 2004 by Geoscience Australia.
Fig 2.
Techniques used to classify P. australis area using aerial imagery.
The example above (A) is the most recent image from Kurnell East in Botany Bay (June 2014, [39]). An example of fragmentation is enhanced (B), showing meadow damage following the laying of submarine cables. A multi-resolution segmentation algorithm was used to segment the image into polygons based on colour and texture (C), which were then manually classified as P. australis (pale green) or ‘other’ (D). The polygons were then dissolved to represent the full area of P. australis in the image (E), which could then be formally analysed. Point sampling (F) was used to rapidly estimate percent cover of P. australis from the remaining time series imagery to determine the rate of change in meadow area. Aerial imagery reprinted under a CC BY license with permission from Nearmap, original copyright 2014.
Fig 3.
Visual representation of change in meadow area.
The image of Kurnell East in Botany Bay (June 2014, [39]) is represented by (A). Inlaid boxes (B) and (C) represent the extent of meadow area both lost and gained since April 2010. Light brown = intact meadow; dark brown = meadow area lost since 2010; pale yellow = meadow area gained since 2010. Aerial imagery reprinted under a CC BY license with permission from Nearmap, original copyright 2014.
Fig 4.
Percent change in meadow area for sites within estuaries of the Manning-Hawkesbury ecoregion from 2009–2014.
MP = Marks Point, YN = Yacht Club North, YS = Yacht Club South, BH = Barrenjoey Head, SW = Seaplane Wharf, PB = Palm Beach Ferry, MW = Manly Wharf, BG = Balgowlah, QB = Quibray Bay, KW = Kurnell West, KE = Kurnell East, DB = Dolans Bay, GB = Gunnamatta Bay, BB = Burraneer Bay.
Fig 5.
Temporal percent change in P. australis meadow cover from late 2009/early 2010 to mid-2014 in all sites within five estuaries.
Each data point represents total percent change since the initial time point. Thin-plate spline regression lines (and 95% confidence interval) are added for those sites where change was significant over the study period. YS = Yacht Club South, YN = Yacht Club North, MP = Marks Point, BH = Barrenjoey Head, PB = Palm Beach Ferry, SW = Seaplane Wharf, BG = Balgowlah, MW = Manly Wharf, KE = Kurnell East, KW = Kurnell West, QB = Quibray Bay, DB = Dolans Bay, BB = Burraneer Bay GB = Gunnamatta Bay.
Table 1.
Site locations and total change in meadow area, perimeter and patchiness from the first available image (late 2009/early 2010), until the last available image (mid-2014).
Study sites were ~520,000m2. Declines in seagrass area are highlighted in bold. (continued below).