Estimates of mangrove, coral reef and intertidal sand/mudflats
were obtained from the 2002 and 2011 1:50,000 topographic maps
published by the Singapore Armed Forces Mapping Unit. The
boundaries of each fragment of habitat were traced in ArcGis 10.0
(ESRI®, 2012) which was also used to calculate planar areas. The
original 1993 estimates by Hilton and Manning (1995) were made using the squares method, but differences between the two techniques
are likely to be minor. Areas of remaining mangroves
marked on the topographic maps include remnant patches that
once lined two estuaries along the northern coastline, both of
which have now been converted into freshwater reservoirs. These
remnants are no longer connected to the marine environment, and
were therefore not calculated within the total area of mangroves.
On the other hand, some fragments not recorded in the topographic
maps were included based on a contemporary publication by Yee
et al. (2010) which documented the extent of mangroves in 2010.
Accessible areas were ground-truthed by the first author to confirm
their presence in 2013. Our estimates of the intertidal coral reef and
sand/mudflat areas were based solely on the topographic maps. The
coral reef areas marked out on the topographic maps used here
represented intertidal reef flats only. The sub-tidal reef slopes were
excluded, as they were in Hilton and Manning (1995).