The distribution and protection of intertidal habitats in Australia
Kiran L. Dhanjal-Adams
, Jeffrey O. Hanson
, Nicholas J. Murray
, Stuart R. Phinn
Vladimir R. Wingate
, Karen Mustin
, Jasmine R. Lee
, James R. Allan
Jessica L. Cappadonna
, Colin E. Studds
, Robert S. Clemens
, Chris M. Roelfsema
and Richard A. Fuller
School of Biological Sciences, University of Queensland, Brisbane, Qld 4072, Australia.
Centre for Ecosystem Science, School of Biological, Earth and Environmental Sciences,
University of New South Wales, Sydney, NSW 2052, Australia.
School of Geography, Planning and Environmental Management, University of Queensland,
Brisbane, Qld 4072, Australia.
Department of Environmental Science, University of Basel, Basel 4056, Switzerland.
Department of Geography and Environmental Systems, University of Maryland Baltimore County,
Baltimore, MD 21250, USA.
Corresponding author. Email: firstname.lastname@example.org
Abstract. Shorebirds have declined severely across the East Asian–Australasian Flyway. Many species rely on intertidal
habitats for foraging, yet the distribution and conservation status of these habitats across Australia remain poorly understood.
Here, we utilised freely available satellite imagery to produce the ﬁrst map of intertidal habitats across Australia. We
estimated a minimum intertidal area of 9856 km
, with Queensland and Western Australia supporting the largest areas.
Thirty-nine percent of intertidal habitats were protected in Australia, with some primarily within marine protected areas
(e.g. Queensland) and others within terrestrial protected areas (e.g. Victoria). Three percent of all intertidal habitats were
protected by both marine and terrestrial protected areas. To achieve conservation targets, protected area boundaries must
align more accurately with intertidal habitats. Shorebirds use intertidal areas to forage and supratidal areas to roost, so a
coordinated management approach is required to account for movement of birds between terrestrial and marine habitats.
Ultimately, shorebird declines are occurring despite high levels of habitat protection in Australia. There is a need for a
concerted effort both nationally and internationally to map and understand how intertidal habitats are changing, and how
habitat conservation can be implemented more effectively.
Received 29 April 2015, accepted 24 December 2015, published online 10 March 2016
Migratory shorebird populations are declining rapidly across
continental Australia (Clemens et al.2016), and also locally in
many places including Tasmania (Cooper et al.2012; Reid and
Park 2003), South Australia (Close 2008; Paton et al.2009),
Victoria (Minton et al.2012; Rogers and Gosbell 2006), the east
of the country (Nebel et al.2008; Wilson et al.2011) and in
Western Australia (Creed and Bailey 2009; Rogers et al.2011).
Based on the severity of their declines and a high likelihood
that threatening processes are continuing, both Eastern Curlew
(Numenius madagascariensis) and Curlew Sandpiper (Calidris
ferruginea) were recently up-listed to Critically Endangered
under the Environment Protection and Biodiversity Conservation
Act 1999 (EPBC Act; Department of the Environment 2015a,
2015b). At a broader scale, similar declines have also been
reported across the East Asian–Australasian Flyway (EAAF;
Amano et al.2010). This is particularly troubling as not only
does the EAAF have the greatest number of threatened species
and the largest number of shorebird populations among the
world’sﬂyways, it also has the least information on conservation
status (Amano et al.2010; International Wader Study Group
2003; Wilson et al.2011). Therefore, the EAAF is arguably the
ﬂyway in greatest need of conservation evaluation and action
(Amano et al.2010).
The majority of migratory shorebirds rely on intertidal habitats
for foraging (Galbraith et al.2002), deﬁned here as the area
between the high and low waterline (Murray et al.2012). Long
distance migrations are energetically demanding (Blem 1990),
and shorebirds must feed rapidly and store fat reserves before,
during and after migration to ensure survival and reproduction
(Drent and Piersma 1990). Relative to other habitat types, inter-
tidal habitats are limited to a narrow strip along the coastline,
leaving the species these habitats support vulnerable to extinction
(Lee and Jetz 2011; Purvis et al.2000). For migratory shorebirds,
the likelihood that a particular site will sustain large numbers of
birds is strongly correlated with the area of available intertidal
habitat, a key factor inﬂuencing the availability of benthic prey
organisms (Evans and Dugan 1983; Galbraith et al.2002). Loss
Journal compilation BirdLife Australia 2016 www.publish.csiro.au/journals/emu
of intertidal habitats could reduce the carrying capacity of a site,
decreasing the number of birds in an area and increasing the
risk of local extinctions (Iwamura et al.2013; Sheehy et al.2011;
Sutherland and Anderson 1993).
Currently, migratory shorebirds are considered a matter of
national environmental signiﬁcance under the EPBC Act, owing
to their inclusion in bilateral migratory bird agreements with
China, Japan, and the Republic of Korea. Any development or
activity likely to cause signiﬁcant impact must be assessed under
the EPBC Act (Department of the Environment 2013), where the
concept of ‘important habitats’plays a crucial role in protecting
shorebirds. Important habitats in Australia for migratory shore-
birds under the EPBC Act include those recognised as nationally
or internationally important, based on criteria adopted under the
Ramsar Convention on Wetlands (1971, available at http://www.
pdf, accessed 4 February 2016). According to this convention,
wetland habitats should be considered internationally important
if they regularly support 1% of the individuals in a population, or
a minimum of 20 000 individuals of all species combined. Na-
tionally important habitats can be deﬁned using a similar approach
if they regularly support 0.1% of the EAAF population of a single
species, 2000 migratory shorebirds, or 15 migratory shorebird
species (Clemens et al.2010). However,with no formal evaluation
of the distribution and protection of intertidal habitats in Australia,
it remains difﬁcult to assess how well such criteria are performing.
Mapping the occurrence and protection of intertidal habitats
is critical given their restricted distribution and importance to
migratory shorebirds. Indeed, formal evaluation of the distribu-
tion and extent of intertidal habitats will provide valuable data to
help assess the impact of alternative coastal development plans on
shorebird populations. Conserving intertidal habitats requires an
understanding of habitat distribution, as well as extent and current
levels of protection by both marine and terrestrial protected areas.
However, mapping intertidal habitats can be complicated using
any form of ﬁeld survey, airborne or satellite remote sensing, as
the waterline is highly dynamic, inundating the habitat once or
twice per day and exposing it to a varying extent. Although many
habitats have been effectively mapped in Australia, the distribu-
tion and status of intertidal habitats at a national scale, aside from
mangroves and saltmarsh, remain unknown below a resolution of
accessed 20 January 2016).
Recent advances in the availability of satellite image archives
and multi-temporal image analysis techniques have led to the
development of a method for mapping the distribution of inter-
tidal habitats at continental scales (Murray et al.2012). This has
paved the way for a regional status assessment of tidal ﬂat habitats
in the Yellow Sea (Murray et al.2014; Murray et al.2015).
Murray et al.(2014) demonstrated that intertidal habitats in the
Yellow Sea have declined by 65% in the last ﬁve decades, and by
28% since the 1980s. However, there is little information on
the extent of intertidal habitats outside the Yellow Sea. Here, we
use the methodology developed by Murray et al.(2012) to create
the ﬁrst map of intertidal habitats for Australia, and assess the
extent to which intertidal habitats are protected by marine and
terrestrial protected areas. This mapping (i) enables a better
understanding of the distribution and protection of intertidal
habitats in Australia, (ii) forms an exemplar for the development
of continent wide tidal ﬂat maps in other parts of the world, and
ﬁnally (iii) helps identify critical shorebird habitat at a national
The method we used to map the extent and distribution of
intertidal habitats in Australia was based on a continental-scale
mapping project conducted across Asia by Murray et al.(2012,
2014). We ﬁrst obtained the complete metadata of the freely
available Landsat Archive from USGS Earth Explorer (http://
earthexplorer.usgs.gov, accessed 20 January 2016). We con-
strained our analysis to the years spanning 1999–2014, to max-
imise coverage and permit the identiﬁcation of images acquired
at low tidal elevations (see Fig. S1, available online as supple-
mentary material). We identiﬁed all Landsat images that inter-
sected the Australian coastline. Using the Tide Model Driver
(TMD) Matlab toolbox for tide modelling, we estimated the tidal
elevation at the time of image acquisition with the Indian Ocean,
Tasmania, and Northern Australia tide models available from the
Oregon State University suite of tide models (Egbert and Ero-
feeva 2002; Padman and Erofeeva 2005). Images acquired within
the upper and lower 10% of the tidal range were downloaded and
visually reviewed before being selected for the ﬁnal remote
sensing analysis. For Landsat images not available via Earth
Explorer, due to extensive cloud cover or other problems, we
obtained the ortho-corrected Landsat Archive images from Geo-
science Australia and the Department of Environmental Resource
Management (Filmer et al.2010). Image pre-processing, sorting
and pairing for intertidal mapping, followed the procedure in
Murray et al.(2012).
The ﬁnal image set consisted of 99 pairs of Landsat scenes
over 79 path-row footprints of 185 km 170 km each, with 170
Enhanced Thematic Mapper Plus (ETM+), and 28 Landsat
Thematic Mapper (TM) satellite images (Fig. S1). The mean
difference in acquisition time between high and low tide image
pairs was 1.49 1.18 years. The Normalised Differenced Water
Index (NDWI; McFeeters 1996) and, where possible, the Mod-
iﬁed Normalised Differenced Water Index (MNDWI; Xu 2006)
were calculated for each pixel to maximise the likelihood of
differentiating between water and non-water areas, irrespective of
the substrate or benthos (McFeeters 1996;Xu2006). Each image
was then classiﬁed into a binary land/water image by manually
assigning a threshold that most effectively identiﬁed the waterline
in each image. Images were discarded if a suitable threshold could
not be found that consistently identiﬁed the waterline throughout
the image. The classiﬁed high and low tide images in each pair
were then differenced, resulting in a delineation of intertidal
habitats as the difference between the two input images (Murray
et al.2012). For further detail on the NDWI differencing method
refer to Murray et al.(2012).
The intertidal areas identiﬁed from all Landsat images were
merged to create the ﬁrst estimate of the intertidal habitat distri-
bution across Australia at a 30 m resolution (full dataset can be
found in Dhanjal-Adams et al.2015). Post-processing was
necessary to remove incorrectly classiﬁed pixels (Murray et al.
2012; Murray et al.2014). False positive classiﬁcation errors
occurred both landward and seaward in many images. In part,
these were due to seasonal changes in water presence, such as
BEmu K. L. Khanjal-Adams et al.
ﬂooding and inland ephemeral wetlands inland appearing in one
image but not the other, but most errors occurred when ocean was
classiﬁed as intertidal. Such errors resulted from cloud cover,
water turbidity, algal blooms and whitewash from waves being
classiﬁed as land, thus affecting the classiﬁcation output. Such
limitations are inherent in delimiting tidal ﬂat and open water
features, but are easily corrected during post-processing (Liu et al.
2012; McFeeters 1996; Ryu et al.2002;Xu2006).
We completed an accuracy assessment on the ﬁnal intertidal
habitat map to measure classiﬁcation error, by comparing the
mapped dataset with a reference set using a confusion matrix
(Congalton and Green 2008; Roelfsema and Phinn 2013). Using
stratiﬁed random sampling, we generated 204 sample locations
within 10 km of the coastline and within intertidal habitats. Each
point was assessed by an independent reviewer and labelled as
belonging to one of the two classes (‘intertidal’or ‘other’)to
create a reference dataset based on a combination of ground-truth
information, including low tide Landsat imagery, Google Earth
imagery and Esri imagery. For each point, the mapped data were
extracted from the intertidal habitat map created in this study.
Then, using the mapped data and the reference dataset, we
populated a confusion matrix (Fig. S2) and quantiﬁed the map
category, user’s and producer’s accuracy, as well as the map
overall accuracy (Congalton and Green 2008).
User’s accuracy represents the probability that a pixel on the
map is correctly classiﬁed as intertidal. Producer’s accuracy
represents a measure of omission error, i.e. the probability a pixel
was missed by the classiﬁcation (Congalton and Green 2008).
Individual user’s accuracy for the intertidal class was 100% and
for the other class was 91.2% (Fig. S2), i.e. all the pixels in the
intertidal class were intertidal, but some pixels in the other class
were also intertidal. The producer’s accuracy for the intertidal
class was 91.9%, and for the other class was 100% (Fig. S2), i.e.
some intertidal habitats were found in the ocean class, while no
ocean was found in the intertidal class. This resulted in an overall
accuracy of 95.6%, which is well above the commonly cited
acceptable Landsat scale mapping accuracy level of 85% (Con-
galton and Green 2008; Foody 2009). These small errors highlight
false negative classiﬁcation errors, where not all intertidal habitats
were picked up during the mapping process. These errors were,
in part, due to striping on Landsat ETM+ imagery as a result of
a sensor malfunction after May 2003, causing some images to
miss 22% data. We applied the standard approach used to
minimise striping, by merging 15 years of classiﬁcation maps
together (Markham et al.2004). False negative classiﬁcation
errors (omission errors) were also, in part, due to the image
selection process. To maximise the number of images used in
the analysis with the aim of maximising coverage, we used images
taken within 10% of the high and low tide, not the highest or
lowest possible tides. Therefore, small strips of intertidal habitats
were missing on the landward and seaward sides of the correctly
mapped intertidal habitats. Although we used highly accurate tide
models, errors were likely to remain in the tide predictions due
to tidal variation across the extent of each Landsat image, as
well as variability in timing of Landsat imagery. By combining
multiple images, these errors were again minimised. For further
discussion of errors associated with this remote sensing method,
refer to Murray et al.(2012).
Finally, to determine the level of protection of mapped
intertidal habitat, we acquired data from the Collaborative Aus-
tralian Protected Area Database (CAPAD) for 2014 (http://www.
environment.gov.au/land/nrs/science/capad/2014, accessed 20
January 2016) and estimated the area of intertidal habitats
protected by marine protected areas, terrestrial protected areas,
Our map of the intertidal habitats of Australia achieved 91%
coverage of the Australian coastline with an overall classiﬁcation
accuracy of 95.6% at a 30 m resolution (Table 1; Fig. S2).
However, 9% of the coastline remained unmapped particularly
in Western Australia (Fig. 1). Roebuck Bay for example, an
internationally and nationally important shorebird site was not
mapped due to a lack of good quality images of the area.
We identiﬁed a minimum total of 9856 km
habitat across Australia (Figs 1and 2; Table 1). The states with
the largest areas of intertidal habitat were, in decreasing order,
Queensland, Western Australia, Northern Territory and South
Australia with >0.2 km
per mapped kilometre of coastline
(Table 1; Fig. 1). Intertidal habitats were largely concentrated in
estuaries, embayed coastlines and areas protected by coral reefs
(Figs 1and 2).
Intertidal habitats were generally very well covered by pro-
tected areas, with 39% of all intertidal habitats across Australia
overlapping marine or terrestrial protected areas (Table 1; Fig. 2).
The Northern Territory had the lowest level of protection at 6%
and Victoria the highest at 80% (Table 1). There was marked
Table 1. Distribution and protection of mapped intertidal habitats in Australia. PA, Protected Area
State Mapped coastline
in km (Percentage
of total coastline)
habitat in km
Area of intertidal
habitat per km
Total PA in km
(Percentage of total
Marine PA only
of total PA)
only in km
of total PA)
terrestrial PA in
of total PA)
NSW 3793 (100.00) 95.6 0.03 47.6 (49.7) 27.5 (58.0) 17.7 (35.1) 3.3 (6.9)
NT 10 384 (96.68) 2235.1 0.22 129.5 (5.8) 24.3 (18.8) 105.2 (81.2) 0.0 (0.0)
Qld 11 235 (97.54) 2682.1 0.24 1608.6 (60.0) 1513.4 (94.1) 73.0 (4.5) 22.2 (1.4)
SA 4709 (99.99) 925.8 0.20 616.1 (66.5) 530.5 (86.1) 20.3 (3.3) 65.2 (10.6)
Tas 4235 (87.10) 91.8 0.02 47.5 (51.7) 8.2 (17.3) 39.3 (82.7) 0.0 (0.0)
Vic 2404 (99.99) 231.7 0.10 185.6 (80.1) 0.0 (0.0) 185.6 (100.0) 0.0 (0.0)
WA 15 611 (80.15) 3593.4 0.23 1226.1 (34.1) 659.6 (53.8) 555.1 (45.3) 11.3 (0.9)
Australia 52 372 (91.08) 9855.6 0.19 3860.9 (39.2) 2763.8 (71.6) 995.3 (25.8) 101.9 (2.6)
Intertidal habitats in Australia Emu C
variation in whether intertidal habitats were primarily represented
in marine or terrestrial protected areas. For example, of the
protected intertidal habitat in Queensland, 96% occurred
exclusively within marine protected areas. Yet in Victoria, only
terrestrial protected areas covered intertidal habitat (Table 1;
Fig. 2). Furthermore, 3% of protected intertidal habitats in
Australia were covered by both marine and terrestrial protected
areas, with up to 11% overlap between marine and terrestrial
protected areas in South Australia (Table 1; Fig. 2).
We present the ﬁrst high spatial resolution map of intertidal
habitats in Australia, determining that intertidal habitats have a
minimum total area in Australia of 9856 km
(Table 1; Figs 1and
2). About 39% of the total extent of intertidal habitat is covered
by protected areas (Table 1; Fig. 2), suggesting these habitats are
well represented within the Australian protected area network.
This information is crucial for assessing how Australia’s coastal
protected area networks are contributing towards global targets
such as Aichi Target 11, laid out under Goal C of the Strategic Plan
for Biodiversity (https://www.cbd.int/sp/, accessed 20 January
2016) suggesting that 10% of coastal and marine environments
be protected by 2020.
We discovered large differences in the extent to which inter-
tidal habitats are protected among states, with some states pro-
tecting over 60% of their intertidal area (Victoria, South Australia
and Queensland), and others less than 6% (Northern Territory;
Table 1; Fig. 2). The lowest levels of protection however occurred
in the Northern Territory, where some of the largest numbers of
shorebirds (Chatto 2003; Clemens et al.2016) and largest areas of
intertidal habitats (0.22 km
/km mapped coastline; Table 1) were
observed. The Northern Territory is however aiming to increase
the exploitation of energy and mineral resources (Northern
Territory Government 2013), and low levels of protection could
be detrimental to already declining shorebird populations
if development is not planned strategically.
Variations between states probably highlight differences in
protected area designation and management, potentially as a
result of the socio-political context. Queensland, for instance,
has particularly high levels of protection as a result of the Great
Barrier Reef being designated as a United Nations Educational,
120°0'0"E110°0'0"E 130°0'0"E 140°0'0"E 150°0'0"E 160°0'0"E
120°0'0"E 130°0'0"E 140°0'0"E 150°0'0"E
Area of intertidal habitat in square kilometres
Landsat footprint 0 280 560 1120 km
Fig. 1. Net area of intertidal habitats across Australia mapped at a 14 km grid resolution. (For colour ﬁgure, see online version
available at http://www.publish.csiro.au/nid/17.htm.)
DEmu K. L. Khanjal-Adams et al.
Scientiﬁc and Cultural Organization (UNESCO) World Heritage
Site. However, it is unclear how such designations can beneﬁt
shorebirds when they are not speciﬁcally targeted at shorebird
Some intertidal habitats were primarily managed as part of a
marine protected area, while others as part of a terrestrial protected
area (Table 1; Fig. 2). There is a clear potential for such differ-
ences to lead to inadequate management, as terrestrial protected
areas might not always prioritise their marine environments
and marine parks might underplay the importance of supratidal
habitats that function as shorebird breeding or roosting sites
(Department of Environment Water and Natural Resources
2014; Department of National Parks Recreation Sport and Racing
2014; Department of Parks and Wildlife 2014; Department of
Primary Industries Parks Water and Environment 2014;Ofﬁce of
Environment and Heritage 2014; Parks and Wildlife Commission
of the Northern Territory 2014; Parks Victoria 2014). Further-
more, some intertidal habitats are managed under both marine
and terrestrial protected area designations (Table 1; Fig. 2). In
Australia, this occurs for 3% of all protected intertidal habitats.
In South Australia in particular, where there are large areas of
intertidal habitats (0.20 km
per km of coastline mapped; Table 1),
10% fall under the jurisdiction of both terrestrial and marine
protected areas. Such overlap could lead to confusion, with
neither management agency taking full responsibility for the
conservation of intertidal habitats and the shorebirds reliant on
them. Alternatively, overlap has the potential to lead to better
protection when both agencies manage intertidal habitats togeth-
er. Indeed, shorebirds move between intertidal habitats to forage
and inland wetlands to roost, so combined management of
terrestrial and marine environments will be critical for ensuring
healthy shorebird populations. There is a strong need for sus-
tained collaboration between terrestrial and marine protected area
managers, as well as other stakeholders, to ensure that protected
area boundaries align more sensibly with intertidal habitats to
beneﬁt shorebirds. Accurate, spatially comprehensive maps de-
rived from satellite imagery such as ours are therefore important
for identifying habitat, delineating protected area boundaries,
and facilitating targeted management of migratory shorebirds in
Shorebirds congregate in large numbers in roost sites, which
can be readily identiﬁed as important habitat under the EPBC Act,
but disperse during feeding. Densities while foraging in intertidal
areas are typically far lower, making it more difﬁcult to delineate
important habitat, because the birds rarely concentrate in sufﬁ-
ciently large numbers to trigger the criteria. Such conservation
criteria are therefore often inappropriate for protecting intertidal
habitats from developments, despite their importance to shore-
120°0'0"E 130°0'0"E 140°0'0"E 150°0'0"E
120°0'0"E110°0'0"E 130°0'0"E 140°0'0"E 150°0'0"E 160°0'0"E
0 285 570 1140 km
Terrestrial and marine PA
Primary source of protection
Fig. 2. Primary source of protection of intertidal habitats across Australia mapped at a 14 km grid resolution. PA, Protected Area.
Intertidal habitats in Australia Emu E
birds. In such cases, determination of important habitat could
usefully occur at a broader scale, for example with all intertidal
habitats within an important estuarine system being classiﬁed as
important habitat. Not all shorebirds rely on intertidal habitats,
and such criteria also apply to supra-tidal habitats, including
saltworks and ephemeral wetlands, which are critically important
for shorebirds in Australia. Intertidal habitat usage both inside
and outside of protected areas needs to be formally assessed for
all nationally important shorebird species, as not all intertidal
habitats are used equally by different species. Finally, greater
understanding of how protected areas are designated and regu-
lated is needed, and how these vary between states is an important
step towards coordinating management at the national scale.
Ultimately, protection of intertidal habitats across Australia
remains essential to the long-term conservation of EAAF shore-
bird species. However, shorebirds are declining across Australia
despite the apparent high level of protection of intertidal habitats
(Clemens et al.2016). There is mounting evidence that these
declines are driven by loss of intertidal habitats from migratory
stop-over sites outside Australia, such as the Yellow Sea (Ma et al.
2014; MacKinnon et al.2012; Moores et al.2008; Murray et al.
2014). Any threat impacting such restricted habitats, particularly
in stop-over sites, is likely to have a disproportionate effect on
abundance (Iwamura et al.2013; Sheehy et al.2011; Sutherland
and Anderson 1993). Mapping of the Yellow Sea, for example,
has already revealed declines of 65% in extent of tidal ﬂats in
the last ﬁve decades (Murray et al. 2014). It remains unclear to
what degree these changes in habitat availability are being
mirrored throughout the EAAF. Mapping of intertidal habitats
is urgently needed across the entire ﬂyway to inform coordinated
protection of shorebirds and to identify population bottlenecks
during migration. Well managed and well connected intertidal
habitats across the ﬂyway are essential if we are to prevent further
migratory shorebird extinctions within our lifetimes.
We thank Tony Gill and staff from the Joint Remote Sensing Research
Program for their time, expertise, and access to data and computer processing
systems. Landsat data are freely available from the United States Geological
Survey and pre-processed and ortho-rectiﬁed Landsat images were provided
by Geoscience Australia and the Department for Environmental Resource
Management. We also thank Amelie Corriveau, Maggie McKeown and
Madeleine Stigner for their involvement in the mapping component of the
project. This project was supported by project CA130019 of the Gladstone
Ports Corporation Limited, and an Australian Research Council Linkage
Grant LP150101059, co-funded by the Burnett-Mary Regional Group, the
Queensland Department of Environment and Heritage Protection, and
the Queensland Wader Study Group. Additional support was provided by
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