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3.2 MANDURAH
Long Island (Creery Wetlands), Florida Beach (a degraded urban
coastal strip) and Seal Rock (Yalgorup National Park)
Regional setting of the Mandurah transects
Mandurah (that is virtually a southern suburb of Perth following recent urban sprawl) is located in the
Drummond Botanical Subdistrict (Beard 1980) or the Swan Coastal Plain Biogeographical Region (IBRA,
2000). It has a climate that can be classified as sub-humid (Gentilli 1972). Mean annual rainfall is about
875 mm (Australian Bureau of Meteorology, 2005) with a mean annual evaporation of about 1750 mm.
Winter rain is generally reliable with a growing season of about six months. In summer, there is a pattern
of moderate winds from the SE to NE in the morning and strong afternoon winds from the SW
(occasionally to 40 km/hr). In winter the winds are generally SW to NW due to the shift north of the
cyclone –anticyclone system (Gentilli 1972).
The Swan Coastal Plain is a region of deep sedimentary materials (Playford et al., 1976) with landforms on
a regional scale generally being dominated by a series of shore-parallel dune systems. At the coast, the
Holocene Quindalup Dunes comprise the more recent landforms and these often override the Pleistocene
Spearwood Dunes further inland. Landforms of these two dune systems typify the coastal area south of
Mandurah (including the Yalgorup National Park and most of the Peel–Harvey Inlet). A definitive account
of the paleogeography of the Yalgorup area (including the description of the landforms, Pleistocene
stratigraphy and the time sequence of the formation of the various units) is provided in Semeniuk (1997).
The limestone forming the hinterland of the Seal Rock transect is the Tim’s Thicket Limestone
stratigraphic unit characterized by Semeniuk (1997) and this unit is the oldest limestone of the Yalgorup
area. This limestone outcrops more closely to the beach in the Tim’s Thicket to Seal Rock area than further
south. Between the Tim’s Thicket Limestone hinterland and the beach in this area, there is a narrow band
(mostly less than about 200m wide) of shore-parallel Holocene sand dunes. The Bouvard Reefs (offshore)
are another Pleistocene limestone unit of the area and although now largely submarine, they provide a
degree of shelter to the beaches in the Tim’s Ticket area including the beach at Seal Rock.
The coastal landforms and peripheral wetlands of the Peel-Harvey estuary (just south of the town of
Mandurah) were characterized by Semeniuk & Semeniuk (1990). The Peel– Harvey estuary (including the
Creery Wetlands) was subsequently listed in the Ramsar List of Wetlands of International Significance
(Ramsar, 2004). The Peel Inlet (in the north of this estuarine system) is a roughly circular receiving basin
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for the Murray and Serpentine Rivers and is barred from the Indian Ocean to the west by a barrier ridge
of Spearwood Dunes (except for an artificial channel excavated through the ridge at Dawesville in 1995).
In the south-west, the Peel Inlet is connected to the Harvey Inlet that receives the Harvey River via an
elongate fluvial delta. In the north of the Peel Inlet, there is a tidal delta and shoal complex with a narrow
natural exchange channel leading to the ocean. Other peripheral landforms of the Peel Inlet include a
stranded shoal complex and a relict tidal delta at the northern exchange channel, a spit-lagoon complex in
the north east of the inlet and an extensive beach ridge complex on the eastern shores of the inlet. The Peel
Inlet is subject to wind waves and wind-induced currents, oceanic wave action and tidal exchange. These
processes result in the influx and mixing of waters and the transport and deposition of sediments and
nutrients. The complexity of the resulting landforms of the Peel-Harvey estuarine system underlies a varied
mosaic of peripheral wetland type present and thus complex small-scale vegetation patterns. Unfortunately
many of the original landforms have recently been decimated by canal developments. The artificial
channel connecting the Peel Inlet to the ocean was excavated in 1995 at Dawesville in an attempt to flush
the inlet of its high anthropogenic nutrient load. The development and disturbance of the extensive
peripheral wetlands of the Peel-Harvey estuary have been accompanied by serious environmental and
social problems including acidification due to disturbance of acid sulphate soils and the high prevalence of
mosquito-borne Ross River Virus. In addition the Dawesville Cut has had a profound influence on the
hydrodynamics and water chemistry of the Peel – Harvey Inlet by increasing exchange of the waters of the
inlet with the ocean thus magnifying tidal effects and changing the inlet from seasonally fresh to brackish
system to a predominantly marine salinity system.
Landforms and sediments of the Mandurah transects
The surface sediments in the Mandurah SWALE 2 transects (Table 8) were mainly medium creamcoloured carbonate and quartz sands. There was also estuarine, shelly mud flanking the deltaic shoals in
the Creery Wetlands. In the dampland behind the foredune of the Seal Rock transect, the sand was more
coarse and consisted of humic grey quartz and carbonate grains.
The coastal reserve fronting the new suburb of Florida Beach was highly modified by earthworks
associated with the development. Originally the landforms were dominated by a large blowout. The first
line of houses was built behind a tall retaining wall (leaving only a minimum setback from the beach) and
a golfcourse was later installed just north of the housing with turf being laid within 100m of the ocean.
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At the Creery Wetlands, Creery Island (also known as Long Island) is one of the shoals of the active
tidal delta at the southern end of the natural exchange channel in the north of Peel Inlet. It is an east-west
oriented sand bar (and thus almost at a right angle to the north-south axis of the channel) that is flanked to
the north and south by extensive estuarine tidal flats of shelly, grey mud.
In the Yalgorup National Park (south of Tim’s Thicket) the landscape is characterized by Holocene-age
calcareous dunes over limestone that outcrops as a low tidal platform and as large rocks (such as the
distinctive cylindrical-shaped Seal Rock) on the beach. The local dunes are of moderate height and not
extensive as they are generally truncated by a low plateau of Tim's Thicket Limestone less than 200 m
inland. The foredune in the vicinity of the Seal Rock transect (about 20 m in height at its crest) is typical of
the area and includes a shore-normal parabolic dune blowout truncated inland by the limestone plateau.
Just north of the blowout, extending from the leeside of the foredune to several hundred meters inland
there is also a parabolic shore-normal valley in the low limestone plateau. The shallowly-concave floor of
this valley lies close to sea level and is seasonally waterlogged. This landform can be categorized as a
dampland.
Table 8: Mandurah transect surface sediments
Soil sample site : Transect
and landform
Dominant vegetation
Creery wetlands seaward
margin of sand spit
Sarcocornia quinqueflora and
Juncus kraussi sedges with
tall open shrubs of Melaleuca
cuticularis
Low open woodland of
Casuarina obesa over grasses
flanked by the sedges Juncus
kraussii, Ficinia nodosa, &
Bolboschoenus caldwellii.
Halosarcia indica &
Halosarcia halocnemoides
low heath with herbs
Grey sandy carbonate mud
Florida Beach foredune
Spinifex hirsutus grassland
with sparse herbs
Cream medium carbonate and
quartz sand.
Seal Rock foredune
Leucophyta brownii, Olearia
axillaris, Alyxia buxifolia and
Diplolaena dampierii heath.
Melaleuca huegelii closed
scrub over herbland
Melaleuca viminea closed
scrub to low open shrubs over
sedges Baumea juncea,
Juncus kraussii, Gahnia
trifida.
Medium cream-coloured carbonate
and quartz sand.
Creery wetlands low
crested sand spit
Creery wetlands high
tidal flat
Seal Rock gentle slope
leeward of the foredune
Seal Rock dampland
Sediment description
Cream-coloured medium to fine
quartz and carbonate sand
Grey carbonate mud
Medium to coarse grey quartz and
carbonate sand
Medium to coarse grey humic
quartz and carbonate sand
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Vegetation and flora of the Mandurah transects
1. Creery Island, Creery Wetlands
The seaward slope of the low dune along the south shore of Creery Island (Figs 17,.18 &19) was vegetated
by a closed rush assemblage dominated by Juncus kraussii with patchy tall open shrubs of Melaleuca
cuticularis (Saltwater Paperbark) to about 4m in height. Casuarina obesa (Saltwater Sheoak) in poor
condition (of similar height and sparse cover to the Paperbark) was also present along some parts of this
southern slope. Also common were Ficinia nodosa and Bolboschoenus caldwellii (the latter dormant at the
time of survey). Sarcocornia quinqueflora, Suaeda australis and *Sporobolus africanus were present
along a narrow tidal flat that extended along part of the estuarine southern edge of the dune.
The vegetation of the sand dune crest was predominantly a grass and sedgeland to about 0.5m in height
dominated by Ficinia nodosa and naturalized alien taxa including *Avena barbata (Wild Oats), *Briza
maxima, *Bromus diandrus (Greater Brome),* Hainardia cylindrica, *Lolium perenne (Perennial Rye
Grass), *Lolium rigidum, *Romulea sp. (Guildford Grass) and *Ursinia anthemoides. Jacksonia furcellata
shrubs to about 3m in height were also present on the dune.
There was a more species-rich assemblage of indigenous plants on the northern slope of the dune. Here,
Casuarina obesa (Saltwater Sheoak) (in poor condition) formed open woodland of less than 6m in height.
The shrub layer was mainly Halosarcia indica subsp. bidens and Frankenia pauciflora with the annual
herbs Angianthus preissianus, Cotula cotuloides, Daucus glochidiatus (Native Carrot) and Triglochin
mucronata (Prickly Arrowgrass). Also common were *Atriplex hastata, Bolboschoenus caldwellii (dead or
dormant), Calandrinia calyptrata, Chenopodium glaucum,* Hainardia cylindrica, Halosarcia
halocnemoides subsp. halocnemoides, Halosarcia syncarpa, Lawrencia spicata, *Polypogon maritimus,
*Sporobolus africanus and Suaeda australis.
The vegetation of the supratidal flats and fringes of the tidal lagoons on the northern flank of the island
was a low heath of Halosarcia halocnemoides subsp. halocnemoides and Halosarcia syncarpa over the
annual herb Triglochin mucronata. .
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2. Florida Beach
The highly modified narrow coastal reserve fronting the residential development of Florida Beach (Figs 20
& 21) was vegetated by a sparse assemblage of naturalized alien species with very few indigenous species
remaining. The vegetation and the foredune just north of the housing area were first inspected by the
SWALE group in the spring of 2003 and were earmarked for inclusion in a SWALE transect. However
much of this was modified shortly afterwards when the golf course was installed and the disturbed dunes
subsequently brushed with cut branches and planted with *Ammophila arenaria (Marram Grass). The
SWALE transect was established in the summer of 2005 in the low dunes directly in front of the housing
area.
The rhizomatous colonizing grass Spinifex hirsutus was abundant on the low incipient foredune of Florida
Beach with the sparse herbs *Cakile maritima and *Euphorbia paralias. Olearia axillaris (Coastal Daisy
Bush) formed a heath to about 1m in height on the foredune crest amongst sparse annual and perennial
herbs including *Ammophila arenaria, *Crassula glomerata, Ficinia nodosa, *Oenothera drummondii
(Coastal Evening Primrose) *Pelargonium capitatum (Rose Pelargonium) and *Trachyandra divaricata.
The leeside of the foredune was sparsely colonized with *Oenothera drummondii less than about 20cm in
height. The adjoining swale retained some remnant vegetation with Olearia axillaris and semi-prostrate
Acacia saligna (Orange Wattle) to about 1m in height forming a cover of 25-75% with Acanthocarpus
preissii, *Pelargonium capitatum and Scaevola crassifolia.
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3. Seal Rock, Yalgorup National Park
The coastal zone between Tim’s Thicket and White Hill encompassed a large area of near-to-pristine
closed scrub and an uncommon scrub to low forest of Eucalyptus decipiens and Eucalyptus
gomphocephala. Present in parts of this area (particularly around Tim’s Thicket) there were many informal
vehicle tracks, quarries, small illegal rubbish dumps and areas of mobile sands disturbed by vehicle usage.
The four-wheel-drive access point to the beach at Seal Rock was chosen as a site to record an example of
the coastal vegetation of Yalgorup National Park.
The incipient foredune adjacent to Seal Rock (Figs 22, 23, 24 and 25) was colonized by *Cakile maritima,
Spinifex longifolius and *Tetragonia decumbens. On the seaward slope of the foredune, this assemblage
graded into a heath less than 50cm in height that was dominated by Leucophyta brownii and also included
Carpobrotus virescens, Ficinia nodosa, Olearia axillaris, *Pelargonium capitatum (Rose Pelargonium)
and Scaevola crassifolia (Thick- leafed Fanflower) The upper slope and crest of the foredune supported
an open heath of Alyxia buxifolia, Diplolaena dampieri, Olearia axillaris (Coastal Daisy Bush) and
Spyridium globulosum (Basket Bush) to about 1 m in height. ( (This was similar to the assemblage that
reached about 1.5m in height on the leeside slope of the dune) Common associates of this vegetation were
Acacia rostellifera, Acanthocarpus preissii, *Bromus diandrus, Conostylis candicans subsp. calcicola,
Daucus glochidiatus, Hardenbergia comptoniana (Native Wisteria), Hibbertia cuneiformis (Cut leaf
Hibbertia), *Lagurus ovatus (Hare’s Tail Grass), Lepidosperma gladiatum, Leucopogon parviflorus,
Myoporum insulare (Boobialla), Ozothamnus cordatus, Senecio pinnatifolius, *Sonchus oleraceus,
Sporobolus virginicus and *Trachyandra divaricata.
There was a wide degraded area on the lower slope on the leeside of the foredune that was formerly used
as a vehicle track leading to the nearby blowout. This area was a species-depauperate weedy herbland
dominated by *Trachyandra divaricata,*Dischisma arenarium and *Lagurus ovatus with occasional
shrubs of Acacia rostellifera (Summer-scented Wattle) and occasional remnants of Brachyscome
iberidifolia, Carex preissi, Dryandra lindleyana subsp. lindleyana (Couch Honeypots) and Trachymene
caerulea (Rottnest Island Daisy).
The vegetation east of the old track was a large closed scrub of Melaleuca huegelii (Chenille Honeymyrtle)
to about 4m in height with the climber Clematis linearifolia (Old Man’s Beard) over sparse shrubs of
Alyxia buxifolia, Rhagodia baccata and Threlkeldia diffusa. This vegetation was in excellent condition and
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the understorey was a species-rich annual herb and geophyte sward that included few naturalized alien
taxa, in contrast to the nearby weedy track. A high rate of seedling recruitment was recorded throughout
the understorey of this scrub. Common in the understorey were Apium annuum, Caladenia latifolia (Pink
Fairies), Calandrinia brevipedata, Carex preissii, Crassula sp., Daucus glochidiatus (Native Carrot),
Geranium retrorsum, Hydrocotyle tetragonocarpa, Lobelia tenuior, Parietaria debilis (Native Pellitory)
and Ranunculus sessiliflorus.
In the dampland at the eastern end of the Melaleuca huegelii scrub, there was a patchy disturbed zone of
sparse tall shrubs of Melaleuca viminea to about 3m (with younger shrubs common at about 40 cm in
height). Juncus kraussii (Sea Rush), the sedges Baumea juncea, Ficinia nodosa and Gahnia trifida and an
herb layer mainly dominated by the naturalized alien *Dittrichia graveolens were also present. The herbs
included Apium annuum,* Brassica tournefortii, *Cerastium glomeratum, *Crassula glomerata, *Fumaria
muralis, Hydrocotyle tetragonocarpa, Podolepis lessonii, *Polypogon tenellus and *Rumex crispus. The
remainder of the dampland was a Melaleuca viminea low closed forest to about 8m in height over sparse
sedges. The latter (practically impenetrable) formation extended to a low forest of Eucalyptus
gomphocephala (Tuart) on the low limestone plateau east of the dampland. The Tuart had a closed scrub
understorey of Dryandra sessilis (Parrot Bush) and Spyridium globulosum with occasional mallees of
Eucalyptus decipiens also present.