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POSIDONIA AUSTRALIS COMPLEX SEAGRASS MEADOWS DRAFT
DESCRIPTION
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Draft Description
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The ecological community consists of the assemblage of plants, animals and micro-organisms
associated with seagrass meadows dominated by species from the Posidonia australis
complex and occurs mostly in temperate regions of Australia. The ecological community is the
climax community of a successional process that occurs over decades to centuries (Kendrick et
al, 2008).
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The ecological community was nominated as Posidonia australis seagrass beds or Posidonia
dominated seagrass meadows. The Threatened Species Scientific Committee recommended
that the ecological community be assessed as Posidonia seagrass meadows and it was placed
on the 2011 Finalised Priority Assessment List (FPAL) by the Minister for the Environment,
with an assessment period ending in December 2013.
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Further consideration of the definition of this marine ecological community, including an
expert workshop, resulted in a focus on the species of the Posidonia australis complex. The
P. australis complex is one of two distinct groups of Australian Posidonia species; the other
being the P. ostenfeldii complex1. The two groups can be separated on the basis of their leaf
and rhizome characteristics but also their ecological characteristics. The three species of the
P. australis complex (P. australis; P. angustifolia; and P. sinuosa) are the meadow forming
species of the Posidonia genus (Cambridge and Kuo, 1979). It is therefore recommended that
the name of the ecological community be Posidonia australis complex seagrass meadows
(hereafter referred to as ‘the ecological community’).
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The ecological community occurs in temperate/subtropical waters from Shark Bay (25°S) on
the west coast, across southern Australia to Wallis Lake (32°S) on the east coast, around Bass
Strait islands and along the north coast of Tasmania. Latitude 25°S on the west coast and 30°S
on the east coast of Australia is considered to form a boundary between temperate and
tropical seagrass species (Larkum, 1976). Posidonia australis complex seagrass meadows
occurring around islands within the geographic range are also included within the ecological
community.
Name of the ecological community
Location and physical environment
The ecological community typically occurs in subtidal2 waters where salinities are marine (30–
50◦/◦◦), at depths less than 20 m on sand and silty mud substrate (Cambridge and Kuo, 1979;
Carruthers et al., 2007). Posidonia species of the ecological community have been recorded at
depths greater than 20 m. For example, off the west coast, P. angustifolia has been recorded
at a depth of 45 m (Carruthers et al., 2007). However, at depths greater than 20 m, the
meadow structure and function typical of the ecological community is diminished. These
occurrences are therefore excluded from the definition of the ecological community. The
upslope limit of the ecological community is imposed by the requirement for sufficient
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In contrast to Posidonia australis, species of the P. ostenfeldii complex are clump forming and are found in more
exposed, high energy environments (Kuo and Cambridge, 1984).
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Subtidal zones are submerged most of the time, exposed briefly during extreme low tides around full and new
moon events.
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immersion in seawater and tolerable disturbance by water movement (Duarte, 2002). In some
cases, ponding and retention of water at the shallow edge of meadows enables the ecological
community to exist below tide level (Kirkman, pers. comm., 2013). For example, in Corner
Inlet, Victoria, large expanses of the ecological community are exposed at most low tides
(Kirkman, 2009).
The ecological community typically occurs in sheltered habitats, with the nature and degree of
protection from water movement varying across its range. For example,
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
On the south eastern coast of Australia, the high wave energy typical of the coastline
largely restricts the ecological community to estuaries (e.g. Port Hacking, Lake
Macquarie, New South Wales) and open embayments (e.g. Jervis Bay, New South
Wales and Corner Inlet, Victoria). Some small isolated patches occur near protected
rocky platforms and in the lee of offshore islands (e.g. in the lee of Broughton Island,
Bushrangers Bay at Bass Point and in waters at Bittangabee Bay) (West et al., 1989).
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
Along the southern Australian coast, the ecological community occurs in sheltered
habitats affording protection from strong, prevailing south west oceanic swells, such as
gulfs (e.g. Spencer Gulf and Gulf St Vincent, South Australia), embayments (e.g.
Princess Royal Harbour, Western Australia and estuaries (e.g. Oyster Harbour,
Western Australia) (Shepherd and Robertson, 1989). On exposed coastlines, the
ecological community occurs where reefs or islands give local protection from ocean
swell (Carruthers et al., 2007) (e.g. Waterloo Bay, South Australia; Thompsons Bay,
Rottnest Island) or at depths which sufficiently reduce wave energy (e.g. at the base of
exposed cliffs of western Eyre Peninsula) (Shepherd and Robertson, 1989).
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
On the west coast of Australia the ecological community mostly occurs inshore of a
broken line of limestone reefs and barrier islands (Kirkman, 1985; Carruthers, 2007)
which give protection from the full force of oceanic swell. The breaks in the reef
system can be up to many kilometres in length and this is reflected in the occurrence
of the ecological community (Kirkman, 1985). The ecological community reaches its
northern limit on the west coast in the semi-enclosed basin of Shark Bay (Walker,
1989).
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Vegetation
The ecological community occurs as continuous to patchy monospecific and multispecies
seagrass meadows dominated by species from the Posidonia australis complex P. angustifolia, P. australis and P. sinuosa.
The Posidonia australis complex species are slow growing, have persistent rhizomes and are
typically the meadow-forming species of the Posidonia genus (Cambridge and Kuo, 1979).
There is differentiation in the distribution and habitat preferences of the Posidonia australis
complex species that can affect the relative dominance in a meadow of one or other of the
species (refer Table 1). For example, P. australis is the only Posidonia species occurring on the
east coast. Where P. australis and P. sinuosa co-occur, P. australis typically dominates
P. sinuosa in very shallow and more disturbed areas as the shorter and wider leaves of
P. australis are resistant to mechanical damage caused by water movement . Conversely,
P. sinuosa typically dominates P. australis in slightly deeper and more sheltered water
(Kirkman and Walker, 1989; Shepherd and Robertson, 1989). In deeper water and in deeper
sand, P. angustifolia is often the dominant species of Posidonia (Shepherd and Roberston,
1989).
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Table 1 Distribution, habitat preference and meadow structure of Posidonia australis complex
species.
Sources: Cambridge and Kuo, 1979; Edgar, 2012.
Posidonia
species
Distribution
Environment
Depth (m)
Meadow
structure
P. australis
Shark Bay, WA
around the southern
and southeastern
coastlines to Wallis
Lake, NSW and along
the northern coast of
Tasmania and Bass
Strait Islands
Sheltered sand and
mud environments
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Dense
monospecific
meadows,
although
frequently
found with
other Posidonia
species
P. angustifolia
Houtman Abrolhos,
WA to Encounter Bay,
South Australia and
along northern coast
of Tasmania
Moderately exposed
sand environments
2-35
Dense
monospecific or
mixed species
meadows
P. sinuosa
Shark Bay, WA to
Kingston, SA
Moderately exposed
and sheltered sands
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Dense
monospecific
meadows;
usually found
with P. australis
in sheltered
embayments or
with
Amphibolis
species in less
enclosed
waters
Both continuous and patchy meadows of the ecological community often contain mosaics of
bare sand or other seagrass species that occupy edges, blowouts3 and small areas of meadows
(Kirkman and Kuo, 1990). In some cases, sparse meadows of the ecological community may
have an understorey of smaller seagrass species. Seagrass species that may be found growing
with the ecological community include: Amphibolis antarctica, A. griffithii, Cymodocea
angustata, Halophila uninervis, H. ovalis, Heterozostera tasmanica and Syringodium
isoetifolium.
Also associated with the ecological community is a diverse assemblage of benthic flora, in the
form of micro and macro epiphytes and non-epiphytic algae and a complex layer of
periphyton4 on the seagrass leaves (Klumpp, et al., 1989; Carruthers, 2007).
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Blowout – an area in a seagrass meadow denuded of seagrass through natural or anthropogenic disturbance.
Blowouts are typically areas of instability in sediment movement, shape and size and seagrass species
composition (Kirkman, 1985).
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Periphyton comprising of diatoms, macroalgae, encrusting algae, bacteria, fungi and sedimented debris
(Klumpp, et al., 1989)
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Fauna
The ecological community is highly productive and provides habitat, shelter and food for a
diverse array of fauna permanently and temporarily inhabiting the ecological community.
Posidonia australis complex seagrasses are not usually a direct food source for grazers.
However, a few fish, notably monacanthids (Wressnig and Booth, 2008) graze the leaves.
Mostly, the seagrass provides a stable substratum for the establishment of other plants and
animals as epiphytes and epifauna, which in turn support higher food chains (Walker et al.,
1991). The ecological community also provides important nursery habitat5 for some fish and
crustaceans. For example, in southeastern Australia, the commercially important
Acanthopagrus australis (yellowfin bream), A. butcherii (black bream), Mugil cephalus (sea
mullet), Girella tricuspidata (luderick) (Burchmore et al., 1984; McNeill et al., 1992;
Rotherham and West, 2002; West and Jones, 2001) and in Western Australia, Panulirus cygnus
(Western Rock Lobster) (WA Department of Fisheries, 2011) spend part of their juvenile life in
the ecological community.
While rich in fauna, the ecological community does not have characteristic fauna (Hutchings,
1982; Howard et al., 2006). Seagrass fauna tend to respond to physical environmental
parameters such as hydrological and sediment characteristics of a particular meadow
(Hutchings, 1982), rather than associate with particular seagrass meadows (Howard, et al.,
2006). Some common fauna associated with the ecological community are identified in
Table 2.
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Nursery habitats are defined as those that contribute disproportionately to the size and number of adults
relative to other juvenile habitats (Cullen–Unsworth and Unsworth, 2013).
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Table 2 Some common fauna associated with Posidonia australis complex seagrass meadows
(Note: families and species are not directly related across the table columns)
Sources: Walker et al., 1991; Bell et al., 1992; Kinloch et al. 2007
Taxa
Examples of Common
Families
Examples of Common Species
Ambassidae
Apogonidae
Atherinidae
Gobiidae
Monacanthidae
Mugilidae
Scorpaenidae
Syngnathidae
Theraponidae
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Siphamia cephalotes
Kestatherina brevirostris
Nesogobius pulchellus
Acanthaluteres spilomelanurus
Scobinichthys granulates
Upeneichthys porosus
Gymnapistes marmoratus
Stigmatopora argus
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Alpheus edwardsii
Philocheras intermedius
Litocheira bispinosa
Latreutes compressus
Naxia aurita
Macrobrachium sp.
Chlorotecella spinicaudus
Nectocarcinus integrifrons
Processa gracilis
Rhynchocinetes sp.
Fish
Crustaceans
Decapods Alpheidae
Crangonidae
Goneplacidae
Hippolytidae
Majidae
Palaemonidae
Pandalidae
Portunidae
Proccessidae
Rhynchocinetidae
 Crabyzos longicaudatus
 Cerceis acuticaudata
 Notomysis australiensis
Isopods Idoteidae
Sphaeromatidae
Mysidacea
Polychaetes
Molluscs
Trochidae
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Echinoidea
Ophiuroidea
Asteroidea
Holothuroidea
 Ophiaconis opacum
 Uniophora granifera
Cantharidus bellulus
Clanculus dunkeri
Diala lauta
Mitrella lincolnensis
Thalotia conica
Idiosepius notoides
Echinoderms
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Key diagnostic characteristics and good condition categories
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The key diagnostic characteristics6 presented here summarise the main features of the
ecological community. These are intended to aid the identification of the ecological
community, noting that a broader description is given in the other sections.
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National listing focuses legal protection on remaining patches of the ecological community
that are most functional, relatively natural (as described by the ‘Description’) and in relatively
good condition. Key diagnostic characteristics and condition classes assist in identifying a
patch of the threatened ecological community; determine when the EPBC Act is likely to apply
to the ecological community; and to distinguish between patches of different quality. They
provide guidance for when a patch of a threatened ecological community retains sufficient
conservation values to be considered as a Matter of National Environmental Significance, as
defined under the EPBC Act. Patches of the ecological community that do not meet the
minimum good condition classes are excluded from full national protection. This means that
the referral, assessment and compliance provisions of the EPBC Act are focussed on the most
valuable elements of the ecological community.
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The ecological community may exhibit various degrees of disturbance and degradation.
Natural variation and degree of degradation has been taken into account in developing the
key diagnostic characteristics and condition classes.
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While very degraded/modified patches are not protected as the ecological community listed
under the EPBC Act, it is recognised that patches that do not meet the condition thresholds
may still retain important natural values and may be critical to protecting those patches that
meet minimum thresholds. They may also be protected through State and local laws or
schemes. Therefore, these patches should not be excluded from recovery and other
management actions. Suitable recovery and management actions may improve these patches
to the point that they may be regarded as part of the ecological community that is fully
protected under the EPBC Act. Management actions should, where feasible, also aim to
restore patches to meet the high quality condition thresholds outlined below.
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For EPBC Act referral, assessment and compliance purposes, the national ecological
community is limited to patches that meet the following key diagnostic characteristics and
condition thresholds:
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Key diagnostic characteristics
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The ecological community is the suite of organisms including and associated with Posidonia
australis complex dominated seagrass meadows. Key diagnostic characteristics for describing
the ecological community are:
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 Occurs in temperate/subtropical waters from Shark Bay in Western Australia (25 ◦S) to
Wallis Lake in New South Wales (32◦S) and around Bass Strait and other islands and along
the north coast of Tasmania.
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 Consists of continuous to patchy seagrass meadows with at least 50% Posidonia australis
complex seagrass cover of total seagrass cover.
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 Occurs in shallow subtidal coastal waters (<20 m) in locations with protection from high
wave energy. For example, exposed waters with high water movement but protected by
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Key diagnostic characteristics are the main features of the ecological community. Key diagnostic characteristics
do not describe the ecological community in detail but rather they are intended to aid the identification of the
ecological community in situ.
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reefs, in the lee of islands or at a depth of reduced wave energy; in sheltered gulfs and
semi-enclosed embayments; and downstream in estuaries.
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 Occurs on sand or silty-mud substrate.
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Exclusions
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The following are excluded from the ecological community:
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 Occurrences of the ecological community at depths greater than 20m.
Good condition categories
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Meadow Size
Posidonia australis
complex species
cover of total
meadow area7
Minimum shoot
density of
Posidonia australis
complex species
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Small (<1 ha)
Moderate (1-10ha)
Large (>10ha)
>50%
>30%
>30%
and
and
and
100 shoots/m2
25 shoots/m2
10 shoots/m2
Patch definition
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A patch of the ecological community is defined as a continuous or patchy seagrass meadow. A
patch may include bare area or substrate (e.g. sand) or small scale disturbances such as boat
scours or blowouts that do not alter its overall functionality (functionality here refers to
ecological processes such as the movement of fauna, dispersal of plant propagules, provision
of food and habitat attributes such as refuge or nursery function, all of which can operate at
small to large scales).
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Buffer zones enhance protection of a patch by avoiding or minimising potential disturbance
from surrounding land and sea uses or activities. While the buffer zone is not formally part of
the ecological community, it should be taken into account when considering likely significant
impacts during EPBC Act decision-making.
Buffer Zones
It is recommended that an appropriately sized buffer zone be applied from the outer edge of a
patch. The size of the buffer zone should increase with increasing intensity and likely impact
of threat. The impact of a threat on the ecological community will vary with the activity type.
Impacts of some activities are localised, for example, the damage caused by boat propellers
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Meadow area includes areas of bare substrate including blowouts.
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and moorings. In circumstances of localised impacts, a buffer zone of 50 metres is
encouraged. Impacts from other activities can occur kilometres away in the case of plume
generation from dredging or changed hydrology due to sea wall construction. In such
circumstances an appropriate buffer zone will be in the order of several kilometres. With
regards to dredging activities, the application of buffer zones should be in line with national
and state guidelines on dredging activities.
Timing of Surveys
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Identifying the ecological community and its condition is possible at most times of the year,
however, consideration must be given to the role that season and disturbance history may
play in an assessment. For example, the ecological community exhibits seasonality of growth,
with maximum growth occurring during the spring and summer. In the autumn and winter,
much of this growth dies and is broken off. Severe storms or flooding may also cause loss of
seagrass leaves, leaving only the rhizome layer or a few leaves.
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Timing of surveys should provide for a reasonable interval after a disturbance (natural or
human-induced) to allow for regeneration of Posidonia species to become evident, and be
identified.
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In the context of actions that may have ‘significant impacts’ and require approval under the
EPBC Act, it is important to consider the surrounding environment and seascape context of
patches that meet the condition thresholds. The following indicators should be considered
when assessing the impacts of actions or proposed actions under the EPBC Act, or when
considering recovery, management and funding priorities for a particular patch:
 Large meadow and/or large area to boundary ratio – larger area/boundary ratios are less
exposed and more resilient to edge effect disturbances.
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Good faunal habitat as typically indicated by medium to dense seagrass cover, refuge,
nursery habitat and contribution to movement corridors.
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Presence of listed threatened or migratory species.
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Connectivity to other patches or marine habitats. In particular, a patch in an important
position between (or linking) other patches/habitats in the seascape including patches of
the ecological community that are outside the minimum patch size (taking into account
that connectivity should aim to not exacerbate the incidence or spread of threats e.g.
invasive species).
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Minimal invasive species or where these can be managed easily.
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Patches that meet condition thresholds in areas where the ecological community has been
otherwise heavily degraded.
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At the edge of the range of the ecological community.
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Unique variants of the ecological community.
Surrounding environment and seascape context
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Area critical to the survival of the ecological community
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Areas that meet the key diagnostic characteristics and condition classes are considered critical
to the survival of the ecological community. Adequate light for photosynthesis is of critical
importance to the survival of the ecological community. Therefore, also critical to the survival
of the ecological community is the water column above the ecological community being of a
quality adequate for photosynthesis.
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Additional areas such as adjoining habitats and a minimum 50 metre buffer zone, and areas
that meet the description of the ecological community but not the condition thresholds are
also considered important to the survival of the ecological community.
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BIBLIOGRAPHY
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Cambridge ML and Kuo J (1979). Two new species of seagrasses from Australia, Posidonia
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WA Department of Fisheries (2011). Fisheries Fact Sheet: Seagrasses.
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