Posidonia australis 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Plantae Tracheophyta Liliopsida Alismatales Posidoniaceae

Scientific Name: Posidonia australis Hook.f.
Common Name(s):
English Species code: Pa
Taxonomic Notes: This species is a member of the P. australis complex (P. australis Hook.f., P. sinuosa Cambridge & J.Kuo, P. angustifolia Cambridge & J.Kuo) (Campey et al. 2000).

Assessment Information [top]

Red List Category & Criteria: Near Threatened ver 3.1
Year Published: 2010
Date Assessed: 2007-10-23
Needs updating
Assessor(s): Short, F.T., Carruthers, T.J.R., Waycott, M., Kendrick, G.A., Fourqurean, J.W., Callabine, A., Kenworthy, W.J. & Dennison, W.C.
Reviewer(s): Livingstone, S., Harwell, H. & Carpenter, K.E.
Posidonia australis is endemic to southern Australia and northeast Tasmania. The overall population has experienced serious declines documented in 18 studies with an annual decline of 1.8%. It is a slow growing species and takes a long time to recolonize when removed. Major threats to Posidonia australis are coastal development, eutrophication and pollution and sedimentation. Over three generation lengths (15 years) the overall decline is estimated to be 27% which is close to the threshold for the Vulnerable category under A2 criterion with direct observations, a decline in habitat quality, actual and potential levels of exploitation and the effects of pollutants. Therefore this species is listed as Near Threatened.

Geographic Range [top]

Range Description:Posidonia australis is endemic to the southern half of Australia, including north and east Tasmania. It is found sporadically from north of Shark Bay in Western Australia southward and along the coast to Walis Lake in New South Wales.
Countries occurrence:
FAO Marine Fishing Areas:
Indian Ocean – eastern; Pacific – southwest
Additional data:
Lower depth limit (metres):22
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:Posidonia australis has experienced serious declines documented in 18 studies with an annual decline of 1.8% (Orth and Dennison 2007). Some areas are in recovery. It is common in seagrass communities in New South Wales, Victoria, and Tasmania (Green and Short 2003).

The Posidonia community in Jervis Bay, Australia has suffered large declines in the past (Meehan and West 2000). This community has taken over 25 years to recolonize a total area in this bay of 0.4 ha and is likely to take over a century to repair completely, assuming there is no further damage. This recolonization appears to be entirely by vegetative re-growth. This location has excellent water quality and conditions ideal for recovery (Meehan and West 2000).

Cockburn Sound has been subjected to steady degradation since 1954, with the establishment of an oil refinery and the successive establishments of steel works, fertilizer factories, sewage-treatment facilities, and a power station. This has led to contaminated effluents and increased nutrient loads. Between 1954 and 1978 the meadow in this region (containing P. australis) was reduced from 4,200 to 900 ha. (Cambridge and McComb 1984).

Seagrass loss (Posidonia australis and P. sinuosa) in Oyster Harbour between 1962 and 1988 was the culmination of diffuse nutrient and sediment influx from rural catchments but recovery is possible with time. At the rates of growth measured, transplants placed one m apart will grow together to form a meadow in less than five years (Cambridge et al. 2002).
Current Population Trend:Decreasing
Additional data:
Population severely fragmented:No

Habitat and Ecology [top]

Habitat and Ecology:The temperate seagrass species Posidonia australis can form large monospecific meadows through strong rhizomatous growth, and these meadows are found throughout southern Australia. Posidonia austrails ecosystems are known to be highly productive and are apparently slow growing (West 1990). It grows in continuous meadows in 1-15 m water in sheltered bays (Cambridge and Kuo 1979).

Posidonia australis exists in well developed meadows and typically has continuous cover (Cambridge and Kuo 1979). This species is common in the subtidal environments in Western Australia, to depths of about 12 m. It can exist in depths of up to 22 m in clear non-polluted water. It often grows in meadows mixed with Zostera tasmanica and Halophila ovalis in less-protected areas dominated by sandy sediments in southeast region of Australia, and occupies the gaps between meadows and areas close to water inputs. It is a slow growing species.

Posidonia australis is the dominant seagrass species in a number of southeastern Australian estuaries. This species is important for primary productivity in these systems, supports a variety of detritus feeders and macrofauna, and is an important nursery area for fish (Meehan and West 2004).

Few seedlings of this species are seen in the field. Seedlings likely do not play a role in recovery of damaged meadows as they do not form rhizomes quickly and therefore spread slowly (Meehan and West 2004). The recruitment rate (and generation length) is estimated at five years.

Posidonia australis meadows have a low number of loosely packed shoots with upright-standing leaf blades, and thinning-out of upright-standing leaf blades in the top half of the canopy creating an "open" canopy. Posidonia australis meadows are typically much smaller than those of P. sinuosa. Flowers of this species occur in the top of the canopy, within a zone of minimal leaf area. This may lead to fewer obstructions in the pollen dispersal path (Smith and Walker 2002).
Continuing decline in area, extent and/or quality of habitat:Yes
Generation Length (years):5

Use and Trade [top]

Use and Trade: In southern Australia, leaves were harvested from the beach for soil conditioner and compost mixes (Green and Short 2003).

Threats [top]

Major Threat(s): Major threats to Posidonia australis are human-induced activities causing increased epiphytism, blocking light and increased drift algal loads (Green and Short 2003). Coastal activities such as port and industrial development also cause direct physical damage. Mining and dredging, eutrophication and pollution from industry, aquaculture and farming, as well as direct physical damage by recreational and commercial boating activities, and to some extent trawling activities also threaten this species (Green and Short 2003).

Posidonia australis is a slow growing species and does not form rhizomes quickly and therefore spreads slowly.

Conservation Actions [top]

Conservation Actions: An application has been submitted for Posidonia australis to be added to the threatened species list for New South Wales and is currently (May 2009) out for public comment. It is expected to be accepted. This will afford the species a level of legal protection in the Australian State (G. Kendrick pers. comm. 2009).

Posidonia australis is included in Shark Bay World Heritage Property which contains more than 4000 kmĀ² of seagrass beds of high density. Seagrass beds cannot be damaged without a permit in the state of New South Wales in Australia. It is also protected in various Marine Protected Areas (MPAs), in Fisheries Acts or in National or Marine Park Acts (Green and Short 2003).

More research is needed regarding conservation planning and population trends should be monitored.  Conservation measures needed include site protection and management, increased educational awareness, and legislation and enforcement at the national and local levels.

Citation: Short, F.T., Carruthers, T.J.R., Waycott, M., Kendrick, G.A., Fourqurean, J.W., Callabine, A., Kenworthy, W.J. & Dennison, W.C. 2010. Posidonia australis. The IUCN Red List of Threatened Species 2010: e.T173333A6993340. . Downloaded on 24 September 2018.
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