Overview

Distribution

Range Description

Posidonia sinuosa is endemic to western and southern Australia. It is distributed from Kalbarri to Eyre in Western Australia and from the head of the Great Australian Bight to Encounter Bay, South Australia.
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Physical Description

Type Information

Type locality: Point Atwick, Garden Island, Western Australia
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Ecology

Habitat

Habitat and Ecology

Habitat and Ecology
Posidonia sinuosa is widely distributed in marine embayments and near shore areas on the western and southern coasts of Australia from low water to 15 m depth in sandy substrates. It may form meadows with Amphibolis spp. and typically grows in linear rows up to 50 cm wide, parallel to prevailing direction of water movement (Cambridge and Kuo 1979). This species is slow growing and has a long recruitment time of 20 years.

Posidonia sinuosa has inflorescences born on flattened, leafless peduncles, with reduced, hermaphroditic flowers and filiform pollen. Inflorescence of P. sinuosa are well hidden below the "umbrella-like" meadow canopy at ~10 cm above the sediment. Anthesis and fruiting occurs from August to January (Womersley 1984).

Posidonia sinuosa meadows have a high number of tightly packed shoots with overhanging semi-permanently bent top portions. This species has high leaf density surrounding the flowers which may prevent the pollen from escaping out of the meadow into the overlying water column. This likely leads to greater neighbour to neighbour pollination in this species (Smith and Walker 2002).

Systems
  • Marine
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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
VU
Vulnerable

Red List Criteria
A2ce

Version
3.1

Year Assessed
2010

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.

Contributor/s

Justification
Posidonia sinuosa is endemic to western and southern Australia. This species is slow growing and has a long recruitment time of 20 years. There have been major areas of loss across the range of P. sinuosa which have caused significant population declines. Major threats to this species are a decrease in water quality, sedimentation and coastal development. This species is more susceptible to detrimental human activities due to slower growth and less flowering than other Posidonia spp. Over the last 60 years (three generation lengths), the recorded declines in areas of this species suggests a population reduction greater than 30%. Therefore this species is listed as Vulnerable under criterion A2.
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Population

Population
There have been major areas of loss across the range of Posidonia sinuosa due to human activities, which have caused significant population declines. Based on 11 studies during the period between 1990 and 2000, there was a 1.2 % annual decline in the area of this seagrass (Orth and Dennison 2007). Over the last 60 years (three generation lengths), the recorded declines in areas of this species suggests a population reduction greater than 30%.

In one area of P. sinuosa's distribution, 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 lead to contaminated effluents and increased nutrient loads. Between 1954 and 1978 the meadow in this region 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 (Cambridge et al. 2002).

Population Trend
Decreasing
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Threats

Major Threats
Major threats to this species are excessive nutrient inputs, eutrophication, sedimentation and pollution, and dredging and sand mining activities. Coastal developments such as port development are also threatening for this species.
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Management

Conservation Actions

Conservation Actions
Posidonia sinussa is protected in various Marine Protected Areas (MPAs), in Fisheries Acts, National and Marine Park Acts. There are no specific conservation measures for this species.
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