Species code: Pn

Posidonia sinuosa is a marine flowering plant, a seagrass belonging to the family Posidoniaceae, native to the temperate coastal waters of southern Australia. It forms extensive meadows on sandy and silty substrates in shallow to moderately deep coastal waters, characterized by long, strap-like leaves arising from a creeping rhizome system that stabilizes sediment. Like other seagrasses, it reproduces both vegetatively through rhizome extension and sexually via flowering and seed production, though growth is slow.

These meadows provide critical habitat and nursery grounds for fish, invertebrates, and other marine life, while also stabilizing seafloor sediments, filtering coastal waters, and contributing to carbon sequestration in marine sediments.

The species is restricted to Australian coastal waters, occupying marine neritic zones alongside adjacent forest and grassland habitats in coastal transition areas. Its range spans the southern coastline, where it forms mixed and monospecific meadows.

Posidonia sinuosa is classified as Vulnerable, with a decreasing population trend. Key threats include coastal mining and quarrying operations that disturb seafloor habitats, broader ecosystem modifications from coastal development and dredging, nutrient and chemical runoff from agricultural and forestry activities, and additional unspecified pollution sources. These pressures degrade water quality, increase turbidity, and physically damage meadow structures, all of which impede the plant's slow recovery capacity.

Conservation measures in Australia include marine protected area designations, water quality monitoring programs, and seagrass restoration trials aimed at re-establishing degraded meadows. Regulatory controls on coastal development and effluent discharge in some jurisdictions also contribute to mitigation efforts.

The species' outlook remains concerning, as ongoing coastal development and diffuse pollution sources continue largely unabated in many areas, and the slow growth rate of Posidonia sinuosa limits its capacity for rapid recovery even where local protections are enforced.