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Seagrasses
Many areas of the shallow sea bottom are covered with a lush growth of aquatic “grasses,” collectively called seagrasses. Seagrasses are flowering plants adapted to live submerged in seawater, but are not true grasses.
Of the 58 species of seagrass living worldwide a staggering 31 species live in Australia, making Australia a major seagrass centre, two of these species Zostera capricorni and Posidonia australis are found in the Pittwater Waterway (the latter species southern limit is Pittwater).
Seagrass beds are found in relatively sheltered areas, are usually rich in species diversity and are therefore high in productivity.
The relationship between seagrass beds and economically viable fish habitat is well documented however a large range of biota may also be found within these habitats including snails, amphipods, various crustaceans, echinoderms and isopods and a variety of algae and other epiphytic flora.
Seagrasses are under threat, their specialised ecosystems require intensive management, activities such as trampling by people and dogs (particularly at low tide) resulting in a loss of light through sediment input can be detrimental to seagrasses.
Sediment and nutrient input from fertilisers, lawn clippings, poorly managed development (particularly on-site waste water systems and boat jettys/moarings) and the propellers (and effluent) from boats also regularly lead to serious problems for seagrasses in the Pittwater Waterway. On a broader scale, trawling and dredging is also causing irreversible effects on seagrass beds.
Pittwater Council has incorporated Seagrass Conservation into its Development Control Plan so as to assist and guide developers and the community into the right direction when related matters arise.
Where in Pittwater are they found?
- Careel Bay
- Narrabeen Lagoon
- Barrenjoey Spit
- the Western Foreshores of Pittwater (e.g Towlers Bay).
What plants dominate them?
- Zostera capricorni
- Posidonia australis