Biodiversity Strategy - Gosford City Council - NSW Government
Biodiversity Strategy - Gosford City Council - NSW Government Biodiversity Strategy - Gosford City Council - NSW Government
Mangroves There are two species of mangrove found in the Gosford area; Avicennia marina (Grey Mangrove) and Argiceras corniculatum (River Mangrove). Mangroves are an important fish habitat (Freewater 2004). Fish feed among the mangroves at high tide and seek refuge within channels of permanent water as water levels fall. Mangroves provide a solid substrate for oysters, barnacles and seaweeds, with more mobile animals such as crabs and molluscs living among the encrusting organisms (Figure 6.2). Decomposing materials from mangroves form the basis of detrital food chains that sustain small invertebrates which are in turn eaten by fish. Fallen timber, aerial roots (which include pneumatophores) and crab burrows all add to the structural complexity of mangrove habitat, providing feeding opportunities and shelter. Within channels of permanent water, exposed roots and submerged snags do likewise. In Gosford, many of the commercially important marine and estuarine species live in mangrove channels as small juveniles; examples include juvenile yellowfin bream, luderick, silverbiddy, sea mullet and flat -tail mullet. Mangrove forests also act as filters by trapping sediments and contaminants and by absorbing nutrients (Freewater 2004). The complex of pneumatophores, roots, trunks and densely packed seedlings within a mangrove forest slows water movement, thereby causing sediment to settle. Mangroves thus help to protect other marine habitats from sedimentation and have been shown to convert excess nutrients into extra growth; this normally being limited by the supply of nitrogen and phosphorus (Freewater 2004). Mangroves also help to stabilise banks and protect them from erosion. The role of mangroves in ameliorating the impact of stormwater runoff must therefore be Biodiversity - Technical Report Page 131
considered. This is true for all riparian and emergent vegetation. Although mangroves are protected under NSW Fisheries legislation, they are now considered to be opportunistic. They have become particularly prolific around creek deltas where mud is accumulating. Their ability to trap and accumulate sediments has resulted has seen their expansion into creeks and other waterways, limiting or denying navigation of marine craft. They are also encroaching into and displacing saltmarsh habitats. This has become an issue of particular concern because saltmarsh habitats have already been considerably reduced in the area as a result of urban expansion. Saltmarshes Saltmarshes play a similar water filtration role to that outlined for mangroves. Biofilms associated with emergent vegetation and root systems are extremely effective in binding contaminants. The high density of saltmarsh plants makes them excellent pollutant filtration systems. Stormwater flows to these systems slow, facilitating the removal of sediments, particulate matter and dissolved contaminants. The habitat is poorly conserved in NSW as continuously more is cleared for development. In Gosford, the frontal levee of the saltmarsh is typically dominated by Sporobolus viginicus, but where drift litter accumulates Suaeda australis, Tetragonia tetragonioides and Sesuvium portulacastrum can also be abundant (Figure 6.3). Casuarina glauca is found higher on the levees. Sarcocornia quinqueflora occurs in the depression landward of the levee, together with Triglochin striata and Samolus repens, in the wetter patches. Dense rush, Jucus kraussii, or sedge, Baumea juncea, comprise the mid-marsh community. Fringing the pools are Phragmites australis, Schoenoplectus litoralis and Schoenoplectus validus, while Ruppia and the alga Lampromthamnion papulosum may be abundant within the pools. Scattered through this zone are isolated Casuarina glauca and mangroves. Figure 6.2 Avicennia marina, seedlings and pneumatophores (Peter Freewater) Biodiversity - Technical Report Page 132
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Mangroves<br />
There are two species of mangrove found in the <strong>Gosford</strong> area; Avicennia marina (Grey<br />
Mangrove) and Argiceras corniculatum (River Mangrove). Mangroves are an important fish<br />
habitat (Freewater 2004). Fish feed among the mangroves at high tide and seek refuge within<br />
channels of permanent water as water levels fall. Mangroves provide a solid substrate for<br />
oysters, barnacles and seaweeds, with more mobile animals such as crabs and molluscs living<br />
among the encrusting organisms (Figure 6.2). Decomposing materials from mangroves form the<br />
basis of detrital food chains that sustain small invertebrates which are in turn eaten by fish.<br />
Fallen timber, aerial roots (which include pneumatophores) and crab burrows all add to the<br />
structural complexity of mangrove habitat, providing feeding opportunities and shelter. Within<br />
channels of permanent water, exposed roots and submerged snags do likewise. In <strong>Gosford</strong>,<br />
many of the commercially important marine and estuarine species live in mangrove channels as<br />
small juveniles; examples include juvenile yellowfin bream, luderick, silverbiddy, sea mullet and<br />
flat -tail mullet.<br />
Mangrove forests also act as filters by trapping sediments and contaminants and by absorbing<br />
nutrients (Freewater 2004). The complex of pneumatophores, roots, trunks and densely packed<br />
seedlings within a mangrove forest slows water movement, thereby causing sediment to settle.<br />
Mangroves thus help to protect other marine habitats from sedimentation and have been shown<br />
to convert excess nutrients into extra growth; this normally being limited by the supply of<br />
nitrogen and phosphorus (Freewater 2004). Mangroves also help to stabilise banks and protect<br />
them from erosion. The role of mangroves in ameliorating the impact of stormwater runoff must<br />
therefore be<br />
<strong>Biodiversity</strong> - Technical Report Page 131