Seagrasses

Seagrass meadows are important to near-shore coastal ecosystems, where they play significant roles in important geomorphological and ecological processes (Walker et al., 1989). Meadows represent significant nursery habitats for a wide range of marine fauna, they are also highly productive and provide a substrate for algae, small animals and microbes which are significant food sources for other organisms (Hastings et al., 1995). The canopy of seagrass beds is capable of reducing current velocities, thus reducing erosion, enhancing sediment stability, promoting sedimentation and maintaining water clarity (Hastings et al., 1995; Lee Long et al., 2000).

There are three seagrass species found in the vicinity of the proposed development at Maud's Landing. These Posidonia coriacea, Halophila ovalis and Amphibolis antarctica. Both Posidonia coriacea and Amphibolis antarctica are temperate species, and the communities found at the Maud's Landing site represent the northern-most extent of their distribution, and therefore should be considered regionally important. Halophila ovalis is an important food source for the local dugong populations. It has been found that loss of this food source can lead to major declines in the dugong population (Preen and Marsh, 1995)

Threats

The construction associated with the Maud's Landing development will directly affect about 5 ha of sandy substrates and dependant communities (i.e. seagrass meadows). It is also likely to reduce water quality due to increase in water column sediments, therefore decreasing the rate of light penetration though the water column, which causes deterioration and loss of seagrass.

Increases in human activities in the Maud's Landing area as a result of this development may increase the nutrient levels of the waters, through;
· sewage discharge
· contaminated groundwater inputs, and
· surface run-off.
This increase in nutrient levels can stimulate phytoplankton blooms and promote excessive growth of epiphytic algae, both occurrences have deleterious effects on seagrass survival.

Loss of seagrass causes a significant reduction in habitat, and therefore potentially important loss of species diversity and reduction in ecosystem functioning (Hastings et al., 1995). Loss of seagrasses may also result in net erosion nearshore and, potentially, along beach areas (Hastings et al., 1995). If seagrass plants (including their rhizomes) have been removed from an area, seagrass beds tend not to regrow or recolonise that area (Kirkman, 1985).

References

Hastings, K., Hesp, P. and Kendrick, G. A. (1995) Seagrass loss associated with boat moorings at Rottnest Island, Western Australia. Ocean and Coastal Management, 26(3): 225-246.
Kirkman, H. (1985) Community structure in seagrasses in southern Western Australia. Aquat Bot 21: 363-375.
Lee Long, W. J., Coles, R. G. and McKenzie, L. J. (2000) Issues for seagrass conservation management in Queensland. Pacific Conservation Biology 5(4): 321-328.
Preen, A. and Marsh, H. (1995) Response of dugongs to large-scale loss of seagrass from Hervey Bay, Queensland, Australia. Wildlife Research 22: 507-519.
Walker, D. I., Lukatelich, R. J., Bastyan, G. and McComb, A. J. (1989) Effect of boat moorings on seagrass beds near Perth, Western Australia. Aquatic Botany, 36: 69-77.