Seagrasses are sensitive ecosystems that are impacted by changes to water quality. High levels of nutrients entering these ecosystems causes rapid growth of epiphytes (plants that attach to other plants) that smother the blades of seagrass. This blocks the ability of seagrass to photosynthesise. Sediment run off into coastal waters can also reduce light penetration, smother seabed habitat and introduce nutrients and toxins.
Nutrient loads from terrestrial sources, particularly nitrogen and phosphorous have been identified as key threats to the future sustainability of the seagrass communities of Geographe Bay, Cockburn Sound and the Swan Canning estuary. Recent modelling of the catchments has identified current nutrient loads to be well above desired levels for a number of the drains and estuaries that enter the bay, including the Vasse Diversion Drain and the Vasse Wonnerup Estuary. With population growth, increased development and urbanisation forecast in these catchments in the near future, nutrient loads are predicted to rise even higher and place more pressure on the seagrass communities.
Further, changes in seasonal flow regimes from winter to summer flow as a result of treated sewage water discharge or changing rainfall patterns associated with climate change may also impact on the seagrass communities.
This has consequences for the Blue Swimmer Crab who calls the seagrass meadows home.