Submerged aquatic vegetation is the term used to describe rooted, aquatic flowering plants which include true seagrasses and freshwater plants. In both estuarine and freshwater systems this vegetation performs a number of important ecological functions that influence the chemistry of the water column and sediments. They also provide a refuge for invertebrates and fish, and food for fish and wading birds, for example the Black Swan.
Submerged aquatic vegetation is increasingly being used as a tool to describe estuary condition. Species composition and distribution of submerged aquatic vegetation in an estuary is dependent on a range of conditions such as water movement, sediment condition, fresh water supply and connectivity to the ocean. This will vary from estuary to estuary, and so submerged aquatic vegetation characteristics equating to good condition will also differ among estuaries.
There are however, common factors that influence the distribution of aquatic plants. These include changes in light, nutrient availability, grazing pressure, flood events and direct physical disturbance by humans. Loss of seagrass habitat is generally equated with ecosystem decline and is most frequently linked to eutrophication (nutrient and organic loading) from the catchment Phytoplankton blooms and excessive growth of epiphytic algae are both symptoms of eutrophication. Both phytoplankton and algae reduce light availability for seagrass growth which in extreme cases can lead to seagrass loss due to shading effects. Cockburn Sound and the Albany Harbours are both examples of the replacement of seagrass by macroalgae as a result of excessive nutrient inputs.
The role of the Department of Water is:
- to develop efficient and repeatable techniques to perform baseline surveys of the extent and distribution of submerged aquatic vegetation in estuaries and
- to identify suitable measures of submerged aquatic vegetation that can be used to describe estuarine condition.