Macroinvertebrates (waterbugs) are important or ecological processes and also indicate the health of waterways.
The strategy will consider opportunities to protect and enhance macroinvertebrate communities through on-ground works and other initiatives e.g.
- Planting vegetation along streams
- Providing natural stream flows
- Reducing the impact of stormwater
There are thousands of macroinvertebrate species in rivers, wetlands and estuaries across the region, including many types of aquatic insects, worms, snails, mites and crustacea. With some tolerant of waterway degradation and others sensitive to degradation (for example, changes in flow, water quality and habitat), macroinvertebrates are good indicators of waterway health.
Streamside vegetation management, maintenance of natural streamflows and effective management of urban and rural stormwater, and point sources of pollutants all contribute to improving environmental conditions to support macroinvertebrate communities.
The current status of macroinvertebrates in each catchment is based on the land use macroinvertebrate response (LUMaR) index and habitat suitability modelling.
The overall score for macroinvertebrates is very low. Much of the catchment has been impacted by increasing expansion of urban and industrial areas that result in changes to stream flows, water quality and instream habitat (e.g. concrete channels and pipes, and erosion that occurs during wet weather flows).
Maribyrnong and Werribee
The overall score for macroinvertebrates is moderate. Values are highest in forested headwaters with degradation increasing towards the lower reaches, which are increasingly impacted by urban runoff.
The overall score for macroinvertebrates is moderate. It is higher in forested headwaters of the Bunyip and Tarago Rivers, eastern rural catchments, Phillip and French Islands, and south-eastern Mornington Peninsula, and lower for those streams exposed to urban runoff and which have limited streamside vegetation and instream habitat.
The overall score for macroinvertebrates is high and very high along the Yarra main stem, in the upper catchment and across most of the middle catchment (including Diamond, Olinda and Stringybark creeks). In the lower Yarra tributaries, it ranges from very low to moderate.
- Lack of in-stream habitat complexity
Habitat complexity such as submerged wood, rocks and pebbles, and aquatic plants tend to support a greater diversity of macroinvertebrates.
- Urban and rural impacts
Changes to natural stream flows and quality of urban and rural runoff.
- Lack of streamside native vegetation
Removal of streamside vegetation or the presence of weeds and introduced trees (willows) leads to altered leaf fall input, shading, water temperature, food sources and water quality.
- Modified flow
Very high and very low flows can lead to a reduction in habitat availability.
- Loss of wetlands
A reduction in wetlands results in a loss of habitat for species dependent on wetlands.
- Loss of floodplain connectivity
Removing the ability of floodplains to connect to waterways may result in a loss of habitat.
Potential management actions
- Improve streamside habitat
Revegetate streamside zones and weed control (including 'woody weeds' such as willows).
- Protect, enhance and maintain channel and bank habitat
Introduce woody debris to provide habitat, and control erosion including fencing off stock.
- Implement environmental flow regimes
Provide and protect appropriate flows to ensure that macroinvertebrates are protected from loss of habitat.
- Reduce directly connected imperviousness (DCI)
Introduce or increase water sensitive urban design, stormwater treatment.
- Improve water quality in floodplain wetlands
Manage inputs into waterways such as sediment and stormwater.
- Improve water quality in waterways through improvements to rural land management practices
- Increase habitat
Create more floodplain based refuges for wetland species.