What are ecosystems?
An ecosystem, short for 'ecological system', is made up of living components such as animals and plants, non-living components like air and water and the interactions that occur between these components (e.g. nutrient cycling).
What are the threats to ecosystems?
Ecosystems vary in their ability to remain unchanged when faced with disturbance (ecosystem resistance) and their ability to return to normal if they are changed (ecosystem resilience). Ecosystems with lower levels of resistance and resilience can be threatened more easily than those with higher levels.
Serious threats include invasive aquatic pests, illegal fishing, nutrients from stormwater runoff, increased sedimentation, industrial spills and contaminated groundwater. These threats can disturb an ecosystem, changing the natural balance that has evolved over time.
Within the bay, there are a series of marine parks and sanctuaries ranging from near pristine systems at the bay entrance to coastal reefs, which are impacted by water flows from the Yarra River and Western Treatment Plant. Overall, Port Phillip Bay can tolerate some disturbance and still remain a healthy and productive ecosystem.
Ecosystem threats vary within the catchments surrounding Port Phillip Bay, but may include stormwater and excess nutrient loads. However, waterways in forested areas generally face fewer impacts than those in agricultural and urbanised regions.
What kinds of ecosystems are found in the surrounding waterways flowing into the Port Phillip catchment?
There are some 8,000 kilometres of rivers and creeks, more than 900 wetlands and more than a dozen estuaries within the Port Phillip catchment.
- Estuaries are semi-coastal waters where freshwater flows from catchments to merge with marine waters. They have a range of salinity, from nearly all fresh water to fully marine, lower wave energy than the open coast, and their floors are generally covered in soft sediments.
- Lowland rivers and creeks are generally more turbid, warm, slow-flowing waters with fine sediment beds. Species found in lowland rivers include fish and invertebrates (e.g. fly larvae, aquatic beetles, water boatman and freshwater shrimp) with broad temperature tolerances and resilience to low oxygen levels. These species live around fine sediments or alternative habitats such as submerged woody debris or aquatic plants.
- Upland rivers and creeks are fast flowing waterways that drain from elevated or mountainous areas, often onto broad deposited plains (where they become lowland rivers). Rivers with a course that drops in altitude rapidly will have faster water flow. This in turn produces the other characteristics of an upland river, such as: a river bed dominated by bedrock, boulders and cobblestones, high dissolved oxygen levels and cooler water temperatures. Upland rivers and creeks are also usually less disturbed by human activity and provide habitat for fish and invertebrate species (e.g. dragon fly, mayfly and stonefly larvae) which are often highly adapted to life in these sensitive ecosystems.
- Lakes are regarded as still water ecosystems, however minor currents can be created by inflowing rivers and creeks or by wind action. Lakes can be reasonably deep with sunlight not able to reach the entire lake bed. Lake edges are usually shallow enough for aquatic plants to grow, which in turn offers habitats for many lake fish and invertebrate species.
- Wetlands are shallow still water ecosystems which can be permanently or seasonally filled. The factor that distinguishes wetlands from other water bodies is the characteristic vegetation that is adapted to its unique soil conditions and seasonal fluctuations in water levels. Wetlands consist primarily of soil saturated with water, which supports aquatic plants and a wide variety of birds, frogs and insects.
Yarra Bend Park. Image source: Parks Victoria
What kinds of marine ecosystems are found in Port Phillip Bay?
Port Phillip Bay has a rich variety and wonderful diversity of ecosystems. The boundaries between different underwater environments are not always clearly defined, with many ecosystems grading into one another or having interesting transitional zones. Different substrate types (material on the sea floor) may also be patchily distributed, therefore providing unique environmental niches for marine species to flourish.
Closest to the coast are marine and estuarine intertidal zones (the area that is above water at low tide and under water at high tide) which include:
Further from the shore are sub tidal habitats (below the low tide mark and always submerged in water) which include:
Above the seabed in deeper waters there is also an area of open water known as the pelagic zone (neither close to the bottom nor near the shore).
Local ecosystems can vary from one another due to variable influences such as water depth, substrate type, wave exposure, temperature, salinity and penetration of light. Marine ecosystems can also naturally change in accordance with diurnal (day – night) or seasonal changes.
For more information please refer to the Taxonomic Toolkit for Marine Life of Port Phillip Bay.
How are ecosystems being managed in the Port Phillip Bay catchment?
The ecosystems of our bay and waterways in the Port Phillip region balance the pressures of an expanding urban landscape and increasing uses of the environment for social, cultural and economic requirements.
Melbourne Water and Parks Victoria have recently developed a values assessment approach that recognises the natural assets in the region. For further Information please refer to the Parks Victoria Marine Natural Values.
Melbourne Water’s research and public consultation also indicates that seven key values are the main reasons that the community wants to protect and improve waterways: amenity, birds, fish, frogs, macroinvertebrates (or bugs), platypus and vegetation.
By assessing the condition of key values over time, it can be understood whether management actions have been successful in improving conditions that support waterway and bay health.
Aspects of waterway condition are: water quality, habitat and flows which are critical to supporting these key values.
For further Information please refer to the Melbourne Water Healthy Waterways strategy.