Port Philip Bay
Port Phillip Bay covers 1,950 square kilometres. While relatively large in area the Bay is shallow with an average depth of 13 metres. The Bay's catchment covers over 9,790 square kilometres in area, and consists of 21 natural drainage basins. The Bay consists of a variety of habitats including sandy seafloor, seagrass beds and rocky reefs. Most of the seafloor is sand and silt which is home to a diverse assemblage of invertebrates. These vast areas of sand are in some parts covered by dense seagrass meadows that provide important habitat for much marine life, especially juvenile fish. Rocky reefs can also be found on some margins of the Bay often being dominated by hundreds of different seaweeds.
The Bay supports:
- approximately 300 species of fish
- several hundred species of molluscs
- several hundred species of crustaceans
- at least 200 species of seaweeds
- several hundred species of polychaetes (bristle worms)
- 2 species of seagrass
- several hundred species of cnidarians (jellyfish, corals, etc)
- several hundred species of sponges
The Bay is of significant social, economic and environmental value to Victoria. Areas of the Bays beautiful and diverse underwater environment are also protected in Marine National Parks and Sanctuaries.
The greatest risks to the health of Port Phillip Bay are from influxes of nutrients and marine pest invasions. The Port Phillip Bay Environmental Management Plan outlines actions to be taken to manage these risks.Port Phillip Bay Environmental Management Plan (EMP)
The Port Phillip Bay Environmental Management Plan (EMP) provides the overarching framework to address two key risks to the Bay's environment: nutrients and marine pests. Among the recognised Bay environmental risks, nutrients and marine pests have emerged as particular priorities. These risks can affect ecological processes both Bay-wide and locally and have ecological impacts that are already, or without action could become, irreversible even with the intervention of technology and science.
The Plan outlines current management objectives to reduce nutrient and marine pest risks, and programs to deal with these risks, and the responsibilities of government agencies. The Background Document to the EMP provides additional information on environmental management arrangements of the Bay.
Performance associated with the EMP is reported on annually. Copies of these annual reports can be found at Port Phillip Bay reports. In 2004, the Central Coastal Board completed its interim review of the PPB EMP's implementation. It can be downloaded from the Central Coastal Board website.
Nutrients - Risk Reduction
The EMP plays an important role in providing a management framework for targeting a 1000 tonne reduction in annual nitrogen loads to the Bay by 2006. This reduction is required by the State Environment Protection Policy for Port Phillip Bay. The focus of nitrogen reduction is on the Western Treatment Plant and catchment waterways.
The EMP also establishes arrangements to monitor the health of processes operating in the Bay's sediments that allow nitrogen, the main nutrient of concern, that enters the Bay to bubble off as nitrogen gas. The 1992-1996 CSIRO Bay study highlighted the importance of this nutrient cycling process and the vital role it plays in balancing the nitrogen budget of the Bay.
A monitoring program is in progress that aims to detect, as early as possible, detrimental changes to critical elements of the Bay's nitrogen cycling processes. Two reports describe the scientific and statistical basis for the monitoring approach.
- Port Phillip Bay Nutrient Monitoring Proposal – Scientific and Technical Advice
- Port Phillip Bay Nitrogen Monitoring Proposal – Statistical Advice.
This monitoring program started in 2002 and the reports describe results so far. The third report provides an overview of the first three years of monitoring.
To further understand the potential effects of nitrogen loads to the Bay, the model developed in the Port Phillip Bay Environmental Study has been used to predict the impact of different nitrogen load scenarios on the Bay;
- Port Phillip Bay Integrated Model Scenarios for Nitrogen Load Reductions and Aquaculture Loads, and
- Port Phillip Bay Integrated Model Scenarios for Large Yarra Floods.
The PPBEMP monitoring program has also been supplemented by the nutrient cycling component of the Channel Deepening Baywide Monitoring Programs (CDBMP). This extends continuous measurements to a fourth site, and makes more highly replicated benthic flux measurements quarterly at two sites, and twice-yearly at a third site. The extended CDBMP monitoring began in December 2007. Reports for the augmented program are published regularly on the Office of the Environmental Monitor's website .
Marine Pests - Risk Reduction
Marine pests threaten the biodiversity and ecological integrity of Victoria's marine ecosystems, pose a risk to human health, and threaten the social and economic benefits derived from the marine environment, including aquaculture, recreational and commercial fishing, and domestic and internal shipping. Arrangements to manage the risks posed by marine pests in Victoria and other coastal States of Australia are outline in the EMP.
The impact of marine pests on nitrogen cycling is also being considered.