Piccaninnie nearshore marine biounit
2015 Aquatic Ecosystem Condition Report
- On the map, zoom in and click on the dots to view underwater video at each site
- The biounit is subject to high wave energy
- Reefs were in good condition with extensive and diverse algal communities
- Seagrass was not observed on any of the sites monitored
- Turbidity was very high at a number of sites and may be impacting on ecosystem condition.
About the biounit
The Piccaninnie biounit is within the Otway Bioregion and spans the area from Cape Northumberland to the Victorian Border. The biounit faces south and experiences the full force of the Southern Ocean resulting in high wave energies.
Limestone reefs are the dominant coastal marine habitat in Piccaninnie and are typically comprised of complex communities of brown, red and green macroalgae supporting a wide range of fish and invertebrates including the southern rock lobster (Jasus edwardii).
The entire southeast region of South Australia is a highly modified landscape. The catchments throughout Piccaninnie have been cleared for agriculture and forestry with very little native vegetation remaining resulting in increased surface water runoff often laden with nutrients and sediments. Agricultural productivity from land adjacent to Piccaninnie is significant for the Southeast which contributes approximately $5 billion to the South Australian economy. The largest coastal town in Piccaninnie is Port MacDonnell, with a relatively small population that swells in holiday periods. There is a large breakwater and harbour at Port MacDonnell that is home to a substantial fishing fleet focused on southern rock lobster.
The Finger Point wastewater treatment plant (WWTP) discharges nutrient rich wastewater into coastal waters slightly east of Cape Douglas in the Nene biounit. However the dominant currents travel west to east which means that nutrient rich water may be transported into Piccaninnie.
The Piccaninnie biounit was predicted to be in Very good condition, based on an assessment of threats to the nearshore habitats.
Eight sites were monitored in waters between 2 – 15 m deep during autumn and spring in 2015 to assess the condition of the Piccaninnie biounit. There are large areas within the biounit that are deeper than 15 m, which are not included as a part of this evaluation.
Sites assessed throughout Piccaninnie were dominated by rocky reefs supporting dense communities of diverse macroalgae.
Overall the findings suggest that the nearshore marine habitats are generally in Very good condition: habitat structure is considered natural, but there are some detectable changes compared to an Excellent condition. The habitat changes are unlikely to be leading to changes in ecosystem function. Any detrimental effects are limited to localised areas and likely to be reversible due to low population, low anthropogenic inputs and high flows from the Southern Ocean.
A total of 74% of the area assessed was classified as reef, 26% was classified as unvegetated sand and no seagrass was observed.
The rocky reefs in the Southeast have had relatively little monitoring compared to locations closer to Adelaide, which has resulted in sparse information about their response to disturbance. More information is required to interpret some of these findings as degradation or if this is the natural state. Further work is needed to develop more detailed conceptual models for this area.
Reef habitats were typically diverse with high cover of canopy algae, while sand occurred in small patches among reefs. Two sites: Cape Northumberland (m0550) and Breaksea Reef (m0551), had consistently less than 40% cover of canopy algae, which may be indicating stress or could be their natural state reflecting high wave energy at those locations.
There are a number of sites close the Finger Point WWTP that may be subject to stress from higher nutrient loads, however high energy from the Southern Ocean provides significant flushing which may dissipate the impacts beyond a local scale.
Across Piccaninnie, nutrient concentrations were very low with soluble nitrogen largely below the limit of detection. Similarly, the phytoplankton and turbidity measurements were also very low suggesting an oligotrophic environment.
Pressures and management responses
|The Finger Point wastewater treatment plant collects, treats and then discharges nutrient rich wastewater to the nearshore marine environment and may be impacting on the ecosystem.||
SA Water monitors its discharges from the Finger Point WWTP to ensure the plant is performing and to enable an assessment of any changes in the discharge which might increase the pressure on the receiving environment. These reports are submitted annually to the EPA for review.
|The township of Port MacDonnell discharges small amounts of urban runoff from drains throughout the town.||Natural Resources SE, on behalf of the Limestone Coast Local Government Association, is currently implementing a large scale on-ground works project focused on improving the quality of coastal habitats along the full length of the coast from the Coorong to the Victorian border. This work includes extensive revegetation along drainage reserves, roadsides and coastal foredunes. This work will focus on coastal dune stabilisation, contributing to beach and dune stability.|
|Agricultural runoff from the catchments discharged through natural watercourses such as Eight Mile creek.||
The SE Natural Resources Management Board have support projects focused on the restoration of coastal wetlands located in the Piccaninnie Biounit and include Picks Swamp and Piccaninnie ponds. The restored wetlands now filter water before flowing to the ocean and Middle point swamp, where the installation of a small regulator has improved the retention of discharge water at the site.
Increasing the amount and quality of remnant fringing vegetation at these sites is assumed to assist in reducing nutrients loads entering wetlands that discharge to the ocean via drains.