Piccaninnie Nearshore Marine Biounit
2021 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
- Reef condition score has not changed
- 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 $3.5 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.
During the Autumn 2015 monitoring period, the Nene biounit was given an ecosystem condition score of Very Good based on the monitoring conducted.
A reduced number of sites were monitored in 2021 (4) compared to 2015 (8). For comparable analysis, only sites that were monitored in both years were used to calculate the latest scores. Video analysis of sites from waters between 2 – 15 m deep during autumn 2021 was used 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. There was no seagrass observed in this biounit which is consistent with State and National data.
The findings suggest that the condition of the Piccaninnie biounit has largely stayed the same since last monitoring period. Reef health indicators such as canopy forming brown algae have slightly improved across the biounit from 2015, although an increase, scores have remained at Very Good.
Four sites were monitored in the Piccaninnie biounit, with 86% of the habitat classified as reef, sand accounted for 14%, no seagrass was recorded.
Reef habitats were typically diverse with high cover of canopy algae, while sand occurred in small patches among reefs. All sites had greater than >50% coverage of large canopy forming brown algae and have shown increases of up to 36%. In 2015, two sites: Cape Northumberland (m0550) and Breaksea Reef (m0551), had consistently less than 40% cover of canopy algae, Cape Northumberland has increased by 10% and Breaksea Reef has increased by 36%. Stony Point (m0554) has shown a 27% increase in canopy forming algae.
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.
Across Piccaninnie, water chemistry showed that organic and dissolved nutrients were slightly elevated from 2015 monitoring, although higher it is not a sign of nutrient enrichment as the biounit is subject to high wave energy aiding in mixing and reducing resident times. Phytoplankton community structures (using Fp ratios and size classes) has shown that the amount of micro pigments present at Stony Point and Breaksea Reef have reduced since 2015 and smaller pigments such as nano and pico are more prevalent. This is an indication that the waters of Piccaninnie biounit are oligotrophic
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.
In accordance with its EPA licence, 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.
SA Water plans to upgrade infrastructure at the Finger Point including improvements in sludge management processes which will assist in maintaining the quality of treated water being discharged as well as an upgrade to the nearshore outfall to aid dispersion and mixing
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.