Coorong 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
- Seagrass in the south of the biounit is largely dense and continuous, seagrass loss was significant at many of the sites
- Some indicators of nutrient enrichment such as epiphyte loads has disappeared
About the biounit
The Coorong biounit is in the Coorong bioregion and spans the outer western edge of Horseshoe Bay at Port Elliot to Cape Jaffa at the southern end of Lacepede Bay. The majority of coastal waters of the Coorong biounit are high energy with waves rolling over bare sand and breaking onto the sandy beaches of the Younghusband Peninsula. The seafloor gradient decreases in the southern end of the biounit allowing seagrasses to proliferate in the shallow waters of Lacepede Bay while reefs become prevalent at the outer, more exposed areas of the bay.
The towns of Port Elliot, Middleton and Goolwa are adjacent the northern section of the Coorong biounit. The population of these towns are steadily increasing with new permanent residents in the Sea-change movement. Tourists swell the population of these coastal towns during holiday periods. The growing urbanisation and flux of tourists is likely to be increasing stormwater runoff and possible strain on the sewerage systems resulting in more pollutants reaching the marine environment. In the south of the biounit is Lacepede Bay and the coastal towns of Kingston SE, and Cape Jaffa. Urban runoff from these small towns carrying nutrients and sediment reaches the coast during periods of heavy rainfall.
The southeast region of South Australia is a highly modified landscape. Since 1863, broad-scale land clearance has occured and the construction of an extensive cross-catchment drainage system. Dozens of drains discharge nutrient and sediment laden water from agricultural catchments directly to the marine environment. Agricultural runoff contributes nutrients and sediment to the marine environment often in very large volumes and high concentration discharge events.
In 2015 the Canunda biounit was in Very Good condition, based on monitoring conducted over autumn and spring seasons.
A reduced number of sites were monitored in 2021 (10) compared to 2015 (21). For comparable analysis, only sites that were monitored in both years were used to calculate the latest scores. Sites in waters between 2 – 15 m deep were surveyed during autumn 2021 were analysed to assess the condition of the Coorong biounit. There are large areas within the biounit that are deeper than 15 m that are not included as a part of this evaluation.
Seagrass was the dominant habitat of this biounit, with only Basharms Beach containing reef (>90% coverage of the habitat) which is located on the far north-western side of Long bay. Percent cover of total seagrass has reduced by around 12%, with the greatest losses seen in Kingston SE from sites in close proximity to Maria Creek Drain discharge. Epiphyte percent cover has dropped 53% from the 2015 monitoring period, this could be attributed to a number of factors including the South East Flows Restoration Project (SEFRP).
The SEFRP was completed in early 2019, the project objective was to divert a number of drains to enhance flows to wetlands in the Upper South East and the South Lagoon of the Coorong, to help manage salinity levels and enhance ecosystem resilience. Subsequently, this has reduced the amount of surface water and excess nutrients that is being discharged from these drains into the near shore environment.
The nearshore habitats in the Coorong biounit were assessed and remain Very good. Although seagrass percent cover has reduced in areas, reef condition has largely stayed the same. The reduction in epiphyte loads, although not considered in the score, indicates that the biounit is becoming less nutrient enriched and suitable for restoration efforts.
Of the sites monitored, 10% of the habitat was reef, 56% was seagrass and 34% was unvegetated sand. The observed habitats monitored vary from existing habitat mapping, as this monitoring period is using a small number of sites on a large biounit, variation is expected.
Posidonia and Amphibolis were the dominant seagrasses in the biounit, generally they were in good condition, in areas around Cape Jaffa they created dense continuous meadows with very little to no epiphyte loads. A study conducted in 2004/05 (Wear et al, 2006) showed that seagrass in close proximity to Blackford drain, Maria Creek drain and Butchers Gap drain were all under pressures from excess nutrients and had areas where seagrass was lost. The findings from autumn 2021 monitoring period has shown further decline in seagrass percent cover to these areas: Maria South (m0505) showed a 50% loss of total seagrass cover from 2015, Maria (m0560) a 26% loss and Blackford drain (m0545) was down 17%.
Soluble and total nutrient concentrations were consistently low throughout the biounit, total Nitrogen was down 0.015mg/L from 2015. At the time of sampling, Fp ratios have increased significantly at two sites, Maria South (m505) and Maria (m0560). Interestingly, these two sites experienced the greatest loss of seagrass in the biounit. Fp ratios have decreased significantly at Cape Jaffa Jetty (m0525) and Butchers Drain South (m0534). Both sites showed no significant change in seagrass coverage, however, epiphyte percent cover at the two sites has dropped from 70-80% to less than 1%. Hog Lake and Butchers Drain showed similar results. Photopigment sizes of phytoplankton communities, show a decreased abundance in larger micro pigments from sites including Butchers Drain and south-west to Cape Jaffa. Less micro pigments and more nano/pico pigments are characteristics of more oligotrophic conditions. Water chemistry results and epiphyte presence disappearing are indications that sections of the biounit are becoming less nutrient enriched.
One site contained reef habitat in the biounit: Bashams (m0512), it’s structure was low lying reef which was 60% covered by canopy forming big brown algae such as Cystophora spp., and Ecklonia, with the understory comprised of a variety of red algae including Plocammium spp.. The complexity of the algal community, along with low sedimentation is an indicator of good reef health. Reef score for the biounit has remained at Excellent.
The whole biounit was subject to high turbidity, with the highest readings at Bashams beach (2.1 NTU) and Cape Jaffa Jetty (1.6 NTU). It was noted that many sites during the monitoring period had to be visited multiple times to get analysable video footage.
Pressures and management responses
The significant modification and regulation of rivers in the Murray-Darling Basin has resulted in adverse changes to the quality, quantity and hydrological variability of water in the Coorong.
The Department for Environment and Water (DEW) is responsible for the management of South Australia’s water resources and National Parks. Many programs and projects contribute to improving the quality and quantity of water discharged from the Coorong, in particular:
The Murraylands and Riverland Landscape Board (MRLB) are responsible for the ongoing management and review of the River Murray system through two sets of legislative policy aimed to manage water sustainably:
The MRLB also deliver a sustainable irrigation program that provides practical support to irrigators in the Murraylands and Riverland landscape region with the aim of facilitating long-term, sustainable water use of the River Murray. Click here to find out more
Discharge from Southeast agricultural drains brings considerable loads of nutrients to coastal waters.
The District Council Kingston uses stormwater bores in numerous locations throughout the town for its stormwater management rather than discharging to Maria Creek and into the sea.
Flows from the drainage system in the Southern parts of the Coorong depend upon rainfall levels. In drier times, it can be expected that flows from the drainage network to the sea may also decline. The South East Drainage and Wetland Strategy 2019 outlines intentions of the former South East Natural Resources Management Board (now Limestone Coast Landscape Board) and the South Eastern Water Conservation and Drainage (SEWCD) Board to manage moving water in the drainage system. SEWCD is increasingly looking at ways to divert water from drains into wetlands where the water quality is appropriate and where it is possible instead of discharging water into the sea. In addition, a project led by the Limestone Coast Landscape Board in partnership with other stakeholders including the SEWCD Board will explore the feasibility of sourcing drainage network water and storing it underground as managed aquifer recharge instead of draining to the sea outlets. The SEWCD Board is always looking for opportunities to utilise the water in the drainage network for beneficial outcomes, if feasible.
Urban stormwater carries nutrients and pollutants to coastal waters.
District Council of Kingston uses on-site stormwater management using stormwater bores, especially for commercial developments, for example: the recent re-development of BP service station by On The Run demonstrated developer and Council collaboration facilitating storm water infiltration to the grassed road reserve.
All new residential developments in the District Council of Kingston must have rainwater tank with storage capacity of minimum of 22,500 litres for domestic use thus reducing the amount of excess storm water run-off into Council’s storm water table.
At the Cape Jaffa Anchorage marina residential development, each allotment must include on-site overflow stormwater facilities including a filtration trench or similar structure prior to discharge to the street storm water system. Street stormwater system incorporates a swale on the road reserve, which due to the nature of sandy soil absorbs most of the excess run-off.
Septic tank leakage may be reaching the marine environment through groundwater.
District Council of Kingston Development Plan requires that for any development to take place the minimum site level is 2.4 metres AHD (Australian Height Datum) and minimum finished floor level is 2.65 metres AHD. This requirement also applies to the septic tank location and reduces the amount of effluent that may discharge into the ground water and potentially to the sea.
Dredging of Cape Jaffa Marina may increase the amount of suspended sediments in the area
No response provided.
- Download the 2021 habitat and water quality data
- Download the Methods Report for the nearshore marine ecosystems monitoring, evaluation and reporting program.
- South East Flow Restoration Project PDF - https://cdn.environment.sa.gov.au/environment/docs/south-east-flows-restoration.pdf