Wardang Nearshore Marine Biounit
2010 Aquatic Ecosystem Condition Report
Condition overview
Key points:
- On the map, zoom in and click on the dots to view underwater video at each site.
- Seagrass habitats monitored throughout the biounit were variable with the majority being sparse to moderate and patchy
- Seagrasses were covered in dense epiphytes suggesting excess nutrients which may affect seagrass health over time
- Small algal communities represented 15 % of the monitored area which is unable to be classified
Area map
About the biounit
The Wardang biounit extends from Island Point just north of Port Victoria down the western side of the Yorke Peninsula to Corny Point. The biounit faces west into Spencer Gulf and has Wardang Island offshore from Port Victoria. The biounit is exposed to moderate to high wave energies, particularly on the outside of Wardang Island, through to moderate to low energies towards Hardwicke Bay.
The Wardang biounit has only a small number of towns with the largest being Port Victoria, which in 2010 had 316 permanent residents. The region is surrounded by agricultural land with cereal crops dominating the entire Peninsula.
Sewage disposal in coastal townships is primarily through on-site sewage treatment (septic tanks) which are likely to discharge nutrients into the shallow groundwater flowing towards the nearshore marine environment.
The Wardang biounit has large areas of shallow, warm waters which have reduced flushing. This is likely to result in favourable conditions for algal grow that could increase the biological effects of excess nutrients.
The Wardang biounit was expected to be in Good condition, based on an assessment of threats to the nearshore habitats.
In summary
The condition of habitats in waters between 2 – 15 m deep throughout the Wardang biounit was assessed based on monitoring data collected during autumn and spring 2010. There are large areas within the biounit that are deeper than 15 m which are not included as a part of this evaluation.
The monitoring results indicated that the biounit was in Poor condition which is worse than the predicted condition of good. The seagrass habitats monitored were generally sparse to moderate and patchy in cover.
The seagrass habitats monitored throughout the biounit were found to be under significant stress due to nutrient enrichment. There was observed to be excessive growth of algae on the seagrass leaves (epiphytes), which if prolonged, can result in the seagrass dying over time.
In some locations it was unclear whether the habitat had severely degraded or whether the current condition is a natural state. Further research is needed to define a condition gradient of small algal communities in these areas.
Findings
5 sites were monitored during autumn and spring in 2010 to assess the condition of the biounit; the sites sampled were a mixture of bare sand (39%), seagrass (25%), and areas of small algae (36%).
The results showed that seagrass coverage throughout the biounit was poor with the seagrass in the biounit that was present was sparse to moderate in density and patchy in cover. The site m0129: Point Pearce was dominated by a small algal community which was unable to be classified using the conceptual models due to a lack of knowledge about small algal communities and how to determine their condition and uncertainty about whether this may have supported large brown canopy algae which has been lost.
These findings suggest that the nearshore marine habitats were variable and in some circumstances do not fit the conceptual models used to classify ecosystem condition. In some locations it was unclear whether the habitat had severely degraded or if the observed condition is a natural state - habitats can be naturally mixed and patchy which limits our ability to judge condition in some circumstances. Further research is needed to define a condition gradient of small algal communities in these areas.
In addition to the degraded seagrasses that was observed, there were numerous indicators suggesting an excess of nutrients, including dense seagrass epiphytes coating the seagrass observed during both autumn and spring sampling events.
The evidence clearly shows that seagrass within this biounit is under stress from excess nutrients due to dense epiphyte loads and opportunistic macroalgae. On going stress to these marine habitats could result in habitat loss. If habitats are lost there could be:
- Impacts on the productivity of fisheries
- Increased erosion and sand movement on beaches
- Reduced wave attenuation along the coast
- A negative impact on marine biodiversity.
Pressures and management responses
Pressures | Management responses |
---|---|
Failing and/or high density of onsite wastewater treatment (septic) systems in some coastal towns. This is probably most significant in the Port Victoria, Hardwicke Bay areas. Overflowing septic systems contribute nutrients to nearshore marine waters through shallow sub-surface or occasional overland flows. |
The District Council of Yorke Peninsula has established Community Wastewater Management Schemes (CWMS) to service the shacks at Collins Beach, Point Turton, Hardwicke Bay and Bluff Beach. The CWMS at Bluff Beach was also extended and connected to other existing freehold properties. Subdivisions constructed in Point Turton and Port Victoria included the development of CWMS. The Council will investigate future expansion of these schemes. Council also encourages existing shack owners on small allotments within 100 meters of high water mark to install Holding Tanks. |
Further information
- Download the 2010 habitat and water quality data
- Download the Methods Report for the nearshore marine ecosystems monitoring, evaluation and reporting program.