Franklin 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 throughout the biounit were dense and largely continuous.
- Some locations were observed to be under stress due to dense epiphyte loads on seagrass leaves. It is possible that seagrass could be lost if this stress is prolonged
- The enclosed nature of Franklin Harbor is likely to be exacerbating the symptoms of nutrient enrichment
Area map
About the biounit
The Franklin biounit ranges between Cape Driver at Arno Bay through to Victoria Point at the mouth of Franklin Harbor on the western side of Spencer Gulf (see the map). Franklin Harbor has large areas of shallow, warm waters which have reduced flushing with Gulf waters, resulting favourable conditions for algal growth, which is likely to exacerbate the biological effects of excess nutrients
The biounit also has a large oyster industry in the sheltered waters of Franklin Harbor.
The township of Cowell contributes stormwater runoff into Franklin Harbor carrying nutrient and sediments into the nearshore waters after periods of rain. Sewage disposal from the town’s population 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 Franklin 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 Franklin 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 Franklin 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 Franklin biounit was observed to be in Good condition. Seagrass habitats were generally dense and continuous, however within the biounit there were areas that were under stress due to nutrient enrichment; it is possible that habitats may be lost if this stress continues. There was observed to be excessive growth of epiphytes on the seagrass leaves, which if prolonged, can result in impacts on the seagrass over time. It is likely that the enclosed nature of Franklin Harbor is likely to be exacerbating these symptoms at the sites within the Bay.
It is important to note that this report assessed condition of the ecosystem and that these reports do not assess the suitability or quality of waters for aquaculture, food quality and fish health. For details about water quality affecting seafood quality please refer to the South Australian Seafood Quality Assurance Program (SASQAP)
Findings
4 sites were monitored during autumn and spring in 2010 to assess the condition of the biounit; 70% of the habitats monitored were covered in seagrass, while 30% were covered in unvegetated sand. There was no rocky reef or small algae encountered in the sites assessed.
Seagrass coverage throughout the biounit was variable with some areas having dense and continuous seagrass meadows, while one of the sites within Franklin Harbor was found to be bare sand. The unvegetated Franklin Harbour site may be in its natural state or previous seagrass coverage in the area may have been lost; there is insufficient historical information to be certain.
While the seagrass generally dense and continuous, there were numerous indicators suggesting an excess of nutrients. For example there were seagrasses coated in a thick layer of epiphytic algae as well as frequent observations of snot weed (Hincksia sordida) and sea lettuce (Uvla spp.). These indicators were not limited to inside the enclosed Franklin Harbor where the symptoms can be exacerbated but also at the more open waters of Arno Bay.
The findings suggest that the nearshore marine habitats are generally in Good condition, however there are parts of biounit under stress due to the excess of nutrients.
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 |
---|---|
Sea cage aquaculture is undertaken in nearshore waters adjacent to Arno Bay which introduces nutrient loads into the nearshore marine waters |
The South Australian Research and Development Institute (SARDI) is preparing a report titled “Carrying Capacity of Spencer Gulf: Hydrodynamic and Biogeochemical Measurement, Modelling and Performance Monitoring”. This will investigate the transport and fate of nutrients within this region which can be used to manage the location and management of sea cage aquaculture throughout the Lower Spencer Gulf. The Aquaculture (Zones – Port Neill) Policy 2008 and the Aquaculture (Zones – Arno Bay) Policy 2011 limits the maximum biomass of sea cage aquaculture animals that can be grown in the zoned areas and is based on a carrying capacity model to determine the suitable amount of fish for each particular region without causing adverse environmental impacts. When assessing an individual licence application there is a strict set of guidelines that applies a semi-quantitative risk-based assessment, based on a nationally accredited Ecological Sustainable Development assessment framework (Fletcher et. al., 2004), to determine the sustainability and outcome of each individual application. The integrity of the assessment process rests on understanding both the nature of the environment in which aquaculture is practised and the manner in which aquaculture interacts with or changes the environment that surrounds it. This includes assessment of approximately 40 possible risk events considered directly relevant to potential aquaculture influences, and applies them on both site and regional levels. PIRSA also apply guidelines to minimise environmental harm by excluding aquaculture over areas of seagrass, reef and macroalgae considered significant to local ecology. Annual Environmental Monitoring Program (EMP) proformas are required to be submitted by all licence holders for each licensed site for each reporting year. These are reviewed (by PIRSA and EPA) prior to being sent out to licence holders to ensure appropriate information is being collected. Current data collected and assessed in EMP reports includes:
Annual Environmental Monitoring Program (FEMP) Environmental Monitoring Program sampling is conducted by the South Australian Research and Development Institute (SARDI). This program involves sampling sediment adjacent to actively farmed sites and using DNA profiling to measure changes in the benthic community compared to established control sites. PIRSA Fisheries and Aquaculture, the finfish industry and SARDI determine which sites are to be sampled each year. The same group has responsibility for any follow up action that needs to occur as a consequence of poor results through the 10-point FEMP plan of action. |
Failing and/or high density of onsite wastewater treatment (septic) systems in some coastal towns. This is probably most significant in Arno Bay and Cowell. Overflowing septic systems contribute nutrients to nearshore marine waters through shallow sub-surface or occasional overland flows. The nutrient status within Franklin Harbour is naturally elevated by the natural geomorphology (refer to the report). Therefore there is limited tolerance for additional nutrient input via wastewater discharge. This needs to be considered when planning management strategies for wastewater treatment. |
District Council of Franklin Harbour The Council is considering a community wastewater management scheme for Cowell and this will be located approximately 3km inland to minimise potential for marine impacts. This will help to improve Franklin Harbour water quality. The Council currently operates a small community wastewater management scheme for some shacks in the Arno bay area. Council is evaluating the feasibility of a larger scheme to include the whole town. The treated wastewater will be used for sub-surface irrigation around the local parks and gardens. |
The land based aquaculture facility at Arno Bay discharges wastewater into a small tidal creek which flows to the nearshore marine waters. | As part of the licensing requirements, all aquaculture licence holders must complete and submit an annual environmental monitoring report to PIRSA, detailing (where relevant to that industry) monthly record of biomass of stock on site and feed inputs, incidences of disease, chemical use, water discharge, infrastructure development etc. In addition, under the Aquaculture Regulations 2005, water quality sampling is required by land-based sites that discharge water into state waters. This information allows Primary Industries and Regions SA to assess compliance to licence conditions and potential impacts to the environment. |
Oyster aquaculture within Franklin Harbor will remove phytoplankton from the waters but will deposit organic material into waters under the structures. |
Primary Industries and Regions SA research has indicated that sedimentation due to oyster waste production has negligible impacts to the surrounding environment (see Wear et al 2004). Wear, R., Theil, M., Bryars, S., Tanner, J. and de Jong, S. (2004). Environmental risk assessment of intertidal shellfish aquaculture in South Australia. South Australian Research and Development Institute (Aquatic Sciences). Adelaide. SARDI Publication No. RD04/0155. 75 pp |
Further information
- Download the 2010 habitat and water quality data
- Download the Methods Report for the nearshore marine ecosystems monitoring, evaluation and reporting program.
- Wear, R., Theil, M., Bryars, S., Tanner, J. and de Jong, S. (2004). Environmental risk assessment of intertidal shellfish aquaculture in South Australia. South Australian Research and Development Institute (Aquatic Sciences). Adelaide. SARDI Publication No. RD04/0155. 75 pp.
- Fletcher, W.,J. Chesson, J., Fisher M., Sainsbury, K.J., Hundloe, T., Smith, A.D.M. and B. Whitworth (2002) National ESD Reporting Framework for Australian Fisheries: The 'How To' Guide for Wild Capture Fisheries. FRDC Project 2000/145, Canberra, Australia. 120pp.