Franklin Nearshore Marine Biounit
2016 Aquatic Ecosystem Condition Report
On the map, zoom in and click on the dots to view underwater video at each site
- Seagrass habitats throughout the biounit were variable, some were dense and continuous, but others were sparse or totally absent of seagrass.
- A comparison to the 2010 assessment shows sites outside of the harbor improved, increasing in seagrass cover.
- Franklin Harbor is an enclosed embayment, which limits the flushing of water. This may exacerbate nutrient enrichment.
About the biounit
The Franklin biounit ranges from Cape Driver at Arno Bay through to Victoria Point at the mouth of Franklin Harbor on the western side of Spencer Gulf (see map). Within this biounit is Franklin Harbor, which has large areas of shallow, warm waters with reduced flushing with Gulf waters. This results in favourable conditions for algal growth, exacerbating the effects of nutrient pollution.
Cowell is a small township with a population of 1109 people on the shores of Franklin Harbor. Stormwater from the town runs into waters carrying nutrients and sediments after rain, while sewage disposal from the town’s population is primarily onsite sewage treatment (septic tanks). A community waste management system (CWMS) has been implemented since the previous monitoring period to reduce the overflow of waste and reduce the discharge of nutrients into the shallow groundwater. These systems are put under significant pressure during holiday periods when the town’s population swells. Groundwater is likely to flow towards the coast transporting nutrients into coastal waters.
The adjacent terrestrial environment is highly modified for agricultural use, however there are very few creeks which flow into the marine environment even during large rain events.
Aquaculture at Arno Bay is a significant industry, with Southern Bluefin Tuna (Thunnus maccoyii) and Yellowtail Kingfish (Seriola lalandi) held at a large land based hatchery and sea cage grow out in the adjacent waters. The biounit also has a large oyster industry in the sheltered waters of Franklin Harbor.
Franklin Harbor is a large, warm, shallow, enclosed waterbody with reduced flushing with Gulf waters. These conditions result in a favourable environment for algal growth, increasing the effects of nutrient enrichment.
Based on the threats outlined above, the Franklin biounit was predicted to be in Good condition.
In 2016, l Franklin was observed to be in Good condition. The condition of habitats were variable, with bare sand and sparse seagrass within Franklin Harbor, to dense seagrass along the eastern Spencer Gulf.
In comparison to 2010, there was little change over time within Franklin Harbor, but sites in more open water outside the Harbor had higher seagrass cover than in 2010.It is important to note that this report assessed condition of the ecosystem and 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)
Of the area monitored in 2016, 47% of habitats were seagrass, while 51% were unvegetated sand, and only 2% rocky reef.
Seagrass throughout the biounit was variable, sites within Franklin Harbor comprised of bare sand and small areas of sparse seagrass with moderate epiphyte load on seagrass leaves. This low seagrass cover is consistent with observations in 2010.
Outside Franklin Harbor sites were moderate to dense seagrass meadows. Many sites showed increases in seagrass cover between 2010 and 2016, with Arno Bay increased by almost 15% over 5 years.
As outlined above, Franklin Harbor is a large, warm, shallow, enclosed waterbody with reduced flushing with Gulf waters. These conditions result in a favourable environment for algal growth, increasing the effects of excess nutrients such as epiphyte load.
Water chemistry was similar between sites suggesting the region is well mixed. Turbidity was higher within Franklin Harbor compared to outside, and with little difference between sites. The longer residence time of water inside the Harbor provides favourable conditions for algal growth, which explains higher phytoplankton and epiphyte loads and at Cowell Inner (m0120).
The findings suggest that the nearshore marine habitats in the Franklin biounit are generally in good condition, however it is likely that habitat structure and function are slightly impaired with initial symptoms of nutrient enrichment compared to a system in Excellent condition.
Pressures and management responses
Sea cage aquaculture is undertaken in nearshore waters adjacent to Arno Bay which introduces nutrient loads into the nearshore marine waters
The PIRSA Fisheries and Aquaculture Division is responsible for the regulation of the Aquaculture industry in South Australia.
The Aquaculture (Zones–Arno Bay) Policy 2011 limits the maximum biomass of sea cage aquaculture animals that can be grown in the zoned areas located within the biounit and is based on a carrying capacity model to determine the suitable amount of fish for each particular region without causing significant adverse environmental impacts.
When assessing an individual licence application there is also a strict set of guidelines that applies a semi-quantitative risk-based assessment, derived from a nationally accredited Ecological Sustainable Development assessment framework (Fletcher et al 2004), to determine the sustainability and outcome of each individual application. 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 yearly by all licence holders for each licensed site for each reporting year, including all finfish sites located within the biounit. Data collected is used to adaptively manage the aquaculture industry in South Australia.
Finfish Environmental Monitoring Program (FEMP) sampling is also 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. This sampling to date has not shown a significant difference between farmed sites and control sites within the biounit.
SARDI have also completed a report titled 'Carrying Capacity of Spencer Gulf: Hydrodynamic and Biogeochemical Measurement, Modelling and Performance Monitoring', which was released in 2015. This investigated the transport and fate of nutrients within this region which can be used by PIRSA to manage the location and management of sea cage aquaculture throughout the Spencer Gulf.
Oyster aquaculture within Franklin Harbor will remove phytoplankton from the waters but will deposit organic material into waters under the structures.
The area occupied by oyster leases within Franklin Harbor is capped through the District Council of Franklin Harbour Development Plan, which encompasses the adjacent Harbor. Leasing and licencing activities as outlined for finfish previously apply to the oyster industry occurring in Franklin Harbour, including the requirement for annual EMP reports for the oyster sites located within the biounit.
A research project is currently being conducted by SARDI to determine the component of phytoplankton oysters remove from the water column, in addition to other filter feeding organisms to inform future carrying capacity assessments for this and other aquaculture sectors.
Primary Industries and Regions SA research has also indicated that sedimentation due to oyster waste production has negligible impacts to the surrounding environment (Wear et al 2004).
Failing and/or high density of onsite wastewater treatment (septic) systems in some coastal towns.
District Council of Franklin Harbour has implemented a community wastewater management scheme in Cowell to reduce amount of septic overflow.
Poor agricultural land management practices can result in sediment and nutrient rich runoff entering coastal waters
Eyre Peninsula NRM Board is working with landholders to increase efficiency of fertiliser application; to fence off and restore riparian habitats increasing buffering capacity; and manage stock grazing pressure in riparian zones.
- 2016 habitat and water quality data
- Methods report for the nearshore marine ecosystems monitoring, evaluation and reporting program.
Wear R, Theil M, Bryars S, Tanner J and S de Jong 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