On the map, zoom in and click on the dots to view underwater video at each site.
Seagrass meadows close to the townships of Streaky Bay, Smoky Bay and Ceduna were dominated by moderate to dense Posidoina spp. with high epiphyte.
Habitats in more open water were variable, consisting of moderate to dense seagrass with minimal epiphyte cover, bare sand and rocky reef.
Rocky reefs were comprised of dense canopies of large brown algae, with diverse red and green fine branching algae filling out the understory.
Area map
About the Biounit
The Streaky Biounit is located in both the Murat and Eyre bioregions and reaches from Point James through to Cape Bauer near Streaky Bay. The biounit includes the towns of Ceduna, Smoky and Streaky Bays.
Streaky is typically low wave energy due to the shelter provided by St Peters and Eyre islands with these sheltered bays are dominated by seagrasses particularly Posidonia, Heterozostera and Halophia species. There are scattered stands of the grey mangrove Avicennia marina which provide vital nursery habitat for local fisheries, particularly throughout Davenport creek, which are the most westerly mangroves in South Australia. Streaky has large areas of shallow, warm waters which are likely to have reduced flushing with the open ocean. This results in favorable conditions for algal growth, exacerbating the effect of excess nutrients.
Cumulatively, the townships of Ceduna Smoky Bay and Streaky Bay have approximately three thousand residents and all towns have adequate sewage treatment plants to treat waste. These plants recycle treated wastewater for watering of council’s gardens along the foreshore, golf courses and ovals, with any excess evaporating so that there is no discharge to the marine environment.
The land use adjacent to the biounit is primarily cereal and modified pasture crops, and there are also numerous coastal conservation parks which can act to buffer surface runoff. Given the very low rainfall of the area, surface water runoff from agricultural land is likely to be minimal.
The port of Thevanard exports grain and salt for the majority of the western Eyre peninsula and averages a vessel every 3 days. The grain terminal has the potential to introduce grain dust into the marine environment during loading which can result in nutrient enrichment of the downwind environments.
Oyster aquaculture of the Pacific oyster (Crassostrea gigas) is a major industry for the region and the intertidal oyster farms are spread throughout Denial, Smoky and Streaky Bays.
The assessment of identified threats to the nearshore habitats predicts that the Streaky biounit is likely to be in Good condition.
In summary
The sites monitored throughout Streaky displayed a wide variety of habitat types including seagrass, reef and sand. Seagrass habitats varied from continuous dense meadows in the sheltered bays, through to moderate to sparse meadows in areas of higher energy and in some cases were mixed with rocky reef communities.
Seagrasses that were located close to townships supported higher epiphyte and opportunistic algal loads (eg: Hincksia sordida), which is likely to be due to their proximity to potential nutrient sources, however these locations were also subject to low water flow which can exacerbate the effect of nutrient enrichment.
Findings
The condition of habitats in waters between 2–15 m deep throughout the Streaky Biounit was assessed based on monitoring data collected during autumn and spring 2014. There are some areas within the biounit that are deeper than 15 m which are not included as a part of this assessment.
The Streaky Biounit displayed a wide variety of habitats including seagrass, reef and sand. Typically the sites that were located in the shelter of embayments or behind islands were found to have dense and continuous Posidonia australia spp. seagrass. When the exposure increased the seagrass transitionned to sparse to moderate in cover and also frequently interspersed with rocky reef.
Sites that were located close to towns were covered in a dense blanket of epiphytes and opportunistic algae which is likely causing stress on the seagrass by blocking light reaching the seagrass. This was particularly evident at Point Gibson (m0428), Murat Bay (m0448) and Pigface Island (m0429) in both autumn and spring, and Smoky Bay (m0438) in spring. It is possible that the proximity to nutrient sources from the townships and low water movement in shallow water provide optimal conditions for algal growth especially the filamentous brown algae (Hincksiasordida) which are often indicators of nutrient enrichment.
The more exposed parts of the biounit were often dominated by rocky reef habitat typically comprised of large brown canopy alga Eckloniaradiata and Cystophora spp. or Sagassum spp. dominant, particularly outside Dashwood Rock (m0430). The understory of red (Plocamium spp.) and green (Caulerpa spp.) fine branching algae appearing consistently among all reef systems.
The northern part of the biounit showed elevated phytoplankton in the water during autumn with Murat Bay north (m0448) and Ceduna (m0447) recording above 2.5 µg/L which is approximately three to four times the biounit average. This finding is not surprising given the regions reputation as a prime oyster farming region, which feed on this elevated phytoplankton. Interestingly this increase was not observed during spring with very low concentrations of phytoplankton and nitrogen in the water, but dense epiphytes and opportunistic algae recorded at sheltered sites during this time. This may suggest a seasonal transition from a phytoplankton dominated system to a macroalgal dominated one, which may have an influence on the oyster farming at these times.
The scale of epiphytes and opportunistic algae at the sheltered sites, particularly during spring, suggests that parts of the biounit are likely to be under stress from nutrient enrichment. Many of these areas were very shallow so it is possible that habitats at these locations are still gaining sufficient light to persist, however this may affect the deeper margins of the meadows.
This assessment indicates that Streaky is likely to be in Very good condition. Habitats are considered largely natural but there are likely to be some initial small changes compared to an unimpacted state, but these are unlikely to lead to changes in ecosystem structure or function.
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)
Pressures and management responses
Pressures
Management responses
Urban runoff from the small townships can bring nutrients and sediments into nearshore waters
District Council of Ceduna has installed two gross pollution traps and oil and sediment traps in the Ceduna foreshore stormwater system and is looking to install more as funding permits
Failing and/or high density of onsite wastewater treatment (septic) systems in some coastal townships. Overflowing septic systems contribute nutrients to nearshore marine waters through shallow sub-surface or occasional overland flows.
District Council of Ceduna has upgraded most of its Community Wastewater Management Scheme (CWMS) pump stations to include extended storage (8 hours+) and has backup generator available to run pump stations in event of extended power failure. This is expected to reduce the risk of overflow.