On the map, zoom in and click on the dots to view underwater video at each site.
Subtidal habitats outside of Point Longnose were dominated by dense Posidonia spp. seagrass with very low epiphyte loads suggesting that they were reflecting a very low nutrient environment.
Inside Point Longnose the habitats were varied with dense mono-specific beds of the green algae Caulerpa cactoides through to meadows of dense Halophila australis spp. and sites covered in bacterial mats or benthic micro-phytoplankton or globulose algal scum.
There was overwhelming evidence that the habitats inside of Coffin Bay were under stress from nutrient enrichment.
Area map
About the Eyre biounit
The Douglas Biounit is located in the Eyre bioregion and spans the waters between Point Drummond to Point Sir Isaac and includes Coffin Bay. The biounit has a combination of open coasts with variable exposure through to the highly sheltered bays inside Coffin Bay.
Along the rocky exposed coasts and offshore islands, rocky reef habitats are dominant comprising of Cystophora sp, and Ecklonia radiata in deeper waters, with extensive understories of diverse red and green algae. The sheltered environments in the lee of Point Sir Isaac are dominated by extensive Posidonia australis spp. seagrass meadows which transition into Posidonia coriacae in deeper waters. The green alga Caulerpa cactiodes and the seagrass Halophila australis are the dominant habitats in Coffin Bay, which is also characterised by intertidal mudflats and dynamic sand channels. The shallow, sheltered bays in Coffin Bay are likely to result in lower water exchange with the ocean, which can exacerbate the effect of nutrient enrichment.
The Douglas biounit is influenced by upwelling events that occur off the continental shelf during the autumn months. These events bring cold nutrient rich water into nearshore waters which help to drive high productivity of the region. The biounit has large areas of shallow, warm waters which have reduced flushing.
The largest town in the biounit is Coffin Bay with 615 permanent residents and treats sewage through a community wastewater management system and reuses the wastewater for watering the golf course and a wood lot resulting in no discharge to the marine waters. Other townships including Farm beach, Wangary and Mount Dutton Bay use septic tanks to dispose and treat sewage, which in sandy soils, have the potential to introduce nutrients into shallow groundwater. The population of the biounit substantially increases over the holiday periods which is likely to add strain on the capacity of sewage treatment systems and on-site septic systems.
The adjacent land use is a combination of dryland cropping, particularly in the north of the biounit, and native vegetation throughout the Coffin Bay National Park. The waters of Coffin Bay are renowned for oyster aquaculture with extensive leases throughout the intertidal sheltered waters.
The assessment of identified threats to the nearshore habitats predicts that Douglas is likely to be in Good condition.
In summary
The habitats throughout Douglas were varied with habitats outside of Point Longnose dominated by dense and continuous meadows of Posidonia spp. seagrass and complex rocky reef communities at Point Drummond.
Inside of Point Longnose habitats were complex and mixed ranging from dense and continuous meadows of the seagrass Halophila australis and dense meadows of the green alga Caulerpa cactoides and sites covered in bacterial matts, benthic micro-phytoplankton or globulose algal scum.
Findings
The condition of habitats in waters between 2–15 m deep throughout the Douglas 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 habitats outside of Point Longnose were dominated by extensive dense meadows of Posidonia australis spp. seagrass which transitioned into Posidonia coriacae in the deeper sections (eg: m0414: Cliff Hill). The seagrasses outside of Point Longnose were sparsely covered in epiphytes (if at all) and were consistent with a very low nutrient environment. Point Drummond (m0416) was a complex rocky reef dominated by large robust brown algae (including Ecklonia radiata and Cystophora spp.) with dense and diverse red algal communities.
Inside of Point Longnose the habitats were complex and varied with little pattern to their distribution. There were areas with dense meadows of the green alga Caulerpa cactoides including west Coffin Bay (m0408), west of Rabbit Island (m0400) and Bulldog Point (m0409). Dense meadows of Halophila australis spp. were observed east of Rabbit Island (m0404), north of the Brothers (m0402) and west Dutton Bay (m0407). Often the Halophila australis spp. meadows were blanketed in dense epiphytes or opportunistic macroalgae and in spring there were abundant ascidians.
East Dutton Bay (m0406) was a mix of globulose brown algal scum and bacterial matt with abundant jellyfish with occasional patches of dense Halophila australis with dense epiphytes. South of the Brothers (m0405) was a sandy rocky broken bottom with abundant sea urchins (Heliocidaris erythrogramma) and very little algae.
The phytoplankton in the water column was substantially elevated during autumn outside of Point Longnose. This is likely to have been influenced by a major algal bloom in that area in the preceding month. This region is commonly affected by upwellings which transport cool nutrient rich water from the continental shelf into coastal waters during autumn which greatly contribute to the regional productivity, which can also result in algal blooms.
Sites inside Point Longnose typically had higher total nutrients, than sites outside, while Kellidie Bay (m0403) was high in both dissolved and total nitrogen throughout the year. This site was was turbid and had high phytoplankton in autumn, which may reflect its very long water residence times and potential for agricultural runoff from Minniribbie creek, which the EPA found to be in poor condition in 2010.
There is overwhelming evidence to suggest that a number of sites inside Point Longnose are being affected by excess nutrients. Dense epiphytes were observed throughout Halophila australis spp. meadows, frequent observations of the opportunistic alga Hincksia sordida (snot weed) and there were also observations of species that have been used as indicators of nutrient enrichment in other programs eg: dense jellyfish and ascidians. The data suggests that the entire Coffin Bay area is under stress from nutrient enrichment. Unfortunately we do not know the historical composition of the habitats in these locations so cannot definitively state whether the habitats have changed over time as a result of human activity or the current composition is consistent with the historical normal state. While it is likely that upwellings are affecting the region, the enclosed nature of the bays are likely to be exacerbating the effect of excess nutrients. Additionally it is possible that local sources of nutrients are contributing to the degree of stress on the habitats.
This assessment suggests that Douglas biounit as a whole is in Good condition indicating that the biounit is likely to be slightly impaired with symptoms of nutrient enrichment which may cause some initial changes to ecosystem function.
The findings presented here are explained more thoroughly in the Eyre & Murat Assessment Report.
Pressures and management responses
Pressures
Management responses
Agricultural runoff from the Wangary region flowing through the Minniribbie creek is likely bringing nutrients and sediments into the nearshore waters, particularly Kellidie Bay
The Eyre Peninsula NRM Board continues to work with land managers to adopt practices that reduce pollutant loads entering waterway
Urban runoff from Coffin Bay is likely to be introducing nutrients and sediment into nearshore waters.
The Eyre Peninsula NRM have funded the construction of several ‘rain gardens’ which are designed to improve the quality of stormwater from the region.
The District Council is considering the commencement of stormwater monitoring in 2016 to determine the presence of any potential contaminant levels. This data will be provided to the relevant agencies and recommendations developed for any identified treatment options.
Failing and/or high density of onsite wastewater treatment (septic) systems in some coastal towns. Overflowing septic systems contribute nutrients to nearshore marine waters through shallow sub-surface or occasional overland flows.
The District Council of Lower Eyre Peninsula are in the process of undertaking a Development Plan Amendment which will introduce a Community Wastewater Management System to redeveloped Shelley Beach area in Kellidie Bay.