Wardang 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
- Reef habitats dominated the biounit and were in variable condition.
- Where seagrass was present it was also variable in condition.
About the biounit
The Wardang biounit extends from Island Point, north of Port Victoria, down the western side of the Yorke Peninsula to Corny Point. The biounit faces west into Spencer Gulf and Wardang Island is offshore from Port Victoria. The biounit is exposed to moderate wave energies, particularly on the outside of Wardang Island, while Hardwicke Bay is relatively sheltered, and may be affected by low flushing.
Wardang has only a small number of coastal towns with the largest being Port Victoria, which, as of 2016 had 352 permanent residents. Population growth within the region has been small since the last census in 2011, with an increase of 36 permanent residents. Sewage treatment from these small coastal towns is via septic tanks, which in sandy soils has the potential to transport nutrients into groundwater and travel towards the coast.
The region is surrounded by agricultural land with cereal crops dominating the entire Peninsula. There are no recognised creeks that regularly flow to the ocean meaning limited agricultural surface runoff.
An investigation of potential threats to water quality for Wardang predicted that it was likely to be in good condition.
A total of 7 sites were monitored in 2016. 40% were comprised of bare sand, 39% reef and 21% seagrass. 2 additional sites, Port Rickaby (m0136) and Wardang Island (m0152) were added to the program since 2010.
Seagrass habitats were generally sparse to moderate in density and patchy in cover. While reef habitats were mostly in poor condition with only one site displaying healthy robust brown macroalgal assemblages.
The AECR assessment indicated that the biounit was observed to be in poor condition which is worse than the predicted condition of good.
This AECR assessed the condition of habitats in waters between 2–15 m deep throughout the Wardang biounit sampled in autumn 2016. There are large areas within the biounit that are deeper than 15 m which are not included as a part of this evaluation.
Reef systems within Wardang were in variable condition, with Port Victoria (m0131), Hardwicke Bay (m0130), and Port Rickaby (m0136) dominated by turfing algae with little to no large brown canopy algae. The outer side of Wardang Island (m0152) was dominated by extensive brown algae (mainly Cystophora spp.) and low abundance of turfing algae suggesting a healthy reef system.
With the exception of Corny Point (m0127), seagrass in Wardang was in poor condition. Generally, sites were similar in composition and condition to 2010 with only Corny Point having dense and continuous meadows of Posidonia spp. Seagrass at Point Souttar (m0128) was a mixed habitat of sparse to moderate Heterozostera spp. and Halophila spp.. These species are known to colonise areas after disturbance, which might suggests an improvement since 2010 when no seagrass was recorded.
Water nutrient concentrations were variable across Warding, with nitrogen being slightly elevated near the township of Port Victoria (m0131) with a maximum total nitrogen of 1.22 mg/L. Turbidity across all sites were below 1 NTU suggesting clear waters.
Pressures and management responses
Coastal development is likely to increase the number and density of septic tanks which contribute nutrients into shallow ground waters that flow to the sea
Development in coastal townships has been slow since the last report, however most new development occurs in subdivisions where stormwater is required to be retained on site via rain water tanks and any overflow is managed through Council’s stormwater disposal system.
Coastal development will increase, however wastewater is disposed of in either Council’s Community Wastewater Management Schemes (CWMS) or disposed of in accordance with the SA Health Commission requirements where soakage trenches are to be located greater than 100 meters from the high water mark to reduce the risk from pathogens.
The Wardang biounit was in poor condition. Habitats throughout this biounit were mixed between seagrass and small algae. In some locations it was unclear whether the habitat had severely degraded or whether we are seeing the beginning of recovery.