The Tiparra biounit spans from Point Riley just north of Wallaroo, down to Island Point just north of Port Victoria on Yorke Peninsula (see map). The shoreline of the biounit has a westerly orientation generating low to moderate wave energies.
There are numerous coastal towns on the shores of the Tiparra biounit, with Wallaroo being the largest with 4,426 people (2021 census), an increase of just under 500 people in 5 years. Other significant towns are Moonta Bay and Port Hughes with a combined population of 3,280 people.
The region is subject to substantial coastal development with many new dwellings and new large residential estates around these existing towns. This development can lead to stormwater management issues from increased impervious surfaces (roads and roofs) and coastal erosion from the destabilisation of land at commercial development sites.
The development of the new wharf also has the potential to create further coastal erosion through destabilisation of land, changing hydro-morphology of the area and increased boating/shipping creating more wash. Since 2016, the District Council of the Copper Coast has started to implement a stormwater management plan, aimed to minimise the danger and damage from flooding to the community and the impacts of run-off on the receiving waters.
Most areas have moved away from on-site disposal systems are connected to community wastewater management system, reducing the risk of pollution to the coast. Two new wastewater treatment plants have been built − one at the upgraded Wallaroo facility and the other at Port Hughes.
This region is dominated by cereal cropping and there is a large port facility at Wallaroo to export grain. Approximately 1 km southwest of the current port facility, works are underway to build a new grain export terminal.
The area is also home to a large prawn fishing fleet, which resides in a marina associated with an extensive residential development. During the prawning season, trawlers anchor in Moonta Bay damaging the benthic habitat. Up to 30 trawlers have been seen anchored at a time, some washing down equipment and decks into the bay adding to the nutrient load.
An evaluation of potential threats to water quality predicted that the biounit was likely to be in Good condition.
In summary
In autumn 2022 a total of 6 sites were monitored to assess the condition of the Tiparra biounit. Cape Elizabeth (m0133) was replaced with Cape Elizabeth South (m0146), this was the first time this site has been monitored. All sites containing seagrass habitat within Tiparra biounit experienced a gain in percent cover. Total seagrass percent cover has increased to return to similar cover reported earlier in 2010. Sites that contained reef that were monitored both years remained stable. The new reef site has impacted the overall condition of reef habitat in the biounit. For comparable analysis only sites that were assessed each year were used for score development. The score for Tiparra has remained as Good.
Findings
The condition of habitats in waters between 2–15 m deep throughout the Tiparra biounit was assessed based on monitoring data collected during autumn 2022. Areas within the biounit deeper than 15 m are not included as a part of this assessment. Of the habitat monitored, 27% was reef, 43% was seagrass and the remainder 30% was bare sand.
When comparing sites that were assessed both years, there was an increase of around 20% in the total percent cover of seagrass from 2016. This was largely driven by Moonta Inner (m0132), Moonta Bay (m0134) and Wallaroo (m0135) as these sites contained dense continuous Posidoina spp meadows. Epiphyte loads have increased at every site, with tripling of loads throughout the biounit.
North Beach (m0149) was the only site in which the habitat was quite variable; Posidonia spp.,Halophila spp. and Zostera spp. were observed, but total seagrass was less than 20% of the habitat. Posidonia spp. is now present and there has been an increase in the percent cover of Halophila. Although diverse in seagrass species, this site reflect a system with a disturbance gradient of Very Poor. Bioturbation in the sediment has increased from 2016 along with epiphyte loads on seagrass. The presence of microphytobenthos can be seen throughout the site, along with nutrient enrichment indicator species like European fan worms (Sabella spallanzanii). Phytoplankton community composition shows that Fp ratios have increased, and larger chlorophyll pigments are now prevalent indicating the system has changed from oligotrophic to mesotrophic conditions.
Cape Elizabeth Inner (m0145) remained largely unchanged from 2016 monitoring. It was dominated by big browns and small reds (Asparagopsis spp.), had low sedimentation and low amounts of turfing algae, and the presence of opportunistic algae has been recorded for the first time.
Cape Elizabeth Outer (m0146) which is just outside of the SSG Eastern Marine Park, displayed very similar reef structure to Cape Elizabeth Inner. However, algal communities established on the reef were quite different with turfing algae and small reds being the dominant species. This may be the natural state of this reef or impacts from fishing may be observed. Biodiversity in algal communities can be lost with the removal of fish species that usually garden reefs and control turfing algae.
Phytoplankton community composition throughout the biounit (with the exception of Cape Elizabeth Outer (m0146)) showed that bioavailable nutrients have increased considerably. This coincides with increases in epiphytic load on seagrass, increased turfing algae on reefs and the presence opportunistic algaes. At the time of sampling, water chemistry showed nutrient levels were consistently low across the biounit, with the exception of m0145 which had slightly elevated levels of nitrogen and phosphorus.
Pressures and management responses
Pressures
Management responses
Stormwater runoff from the coastal towns discharges nutrient and sediment loads to the nearshore waters
The District Council of the Copper Coast is systematically improving the stormwater discharge points within their jurisdiction. The significant upgrade to the Rossiters Rd and Otago Drive discharge points are major achievements. Grants obtained from the NRM will see further improvements to two discharge points utilising vegetation to improve the quality of the discharged water. The main Wallaroo discharge point (Office Beach) has been improved with a significant upgrade planned in conjunction with the development of the old Pivot site.
Coastal development is likely to increase the number and density of septic tanks which will contribute nutrients into shallow ground waters which will flow to the sea
Moonta and Wallaroo now have modern sewerage systems with sufficient connections making this scenario highly unlikely. Council will be encouraging infill development that is connected to these schemes. The only area of concern is the North Beach catchment as it currently relies on septic systems. The Council continues to progress connections to the CWMS throughout its jurisdiction.
Observed Condition
Expected Condition