CWM coast and marine icon

Coast and Marine

The city has approximately 31 kilometres of unique and varied coastline featuring open beaches, reefs, dunes and cliff formations. It is a diverse area that comprises a rich array of social, economic and environmental resources.

Our reefs provide important habitats for marine life and are popular recreation areas that attract visitors to the region. The challenge is to balance these competing demands and identify factors impacting our coastal resources. Sustainable management of the coast will allow our communities to enjoy coastal recreation activities while protecting both terrestrial and marine flora and fauna.
 

Indicator: Condition of reefs in the city
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Data source: Conservation Council of South Australia
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Strategies / Plans: Environment Strategy 2014-19
Coast and Natural Resources Strategic Management Plan (under development)
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Community Plan 2035: Objective 4.1 Valued Natural Resources
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Condition of reefs in the city

Reef Watch SA is an award-winning citizen science program in which volunteers work with marine scientists to gather valuable information about the health of South Australia’s marine environment. Since 2009, the Reef Watch program has undertaken seasonal surveys of six coastal reefs in the Adelaide and Mount Lofty Rangers (AMLR) Natural Resources Management Region to monitor and determine reef status or ‘health’. Two of the six coastal reefs monitored are located within the City of Onkaparinga–Noarlunga North Inside and Noarlunga South Inside.

The conditions of the reef system within the AMLR Natural Resources Management coast has been observed as having higher levels of degradation in reefs that are in Adelaide’s metropolitan coasts (ie Broken Bottom reef and Hallett Cove) compared with those located further south, including Second Valley and The Bluff (4).

Reef Watch observations are based on biological data from four reef community strata, including reef composition (reef cover), fish communities (abundance and species type), invertebrate predator community and the presence of invasive species. Within the four community reef strata, there are eight specific indices used to measure reef health. These eight indices specifically measure the percentage of cover of (i) canopy-forming macroalgae, (ii) base substrate, (iii) mussels mats (iv) turfing macroalgae, (v) the size and abundance of blue-throated wrasse, (vi) abundance of site-attached fish, (vii) the number of mobile invertebrate predators and (viii) the presence of invasive species.

The most recent data available for analysis was for the financial year 2014-15.
 

Data Analysis

In 2014-15, both the Noarlunga North Inside reef and the Noarlunga South Inside reef were assessed in each season (winter, autumn, summer and spring). Individual index scores (between 0 and 100) were then averaged to give an overall result for each site-season combination which was then interpreted according to a predetermined scale relating each reef to a status of either ‘poor’ (score between 0–34), ‘caution’ (score between 35–65) or ‘good’ (score between 66–100) (5). Scores were also averaged across seasons within each Noarlunga reef to allow comparisons between years (Figure 1).

As shown in Table 1, both the Noarlunga North Inside and Noarlunga South Inside reefs demonstrated health variability across seasons. The reason for the changes observed at the Noarlunga North Inside was due to a reduced level of canopy cover in the caution-rated seasons (5). The average annual score for the Noarlunga North Inside reef was 70 and the Noarlunga South Inside average annual score was lower at 42 (Figure 1).

Considering that there is a general observation that the reefs in Metropolitan Adelaide are degrading more than the reefs located further southwards, the consistently lower status of the Noarlunga South Inside reef, compared with the more northern Noarlunga North Inside reef, may be due to localised factors responsible for the observed reef decline (4). Therefore, further investigation may be required to determine what particular factors may be responsible for its health decline.

 

Table 1: Reef status and overall score for the Noarlunga North Inside reef and Noarlunga South Inside reef, 2014-15.

Site Season Status Overall score
Noarlunga North Inside Winter Caution 56
Spring Caution 58
Summer Good 86
Autumn Good 80
Noarlunga South Inside Winter Poor 28
Spring Caution 50
Summer Caution 50
Autumn Caution 40

Source: Westphalen, G (5)

The ‘caution-poor’ status of the Noarlunga South Inside reef in 2014-15 was due to low canopy cover, coupled with mussel cover. The most probable reason for the poor winter status, compared with all the other seasons, was the low presence of site-attached fish in winter (5).

Figure 1: Average reef status score across seasons, Noarlunga North Inside and Noarlunga South Inside, 2009-10 to 2014-15.

CWM-Coast-and-Marine-Average-reef-status-score-across-seasons
Source: Westphalen, G (5)

Trend Analysis

CWM coast and marine trend analysis

When comparing the condition of the Noarlunga South Inside reef over time, the status appears to be firmly sitting within the ‘caution’ band, in comparison, the Noarlunga Inside North reef status sits mostly within the ‘good’ or upper level of ‘caution’ (Figure 1). The average annual score for the Noarlunga North Inside reef in 2014-15 has improved by more than 29 per cent when compared with the 2009-10 score. Similarly, the average annual score for the Noarlunga South Inside has improved between 2009-10 and 2014-15 by more than 44 per cent.
 

Policy Implications

As outlined in the Environment Strategy 2014-19, the City of Onkaparinga will continue to protect our coastal amenity, manage coastal access and importantly advocate for protection of our coastal reefs and marine environment. Moreover, key initiatives including stormwater and wastewater reuse and the improvement in service levels of our stormwater infrastructure, as part of Water Proofing the South, will continue to support efforts to improve the condition of our reefs, particularly by reducing pollutant loads entering the marine environment. These strategies and initiatives will continue to contribute to achieving the Community Plan objective 4.1 Valued Natural Resources.

 

This indicator is linked to other strategies, plans and targets outlined below:

Government of South Australia South Australia’s Strategic Plan Targets: 71. Marine biodiversity: maintain the health and diversity of South Australia’s unique marine environments.
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Other State Strategies • Adelaide Coastal Water Quality Improvement Plan
• Adelaide's Living Beaches: A Strategy for 2005-2025
 Metropolitan Adelaide and Northern Coastal Action Plan 2009
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National Strategies: • Australia's Biodiversity Conservation Strategy 2010-2030
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