Streaky Nearshore Marine Biounit
2019 Aquatic Ecosystem Condition Report

The Streaky Biounit extends along a stretch of coastline that encompasses many small bays including the townships of Streaky Bay, Smoky Bay and Ceduna. The bays are relatively shallow and are connected to the wider ocean through deeper, narrow channels. A number of sites close to towns are in Poor condition and have degraded further since 2014, while sites that are further away from townships or are fully flushed more regularly by tidal currents are in Good or Very Good condition.

Sites that have degraded further since 2014 appears to be driven by nutrient enrichment, supported by numerous indicators such as the seagrass loss, phytoplankton communities, bioturbation, dense epiphytes and opportunistic algae. Many of the inner bays are poorly flushed, meaning any nutrient inputs are retained where they can degrade habitats.

The score classifies sites on the ecological condition based on habitat integrity outlined in the methods report. This score does not reflect suitability of the sites for other purposes including aquaculture production.

The condition of habitats in waters between 2–15 m deep throughout the Streaky biounit was assessed based on monitoring data collected during autumn 2019. The score classifies sites on the ecological condition based on habitat integrity outlined in the methods report. This score does not reflect suitability of the sites for other purposes including aquaculture production.

Site	2019
	Condition	Trend
m0427, Blanche Port	Good
m0428, Point Gibson	Good
m0429, Pigface Is.	Poor
m0432, Inside Dashwood Rock	Fair
m0433, Warburton Channel	Very Poor
m0434, West of Pt. Lindsay	Very Good
m0437, Cape Missiessy	Very Good
m0438, Smoky Bay	Fair
m0440, Eyre Is.	Good
m0442, Laura Bay	Good
m0443, St Peter Island	Very Good
m0447, Ceduna	Very good
m0448, Murat Bay North	Fair

The sites closest to Streaky Bay township: Blanche Port (m0427), Point Gibson (m0428) and Pigface Is. (m0429) all show signs of nutrient enrichment with high epiphyte and opportunistic algae. 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 (Hincksia sordida) which is often indicators of nutrient enrichment. This was outlined in the 2015 AECR and since that time, Pigface Island has declined in seagrass cover from 63% down to 17%, and Port Gibson has declined from 65% down to 50% indicating substantial changes in condition. These sites have been observed in both surveys to have heavy epiphyte loads and opportunistic algae and elevated Fp ratio all point towards problems with prolonged excess nutrients. It is likely that without urgent action to assess and control nutrient input, further habitat decline is likely. At some sites sedimentation is evident on seagrass leaves, and is likely due to changing landscape uses close to townships and is an additional pressure.

The sites closest to Smoky Bay (m0438) has reduced seagrass cover since 2014 with seagrass cover declining from 85% down to 43%. The site West of Pt Lindsay (m0434) remains in very good condition, Cape Missiessy (m0437) and Laura Bay (m0442) have a small increase in seagrass cover.

Of the 3 sites closest to the town of Ceduna, St Peter Is. (m0443) and Ceduna (m0447) show dense seagrass meadows in Very Good condition, but the site, Murat Bay North (m0448) has declined in condition from 2014 with less seagrass cover and high epiphyte load.

The more exposed parts of the biounit were often dominated by rocky reef habitat typically comprised of large brown canopy alga Ecklonia radiata 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 decline in condition as a result of dense epiphyte growth and opportunistic algae at the sheltered sites suggests that parts of the biounit are degrading due to nutrient enrichment. At a number of sites, there was seagrass persisting despite the epiphyte load, it is possible that these sites are very shallow and habitats are still gaining sufficient light to persist, however the deeper margins of the meadows at likely to be at risk. This suggests that some of the condition scores could be considered conservative.

• Download the Methods Report for the nearshore marine ecosystems monitoring, evaluation and reporting program.

These pages outline the statistical analysis undertaken for the Streaky Biounit. It should be read in conjunction with the AECR for that biounit. The methods used for the collection of the information are detailed in marine methods.

The habitat variables; total seagrass cover, bare sand, epiphyte and opportunistic algae were used to compare sites over the years they were monitored using Primer v7 with the PERMANOVA add-on^[1]. The data was square root transformed and all transects in a site were analysed for each year of monitoring. Principal coordinate ordination (PCO), with variables overlain as vectors was used to explore the data for groups.

The multivariate PERMANOVA test showed there are differences in the composition of sites and this can be seen in the separation of the sites within the PCO (Figure 1). This demonstrates that the sites that are considered quite dissimilar to others, particularly m0432 and m0433, are located well to the right of the plot. These sites were typified by reef habitats or bare sand and were typically devoid of seagrass. The remaining sites were clustered, but difference in location show some differences in habitat composition between years (Figure 1). Pairwise comparisons were performed to discern which sites were different between years (Table 2). In order to provide conservative results, a p value of 0.01 was used to indicate significant differences.

Figure 1   Principal coordinate ordination with vectors of habitat variables overlaid for 2014 and 2019 habitat data.

Apart from sites Inside Dashwood Rock (m0432), Cape Missiessy (m0437) and Laura Bay (m0442), all other sites showed a significant difference between years. The differences varied across sites and were due to declines in seagrass cover, increase in epiphyte and/or opportunistic algae. All of these findings can be linked to decline in condition using the disturbance gradients outlined in the Methods document^[2].

The Fp ratios and the phytoplankton size categories also indicate nutrient enrichment at a number of sites (m0427, m0428, m0429) close to Streaky Bay, suggesting that regardless of the benthic vegetation, the system had excess nutrients. There is a general trend that sites that are in the shallowest and poorly flushed areas where townships have developed, show the greatest declines in condition and highest Fp ratios consistent with excess nutrients.

The site m0433 showed elevated Fp ratio (Figure 3) and a dominance of large phytoplankton cells (Figure 4), this site also showed a decline in seagrass cover to now be almost bare indicating a shift form a vegetated community to one dominated by phytoplankton, a typical progression through a eutrophication model^[3]. This site is located in a reasonable well flushed part of the bay which may increase the hydrodynamic stress on seagrass if impacted by nutrients.

Table 1  PERMANOVA on sqrt transformed 2014 and 2019 habitat data (total SG, bare sand, epiphyte and opportunistic algae). P values of less than 0.01 were considered significant.

Table 2    Pairwise comparisons on sqrt transformed 2014 and 2019 habitat data for all sites in Fowlers after generating resemblances using Bray-Curtis similarities. P values of less than 0.01 were considered significant.

Figure 2   Benthic habitat composition at each site in Streaky Biounit for all years monitored.

Figure 3   Fp ratios for each site in Streaky biounits in 2019. Oligotrophic conditions are considered to have an Fp ratio less than 0.3, mesotrophic conditions are above 0.3 and less than 0.7, and eutrophic conditions are signified by an Fp ratio above 0.7.

Figure 4   Size classes for phytoplankton communities in Streaky Biounit in 2019

While the AECR score is developed from a set of metrics outlined in the Methods document. This document outlines the key information used and additional statistical analysis undertaken to interpret the results of the AECR for these sites. It provides the confidence that the AECR score is consistent with the scientific interpretation and attempts to understand the pressures acting on the system.

This document does not outline all data collected for this program, additional data (eg: water chemistry) can be downloaded on the download data tab on the website or by contacting the EPA.

[1] Anderson, M., Gorley, R. and Clarke, R. (2008) Permanova+ for Primer: Guide to Software and Statistical Methods. Plymouth, UK.: Primer-E Ltd.

[2] Gaylard, S., Nelson, M. and Noble, W., Authority, E.P. (2013) The South Australian monitoring, reporting and evaluation program for aquatic ecosystems: Rationale and methods for the assessment of nearshore marine waters. Environment Protection Authority Adelaide. 79 pp.

[3] Cloern, J. E. (2001) 'Our evolving conceptual model of the coastal eutrophication problem', Marine Ecology Progress Series, 210(2001), pp. 223–253.