Yanerbie Nearshore Marine Biounit
2019 Aquatic Ecosystem Condition Report

Habitats within Venus Bay showed a transition related to distance from the mouth of the Bay that may be broadly associated with the residence time of water. Posidonia australis was found to be prevalent around Port Kenny (m0421) with a gradual transition towards Heterozostera spp. mixed with intermittent fine branching green algae in the middle of the Bay shifting to a mix of fine branching green algae and Heterozostera sp. becoming sparse at west Venus Bay (m0425).

There were some indicators of nutrient enrichment during autumn, including seagrass epiphytes, which were prevalent on the Posidonia australis seagrass. 

The isolation and exposure of Yanerbie resulted in 4 sites being assessed. All of these sites were located within Venus Bay. Caution has been applied when interpreting the condition assessment from Venus Bay due to the unique nature of the bay.

Site	2019
	Condition	Trend
m0421, Port Kenny	Fair
m0422, Venus Bay Is.	Fair
m0423, Venus Bay	Poor
m0425, West Venus Bay	Poor

Habitats within Venus Bay were a mix of different species, but there was a transition in composition which was likely related to distance from the mouth. Posidonia australis was prevalent around Port Kenny (m0421) with a gradual transition towards Heterozostera spp. mixed with intermittent fine branching green algae in the middle of the Bay. This shifted to fine branching green algae dominant with Heterozostera sp. becoming sparse. This transition was supported by the Fp ratio, which indicates increasing nutrient enrichment with distance from the mouth of Venus Bay.

This assessment of condition indicates a decline in half of the sites in Yanerbie, suggesting that the habitats that receive regular flushing of fresh oceanic water close to the mouth of Venus Bay are largely intact, but less flushed sites where excess nutrients can accumulate are showing signs of decline.

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

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

The habitat variables; total seagrass cover, bare sand, epiphyte, opportunistic algae and fine branching green 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.

Figure 1   PCO with vectors overlaid between sites and years for 2014 and 2019 habitat data.

Habitats within Venus Bay were a mix of different species, but there was a transition in composition which was likely related to distance from the mouth. Posidonia australis was prevalent around Port Kenny (m0421) with a gradual transition towards Heterozostera spp. mixed with intermittent fine branching green algae in the middle of the Bay. This shifted to fine branching green algae dominant with Heterozostera sp. becoming sparse. Visually, m0425 and m0423 can be seen to change considerably through their distance between their points between years on the PCO (Figure 1). This was supported by the habitat graphs indicating a loss of seagrass at these sites (Figure 2). The transition of habitats and of condition, was further supported by the Fp ratio and the size class information (Figures 3 and 4), indicating increasing nutrient enrichment with distance from the mouth of Venus Bay.

PERMANOVA showed there are differences in the composition of sites across the bay (Table 1). Pairwise comparisons were performed to discern which sites were different between years (Table 2). All sites showed significant difference over the years monitored. The differences varied across sites and were due to declines in seagrass cover, increase in epiphyte and/or opportunistic algae and increased cover of fine green algae.

All of these findings, except increase in fine branching green algae can be linked to decline in condition using the disturbance gradients outlined in the Methods document^[2]. There is evidence to suggest that in nutrient enriched environments there can be increases in abundances of algae^[3][4]. In each of the sites that demonstrated an increase in fine green algae or seagrass decline, additional indicators of nutrient enrichment were observed including Fp ratios indicative of eutrophic environments (Figure 2) and size classes of phytoplankton indicating a dominance of large celled organisms (Figure 3), suggesting that regardless of the benthic vegetation, the system had excess nutrients. For this reason we have cautiously applied this change as negative, which is also supported by findings at other sites within the system.

Table 1  PERMANOVA was performed 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 for each site was performed using fixed effects on sqrt transformed 2014 and 2019 habitat data for all sites in Yanerbie after generating resemblances using Bray–Curtis similarities. In order to be conservative p values of less than 0.01 were considered significant.

Figure 2   Benthic habitat composition at each site in Yanerbie biounit for all years monitored.

Figure 3   Fp ratios for each site in Yanerbie 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 class categories of phytoplankton communities in Yanerbie 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. (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] Kinney, E. H., & Roman, C. T. (1998). 'Response of primary producers to nutrient enrichment in a shallow estuary'. Marine Ecology Progress Series, 163, 89–98.

^[4] Lavery, P. S., Lukatelich, R. J., & McComb, A. J. (1991). 'Changes in the biomass and species composition of macroalgae in a eutrophic estuary'. Estuarine, Coastal and Shelf Science, 33(1), 1–22.