On the map, zoom in and click on the dots to view underwater video at each site.
Seagrass habitats were dominated by moderate to dense meadows of Posidonia spp.
Rocky reef habitats were comprised of dense canopies of large brown algae with diverse communities of red and green fine branching algae filling out the understory
Area map
About the Biounit
The Nuyts Biounit is located in the Murat bioregion and is seaward from the Streaky biounit. The biounit is generally offshore in deep waters and parts experience high wave energy. The waters within the biounit that were between 2-15m deep compromised mainly of offshore islands of the Nuyts archipelago, which includes the St Francis and Franklin groups of Islands.
The subtidal granite outcrops are dominated by large brown and red algal communities. In the lee of islands (typically to the north east) seagrasses can thrive and are dominated by Posidonia spp., and Amphibolis spp.
The Nuyts Archipelago Marine Park is the largest marine park in South Australia and aims to protecting examples of the unique diversity of sea life arising due to the warm water currents arriving through the Leeuwin current from tropical Western Australia.
The offshore nature of the biounit results in very few threats to the nearshore habitats around each island. Occasional visitation from fishing and sailing vessels and climate change are the only likely human impacts in the nearshore waters.
The Archipelago however, is a Birdlife International Internationally important bird and biodiversity area (IBA). St Francis Island in particular is home to approximately 1% of the global population of short tailed shearwaters, white faced storm petrels and pied oystercatchers. The island has historically been used for guano mining.
The assessment of identified threats to the nearshore habitats predicts that the Nuyts biounit is likely to be in Excellent condition.
In summary
Sites sampled were a mix of habitats including moderate to dense Posidonia spp. in all areas sheltered by the islands. The seagrass had sporadic epiphyte loads through the meadows near Franklin Island, however moderate to dense epiphyte loads were observed around St. Francis Island. The epiphytes at tehse locations appeared to be morphologically different to the filamentous algae, which are typical of nutrient enriched areas. This highlights that more work on epiphyte composition in relation to “natural” versus nutrient enriched environments is required.
Low profile reef observed close to Franklin Island supported dense communities of Eckloniaradiata and diverse communities of red algae.
Findings
The condition of habitats in waters between 2–15 m deep throughout the Nuyts biounit was assessed based on monitoring data collected during autumn and spring 2014. Areas within the biounit that are deeper than 15 m are not included as a part of this assessment.
The isolation and exposure of this biounit resulted in 2 sites assessed in autumn and spring as well as 3 sites around St. Francis Island in spring only. The waters were relatively high energy, even in the sheltered bays around St. Francis Island and Franklin Islands.
Franklin Island south (m0435) consisted of moderate to dense meadows of Posidonia spp. This seagrass was interspersed with low profile reef, dominated by Ecklonia radiata and diverse communities of red algae. The seagrass epiphyte load at this site appeared to be consistent with the red algal communities on the rocky substrate, which may be unrelated to nutrient enrichment.
Sites in Petrel Bay in the lee of St Francis Island were monitored in spring only with all sites consisting of dense Posidonia spp. seagrass with moderate to dense epiphyte loads recorded at all sites. The epiphytes were filamentous brown macroalgae (Cladisiphon filum and Polycerea nigrescens) and appeared visually different to those common in nutrient enriched locations. This may be related to the offshore location, the nature of the nutrient source or a natural seagrass epiphyte composition based on adjacent macroalgal communities. Their presence may also be related to the high densities of birds that inhabit the islands.
This assessment suggests that Nuyts was in Excellent condition. This typically indicates that the structure and function of the habitats are considered to be in natural or unimpacted condition and the waters are oligotrophic.
The findings presented here are explained more thoroughly in the Eyre & Murat Assessment Report.
Pressures and management responses
Pressures
Management responses
High densities of birds inhabit St Francis Island and the Nuyts archipelago. The islands are home to an estimated 1% of the global population of the short tailed shearwater (Puffinus tenuirostris), white faced storm petrel (Pelagodroma marina) and the pied oystercatcher (Haematopus longirostris)
Birds are a natural part of the ecosystem and the Nuyts archipelago has been named as an Important Bird and Biodiversity Area (IBA) by Birdlife International.
The subtidal environment at St Francis Island are likely to be resilient to this nutrient source as shown by the Excellent grade.