Penrhyn Estuary Habitat Enhancement Plan: Results of Saltmarsh Monitoring

As part of the Port Botany Expansion Project, extensive modifications to Penrhyn Estuary including dune levelling have substantially altered intertidal saltmarsh habitat within the estuary. One of the objectives of the... [ view full abstract ]

As part of the Port Botany Expansion Project, extensive modifications to Penrhyn Estuary including dune levelling have substantially altered intertidal saltmarsh habitat within the estuary. One of the objectives of the rehabilitation works for the project was to expand the area of saltmarsh habitat within the estuary for roosting and foraging habitat for migratory shorebirds. The key objectives of the saltmarsh monitoring program were to assess the success of created saltmarsh habitat, including its ecological function. Monitoring was undertaken within a BACI framework that compared planted saltmarsh to natural saltmarsh habitat within Botany Bay as well as other constructed saltmarsh habitats.
Total area of saltmarsh habitat within the Penrhyn Estuary is estimated at over 40,000 m2, representing a 76% increase in habitat following enhancement works. Saltmarsh species diversity and abundance generally increased following the enhancement works and saltmarsh vegetation was generally in better condition compared to pre-enhancment. Importantly, the distribution and abundance of newly planted saltmarsh vegetation along the northern and southern shorelines continued to grow during the 2014 surveys, with Sporobolus virginicus increasing in all treatments, while Suaeda australis decreased slightly, consistent with selective removal. It appeared that areas that were recipients of transplanted saltmarsh did not increase in cover or diversity, although these areas appeared to maintain these vegetative indictors since baseline data was collected. Data indicate that epifaunal assemblages are recolonising areas that have been disturbed during the rehabilitation works and have recruited into newly planted areas of saltmarsh vegetation at levels comparable to reference habitats. A few mangrove seedlings were detected during monitoring, suggesting that mangrove management will be an ongoing requirement to prevent the re-establishment of mangrove habitat.
Overall, the majority of saltmarsh habitat investigated to date has responded favourably to the rehabilitation works following the expansion of the port, although a number of treatments have not responded as well as expected. These include areas that were transplanted with saltmarsh vegetation prior to enhancement works and areas that were cleared of mangroves and weeds. Notwithstanding this, both treatments generally maintained values similar to their baseline values and overall saltmarsh planting has been successful.