22 Jun 2020
Today, Sydney Olympic Park supports almost 100 hectares of estuarine wetlands, including the largest remaining stands of mangrove forest (73 ha) and Coastal Saltmarsh (25 ha) in the estuary! These habitats support a wide range of animals from the tiny crabs and fish to the incredible migratory Bar-tailed Godwits.
Mangrove forests and Coastal Saltmarsh naturally exist side by side within the tidal zone; mangroves between low tide and average high tide and Coastal Saltmarsh beyond the average high tide mark and extending towards the king tide limit. Historically, the Park’s estuarine wetlands have been highly modified by the construction of seawalls and bunds, consequently altering the natural ‘neighbourly’ balance of these ecological communities.
It’s a balancing act for the Authority as these historical alterations have allowed mangrove colonisation at the expense of Coastal Saltmarsh. As mangrove forests are classified as protected marine vegetation under NSW Fisheries Management Act 1994 and Coastal Saltmarsh is listed as an endangered ecological community under NSW Biodiversity Conservation Act 2016, finding the right balance is paramount.
Elevation and degree of saltwater inundation, combined with vegetation condition, provides the basis for identifying the line between mangrove and saltmarsh conservation.
To keep the balance, mangrove control activities are conducted under a permit issued by the Department of Primary Industries – Fisheries. Mangrove seedlings are removed from designated Coastal Saltmarsh and mudflat areas for conservation purposes on an annual basis, typically prior to reaching a height of 50cm. Removal is performed under strict conditions that minimise soil disturbance, wildlife disturbance and trampling of vegetation.
Protecting Coastal Saltmarsh and mudflat areas from mangrove colonisation benefits the wildlife that depends on this habitat. For example, internationally protected migratory shorebirds utilise saltmarsh and mudflat areas at the Waterbird Refuge and Newington Nature Reserve wetland as roosting and feeding habitat during their non-breeding season. These habitats are critical for migratory shorebird survival as the birds need to increase their body weight by up to 70% to build sufficient energy reserves to return to their breeding grounds in the northern hemisphere.
Recent works, conducted by bush regeneration contractors Total Earth Care, saw the removal of between 1200-2000 mangrove seedlings encroaching on saltmarsh and mudflat habitat at the Waterbird Refuge. Through ongoing strategic removal of mangroves and adaptive management of tidal regimes, the Authority will continue to strike a balance between these protected ecological communities to maintain biodiversity at the Park.
‘A line drawn in the mud’ – the tide regime naturally separates mangrove, mudflat and Coastal Saltmarsh habitats.
When the balance is thrown off, mangroves seedlings can invade Coastal Saltmarsh habitat.
The Authority manages a delicate balance between habitats, removing mangrove seedlings under a permit to preserve mudflat and Coastal Saltmarsh for dependent wildlife.