NEW SOUTH WALES Wet Summer to Winter Transition
The New South Wales (NSW) coast is a high wave-energy coastline, where mangroves are confined within sheltered embayments and estuaries. Of the 133 estuaries and small coastal creeks in the state, 69 contain mangroves, covering a combined area of 107 km2. Floristic diversity declines with increasing latitude, from six species near the NSW/Queensland border, to two in the Sydney region. Aegiceras corniculatum occurs further south to Merimbula Lake after which only scattered individuals of Avicennia marina are found in the Wonboyn River near the Victorian border. Other species are confined to the northern estuaries of NSW, with the southernmost occurrence of Rhizophora stylosa at South West Rocks Creek (30º 53’ S, 153º 02’ E). Rhizophora stylosa and Bruguiera gymnorhiza are most common in the back-barrier north and south arms associated with these river systems. Palynological evidence from the Richmond River suggests these species were previously more extensive. Their presence in the region had declined over the past 6000 years. This comes in contrast to very recent observations of expansion of Avicennia marina into neighbouring saltmarsh habitat in many NSW estuaries. The reason for this recent proliferation appears to be related to human influences including climate change.
High biomass forests
Mangroves forests can attain considerable biomass. In the Hawkesbury River (330 34’ S, 1510 20’ E), where new mudflats contain elevated nutrient levels, Avicennia marina grow to 16 m. Mangrove height increases with distance upstream as plants take advantage of lower salinities.
State of Transition
The north-south coastline has a gradient of decreasing mangrove diversity that contrasts with increasing saltmarsh diversity. Mangrove species range from six in the north to one, Avicennia marina, near the NSW/Victorian border. Mangroves co-exist between saltmarsh and seagrass, and together they contribute towards fisheries and food chains of estuaries.
High Human Population Numbers
Coastal areas have high populations especially along the central coast from Wollongong to Newcastle. Mangroves have been a casualty of the ‘seachange’ shift bringing further residential and industrial development to coastal areas. Levels of loss are, however, being contained with greater community awareness and better statutory protection.
- Acrostichum speciosum - NR
- Aegiceras corniculatum - NR,CN,SN
- Avicennia marina var. australasica - NR,CN,SN
- Bruguiera gymnorhiza - NR
- Excoecaria agallocha var. agallocha - NR,CN
- Rhizophora stylosa - NR
- Aegiceras corniculatum
- photo: Chris Harty
Mangrove cover has increased dramatically in many NSW estuaries, by up to 50% in some estuaries. Much of this proliferation has been at the expense of high conservation value saltmarsh, and migratory shorebird roosting habitat.
Mangroves occur naturally along the whole New South Wales coast, including the Jervis Bay Territory, within tidal estuaries, coastal lakes and embayments (Ozestuaries 2006), largely influenced by wet summers, micro tides and moderate waves. Three regions are based on the types of mangrove habitat determined by varying geological and physiographic settings.
Northern Rivers (NR) - Broad River Estuaries and Coastal Creeks
Tweed Heads to the Hastings River at Port Macquarie – 32 estuaries in 7 local catchment areas. The geomorphology of this region is dominated by Holocene and Pleistocene barriers, dissected by large coastal rivers and numerous creeks. Contains the highest diversity of mangroves, notably in back-barrier depressions connected to main river channels. Climate is subtropical, with a distinct summer rainfall peak. Frosts are rare to absent. This region has 6 species of mangroves.
South Coast (SN) - Coastal Lakes and Lagoons
Shoalhaven River at Nowra, to Nadgee Lake and Cape Howe – 21 estuaries in 6 local catchment areas. Includes the Jervis Bay Territory. Sandstone bedrock coastlines with few large rivers and numerous barrier estuaries. Aegiceras corniculatum is rare, extending as far south as Merimbula Lake. Mangroves may be absent from intermittently closed/open lakes and lagoons. Frosts may be frequent, though not intense. This region has 2 species of mangroves.
Central Coast and Sydney (CN) - Drowned River Valleys
Manning River at Taree, to the Woolongong Coast – 16 estuaries in 7 local catchment areas. The region is characterised by sandstone bedrock coastlines with numerous drowned river valleys, including the Hawkesbury River, Port Jackson, Botany Bay/Georges River and Port Hacking around Sydney. Mangrove communities consisting of Avicennia marina and Aegiceras corniculatum dominate these estuaries with the latter species often forming dense thickets upstream. This region has 3 species of mangroves.
South East (SE) - Subtropical Transition and Large Sand Islands
Curtis Island to Currumbin Creek on the Gold Coast - 16 local catchment areas, span humid subtropical areas with meso tides. Brisbane River in Moreton Bay includes 6 species, although just two dominate, namely Avicennia marina generally, and Aegiceras corniculatum in upstream reaches. The region has 14 mangroves, with a total mangrove area of ~533 km2.
A light gap in mangroves of Homebush Bay shows the continuing process of natural gap formation. Such gaps are believed to be caused by lightning strikes.Mangroves are affected by a range of natural processes. Erosion undercuts mangrove trees and shrubs resulting in their loss, and deposition of sediments buries breathing roots resulting in suffocation of trees. Insects attack and defoliate trees that may die, especially if stressed further by other factors. Over the past half-century, regional climate and sea-level change has promoted colonisation of saltmarsh by mangrove. Mangroves have increased in extent by a median rate up to 50% in some estuaries. In some instances, this increase has been at the expense of high conservation value coastal saltmarsh habitat. This habitat is reportedly important as migratory shorebird roosting habitat, although this is arguable. As mangroves attempt to migrate landward with sea level rise, they are also threatened by ‘coastal squeeze’ when blocked by coastal structures such as sea walls and embankments. Increased rainfall levels combined with increased temperatures with climate change may have produced conditions favourable for mangrove proliferation over the last few decades.
Mangroves will be squeezed between rising sea levels and associated tide and coastal structures like this sea wall in Merimbula Lake south coast of NSW. Photo: Chris HartyIncreased population size and development along the coast has focussed chiefly on the central coast around Sydney. This has led to some notable human impacts including:- proliferation of mangroves with increased estuarine sedimentation caused by the clearing of catchments; direct destruction of mangroves from reclamation projects for residential (eg. canal estates), industrial and sporting developments (eg. Cronulla Rugby League club facility); clearing and trampling of mangroves for seeking waterway views and access with jetties for fishing and access; polluted runoff comprised of nutrients, chemicals and highly turbid stormwater associated with urban and agricultural land uses; and, the blocking or restriction of tidal exchange and flows with causeways, embankments or sea wall structures have led to the loss of mangroves and their replacement with marginal weed species.
Community conservation & education
Public appreciation of mangroves has increased as indicated by the popularity of boardwalks now established in many estuarine environments. Boardwalks with informative signage occur in places like Tweed Heads in the Ukerabagh Nature Reserve, the Lady Denman Maritime Museum at Huskisson in Jervis Bay, and Cullendulla Creek near Batemans Bay. General public access is available at most mangrove areas either by land or boat, however, such access can be inappropriate with damage caused to mangrove roots from vehicles and frequent trampling. Community interest in mangroves has seen planting projects for erosion control by community groups like the Shoalhaven Riverwatch Inc. along the Shoalhaven River. Education about the value and threats to mangroves are supported by facilities like the ‘Welcome Walk’ on Kooragang Island near Newcastle and the local Wetlands Centre. Research on mangroves has focussed on mapping the extent of mangrove area and historic change using aerial photography. Having an abundance of mangrove study sites within close proximity to cities like Sydney and Newcastle encourages student research. A number of local councils have prepared estuary management plans, which also have included mangroves as part of their assessment of values, threats and management of estuarine vegetation habitats.
Mangroves have been cleared since European colonisation and used for various products, including soap manufacture, and supporting structures for oyster farming. As the importance of mangroves to fish became appreciated in the 20th century, they were protected under legislation and planning policies, including the following:- Fisheries Management Act 1994 under a permit system for damaging marine vegetation including mangroves, making it illegal to remove mangroves in New South Wales without a permit from NSW Fisheries; Fish Habitat Protection Plan No. 1 – General, 1995 prepared under the Fisheries Management Act 1994; State Environmental Planning Policy No. 14 - Coastal Wetlands (SEPP14); State Environmental Planning Policy No. 71 – Coastal Protection (SEPP71); General protection under various Regional and Local Environmental Plans such as the Sydney Regional Environmental Plan (Sydney Harbour Catchment) 2005 developed under the provisions of the Environmental Planning and Assessment Act 1979; a policy under the NSW Coastal Policy 1997; and, listing under the Ramsar Convention including mangroves located within the Hunter River Estuary Ramsar site in Newcastle.