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THE WETLANDS
The area surrounding Jervis Bay is a perfect example
of the unique lifecycle of the wetlands environment. |
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THE GREY MANGROVE
The Grey Mangrove is the most widespread mangrove
in the world. It is the dominate mangrove on this walk,
growing as a medium sized tree with a well defined trunk
and numerous vertical peg roots (pneumatophores). The
leaves are green above and greyish below and occur opposite
one another on the stem. The fruit normally falls in
summer. The Grey Mangrove prefers to grow closer to
the seawater than the River Mangrove. |
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THE ESTUARY FOOD WEB
Mangroves, saltmarshes, mudflats and seagrass beds
form the basis of complex food webs. Together they support
a wealth of life from microbes through to fish and birds.
Mangrove leaves decompose to provide food for other
marine life. Solar energy plus nutrients in river sediments
provide the basic resources for mangroves to grow. Each
year more than 100 tonnes of mangrove leaves are produced
and fall into the estuaries of Jervis Bay. These break
down with the aid of microbes. This detritus is then
consumed by marine snails, crabs, fish and prawns. |
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SALTWATER & SURVIVAL
Mangroves are trees which are suited to a life in saltwater
by being able to get rid of the salt and obtain oxygen
for their roots. Salt secreting mangroves such as the
Grey and River Mangroves are able to concentrate and
exude the salt through special glands on their leaves.
The salt crystals which you can see on their leaves
are washed off during rain. The Grey Mangrove has developed
specialised air breathing roots (pneumatophores) which
grow out of the water-logged soil into the air. During
low tide they let enough air in to last the next tidal
cycle. The River Mangrove has a very shallow root system
that plays a similar role. |
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TREES BEARING LIVE YOUNG
After flowering, the two mangrove species in Jervis
Bay produce seed that grow on the parent tree for 10-12
months. Unlike most land plants the offspring are developed
and ready to grow when they fall from the tree. After
floating about in the saltwater for a few days the seedlings
strand and eventually stand themselves up. Many thousands
of seedlings establish themselves each year but most
die after a few years under the canopy of their parents.
If an old tree dies there are plenty of seedlings to
take its place. |
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COMMERCIAL IMPORTANCE
Mangrove habitats act as an important nursery for many
economically important fish species caught by both the
recreational angler and commercial fishermen.
Species include bream,blackfish, mullet, flathead, whiting
and red bream. It has been estimated that over 70% by
value of the commercial fish catch in New South Wales
is made up of estuarine-dependent fish. |
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FEEDING GROUNDS
Over 150 species of birds have been identified in or
around the wetlands of Jervis Bay,some of these are
migratory waders, such as godwits and sandpipers which
fly fromJapan and Siberia to the wetlands of southeastern
Australia each year.
The most common permanent species include White Ibis,
White Egret, Nankeen Night Heron, Grey Teal, Little
Pied Cormorant, Black Cormorant, White Breasted Sea
Eagle and White Face Heron. |
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LIFE IN THE MUD
The muddy surface beneath you abounds with life of
all shapes and sizes. The smallest are the bacteria
that form pink and white patches on the mud. Slightly
larger are the microscopic plants called micro-algae
that often form a green mat on the surface. The larger
visible brownalgae are the seaweed Neptunes Necklace
(Hormosira)One of the larger animals is the Fiddler
Crab (Grapsid) that lives in a network of burrows. If
the tide is out and you stand still you will see them
sifting the mud for food. Whelks also search themud
for microbes and detritus. These muddy ecosystems are
home to seven species of crabs and twenty species of
fish. |
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SEAGRASSES
Seagrasses are marine flowering plants. Three different
types are found in the waters of Jervis Bay. The broad
leaved strapweed (Posidonia) forms extensive beds in
the bay. The oval leaved paddleweed (Halophila) is also
common, but less conspicuous. The third is the narrow
leavedeelgrass (Zostera) found mainly in the creeks.
Seagrasses play a vital role in the marine environment
by providing shelter and feeding areas for a variety
of marine life such as crabs, prawns and shellfish. |
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ABORIGINAL HISTORY
For thousands of years Aboriginal groups occupied
the Jervis Bay area, harvesting many marine animals
as the major part of their food supply. Middens along
the shores of Currumbene Creek indicate that they collected
oysters, whelks, bream, flathead etc from the estuary.
The fish were speared with multi - pronged spears in
the shallows or from bark canoes, sometimes at night
with the aid of bark torches. |
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THE RIVER MANGROVE
The River Mangrove (Aegiceras corniculatum), found
throughout Australian and Asian mangrove ecosystems,
is generally a small shrub, often with several small
trunks, and no peg roots. The leaves are glossy green
above and paler under- neath and occur alternately along
the stem. The flowers are white and clustered together.
The fruit is small, curved and viviparous (germinates
on the tree), and normally falls in winter. The River
Mangrove usually occurs behind the Grey Mangroves near
the saltmarsh areas. |
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SALTMARSH
Saltmarshes occur between the mangroves and the high
tide level. The saltmarsh plants are covered by high
tides once or twice a month and become covered in salt
crystals as they dry. They are an important buffer between
the land and the estuary, providing habitats for marine
snails, crabs and birds. Jervis Bay saltmarshes provide
summer feeding grounds for migratory birds such as the
curlews, godwits and sandpipers. |
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