Shark Bay und seine Eigenheiten
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In Shark Bay's hot, dry climate, evaporation rates
are very high.
This causes the waters in its shallow bays to become
concentrated with salt.
Seagrass banks play a very important role in
maintaining high salt concentrations by restricting
tidal flows into and out of Shark Bay. This ensures
the open ocean does not dilute Shark Bay's salt-concentrated
Different parts of Shark Bay have different salt
concentrations, Shark Bay's waters are saltiest in
Hamelin Pool and Lharidon Bight.
Water in these areas is hypersaline, or twice as salty
as normal seawater.
The waters below Eagle Bluff are metahaline, meaning
they are up to 1.5 times as salty as the open ocean.
Most marine life cannot survive in hypersaline
waters, so there are few predators or competitors
in Hamelin Pool and Lharidon Bight.
Because of this, salt-tolerant life-forms, such as
the cyanobacteria which build stromatolites, and the
heart cockles which make-up Shell Beach, can flourish
in great numbers.
The marine life living in Shark Bay's metahaline
waters have also had to adapt to high salt concentrations.
Some of these animals, including Pink Snapper and clams,
are genetically very different from their cousins outside
of Shark Bay, and are growing more dissimilar as time
Shark Bay has three populations (stocks) of Pink
One consists of wide-ranging oceanic snapper, found
in waters north of the peninsulas, and along much of
the west coast.
The other two snapper populations are salt-adapted,
and live exclusively in Shark Bay's salty inner gulfs,
one in the eastern gulf, the other in the western gulf.
These populations do not interbreed, and are genetically
different from one another.
Given a few more thousand years, Shark Bay's salt-adapted
marine life may actually evolve into new species.
In fact some species, including the Shark Bay seasnake
and the jellyfish that lives among the stromatolites
in Hamelin Pool, already have!
Seagrasses are different from seaweed.
Seaweeds are marine algae that have no roots
Seagrasses have evolved from land plants that
have adapted to life underwater.
They have roots and produce underwater flowers.
Pollination occurs as ocean currents carry pollen from
flower to flower.
After the ice age, rising seas began to flood
into Shark Bay (about 7'000 years ago).
As the water rose, seagrasses started to grow in the
Bay's expanding shallow waters.
Seagrasses can only grow in shallow waters because
like most plants, they need lots of light for photosynthesis.
Because seagrass banks provide food and a sheltered
environment, they attract a wide abundance of marine
Seagrass banks slowly grow in height and size as they
accumulate the shells and skeletons of dead marine
These accumulations of shells, corals and skeletons
are called carbonate sediments.
Ironically, seagrasses' amazing ability to accumulate
sediment it also their downfall.
Eventually the seagrass banks grow too high, and the
seagrasses die, unable to survive exposure to the air
and sun during low tides, leaving a bare sandy or shelly
Today, Shark Bay is home to the largest seagrass
banks in the world, occupying some 400'000 ha (about
the size of the entire Perth metropolitan area).
These are the largest seagrass banks in the world,
and still growing.
No liability for timeliness, integrity and correctness of this document is accepted.
Friday, 17.02.2012 1:37 PM