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Sponge Gardens
About
Sponges
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As most divers will know, Victoria has some spectacular
sponge gardens. Sponges, hydroids and anemones, sea pens, sea whips,
tube-building worms, bryozoans, barnacles, ascidians and soft corals
are the major groups of animals in sponge garden communities. These
habitats flourish in shaded or deeper water as they are not dependent
on sunlight as algae and seagrasses are. Not only do sponge gardens
provide important habitat for other animals (and make a nice photo)
they are an important part of nutrient cycles in the marine systems
- filtering out particles and nutrients from the water as they feed. |
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Healthy
Sponge Habitats
Like all temperate life forms in Victorian waters the habitat forming
invertebrates in sponge gardens rely on clean water and sufficient nutrients
and food particles to survive. Because many of the animals are permanently
attached to the rock and unable to move around, they cannot go in search
of food or flee from harm. Sponge gardens are made up of delicate creatures
and many are very slow to grow - some living for decades. These factors
make sponge gardens susceptible to physically damaging processes such
as storms and human activities such as trawling and dredging.
Fishing, spearing and collecting are major human impacts on sponge garden
communities. Removal of key species such abalone, rock lobster, and wrasses
can upset the balance in these communities by allowing populations of
prey or food items to proliferate. Some fish species that aggregate in
sponge gardens are territorial or stay within a defined home range, for
example wrasses and morwongs, making them easy targets for spearing, netting
and trapping. No-fishing marine protected areas have been found to benefit
such species. For example, banded morwong inside New Zealand marine protected
areas are larger than fish in surrounding areas, and abundance and average
size of wrasses has also been shown to increase in areas free of fishing.
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Spongy
Bits
- Sponge gardens are factories of natural chemicals that have
recently created a great deal of excitement amongst scientists.
In order to prevent other organisms landing on them and growing
over them, sessile (i.e. permanently attached) animals such as
sponges and ascidians produce toxic chemicals or slime that inhibit
the settlement of other animals or bacteria. These chemicals may
have practical applications, for example as antibiotics or preventing
a build up of growth on the hulls of boats.
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- Sponges show an incredible variety of shapes: blobs, soft carpets,
long fingers, cones and cylinders. Not only is there variation
between species, but individuals of the same species grow differently
depending on environmental conditions. Sometimes an examination
under a microscope, or microchemistry, is the only way to correctly
identify them.
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- Sponge garden animals are generally sessile (i.e. permanently
attached) but many produce free-floating larvae that utilise currents
to spread to new areas. Most of these larvae are tiny and not
visible to the naked eye and may spend several minutes to a few
days floating in the water before settling into new areas.
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- Sessile animals from southern Australia are more diverse than
in other temperate regions of the world. Many species are found
only in this region including over half of the 500 sponges, 200
ascidians and 500 bryozoans.
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- Sponge garden animals may be either solitary or colonial and
made up of modules. For example, red throat sea squirts grow as
single animals while soft corals may be made up of hundreds of
individual polyps. While both forms are able to reproduce sexually,
colonial creatures have the added benefit of being able to grow
asexually - by cloning individual modules.
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Where Can You See Sponge Gardens?
Sponge Gardens can be found growing on all sorts of hard surfaces including
reefs and jetties.
West Coast: Shaded and deep areas of the Arches off Port Campbell,
Roger's Rocks, Killarney, Griffith Island, Lady Bay.
Central Coast: Flinders Pier Portsea
Pier, Lonsdale Wall and Nepean Wall at Port Phillip Heads, Portsea Hole.
East Coast: Beware Reef off Cape Conran.
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