Sea pens within Bathurst Narrows
Marine
invertebrates
More than 500 species of
marine invertebrates (animals
without backbones) have been
recorded, with many still to
be described. Some, such as
anemones and zoanthids, bear
more resemblance to flowers
than animals. Most do not move,
anchoring themselves firmly to
the seafloor or channel walls,
where they feed on other
marine animals, or filter-feed
plankton and nutrients from the
swiftly flowing passing current.
There are single animals, like
sea urchins and seastars, and
colonial animals, which look
like one animal, but are in fact
hundreds of tiny animals living
together. There is safety and
efficiency in living as a colony.
Each animal within a colony has
a particular function – some
gather food, some strengthen
the colony and others even
clean the colony!
Many of the marine
invertebrates found in Bathurst
Channel are usually found
in much deeper and often
inaccessible ocean waters.
White-spotted dogfish
(Photo by Graham Edgar)
Fish, sharks, rays and eels
In outer Port Davey an unusual mix of fish species occurs. This is due to the incredibly exposed reefs and some influence from the tannins draining from the Davey River and Bathurst Channel. Fish species usually found around the Tasmanian coast, such as leatherjackets and barber perch, are absent. Instead, some species that do occur here are uncommon elsewhere.
In Bathurst Harbour and Bathurst Channel, the dark, poorly oxygenated, low nutrient waters attract few fish – with the most common being eels, sharks and skates. One species of cusk eel is unique to Port Davey. The endangered Maugean skate (also known as the Port Davey skate) occurs only in Bathurst Harbour and Macquarie Harbour. Both the Maugean skate and an unusual relative of the ice fish that also occurs here are related to species found in the fjords of New Zealand and South America – land masses to which Tasmania was once connected. Another species is the white-spotted dogfish, a species common in the region but listed on the IUCN Red List as threatened because of its globally declining population.
Of the three basic forms of seaweed
(brown, green and red), red seaweeds
are able to survive with the least sunlight,
at the deepest levels.
(Photo by Graham Edgar)
Seaweeds and
seagrasses
In the clearer marine waters
of outer Port Davey, the
typical variety of brown,
green and red seaweeds
thrive to depths of 10 m or
more. However in the darker
waters of Bathurst Harbour
and Bathurst Channel, where
tannins block out light,
marine plants are restricted
to the top few metres.
In quiet bays and coves,
seagrasses form underwater
meadows, providing shelter
for breeding fish and
invertebrates, and feeding
areas for black swans and
other waterbirds.
The Landscape
Many people mistake
the Port Davey
landscape, with its
steep-sided valleys and
convoluted shoreline,
for a glacial fjord. It is
in fact a drowned valley
or ria. At its centre is
Bathurst Harbour, which
was once a large plain
that flooded as the sea
level rose about 7000
years ago with late
melting of the last
ice age.
The harbour has since been
gathering a deepening layer
of ooze, some from the
surrounding plains, but mostly
from tiny sea animals, like
bryozoans. Bathurst Channel,
connecting Bathurst Harbour
with Port Davey, is a drowned
river. Swiftly flowing tidal
currents continually sweep the
channel floor, exposing resistant
rock.
As you walk across this
magnificent landscape, you’ll
often notice crunchy white
gravels underfoot. These began
as sand and mud laid down in
shallow seas up to a billion years
ago – long before Tasmania
looked anything remotely like it
does today. Over time, the sand
and mud was gradually buried,
metamorphosed by heat and
pressure into quartzites and
schists, then uplifted, folded and
partially eroded away. Younger
rocks (only half a billion years
old!) called conglomerates are
made up of pebbly fragments of
those earlier quartzites.
As well as the thin white lines
of walking tracks, quartzites and
conglomerates appear as snowlike
patches on the surrounding
mountains and white cliffs along
parts of the shoreline.
The soils that blanket much
of south-west Tasmania are
organosols. Loosely referred
to as peat, the thin organosols
form from undecomposed plant
material that slowly accumulates
under extremely wet, humid
and cool conditions.
The organosols support the
buttongrass moorland and
heathlands, which are so
typical of the south-west. The
moorlands have developed over
thousands of years, assisted by
regular burning by the Aboriginal
people.
The shores around the marine
reserve are often lined with
tea-tree, banksia and eucalypts.
In more sheltered areas where
mud slowly accumulates,
marshes and marsupial lawns
occur – the latter evolved from
constant grazing. In the steeper,
darker, wetter gullies of the many
rivers draining into the estuary,
a variety of wet forest species
grow, such as dogwood, myrtle,
sassafras and Huon pine.
Wildlife in the landscape
surrounding the marine reserve
includes wombats, wallabies,
a variety of small nocturnal
marsupials, burrowing crayfish,
and a delightful and colourful
chorus of daytime birds, insects
and frogs.