W
hen most people think of an oyster they think
of small clusters clinging to rocks here or there,
but once they formed vast solid reef structures
just like a coral reef in our bays.
The living reefs were made up of oysters, algae, sponges,
urchins and fish. More than 100 years ago, Port Phillip Bay
was filled with oyster reefs and mussel beds but, after many
years of commercial dredging, pollution, introduced species
and disease, the shellfish reefs have almost disappeared.
There are still mussels and oysters to be found in Corio
Bay and Port Phillip Bay, but they are no longer forming
reef structures.
Now The Nature Conservancy has teamed up with
Fisheries Victoria and the Albert Park Yachting & Angling
Club for a pilot project to bring shellfish reefs back to Port
Phillip Bay. Wilsons Spit Reef in the Geelong Arm is one
site benefitting from the project.
Marine manager Dr Chris Gillies, who is part of the team
undertaking Australia’s first project to re-establish shellfish
reefs, regularly works and dives down at Queenscliff.
“I oversee the Great Southern Seascapes program, which
is all about scaling up the amount of restoration that occurs
for marine habitats in bays and estuaries across southern
Australia,” Chris says.
“Our program is about how we undo some of the past
and begin to restore some of these habitats. It’s not just for
the value of nature. We also do it to increase the number
of fish, to increase water filtration and also to protect our
coastlines. Seagrass beds and shellfish reefs are really
good at acting as nursery grounds for producing fish. The
shellfish reefs also filter a lot of water, so they help clean
and clear the water.”
The project is working to restore shellfish reefs at Hobsons
Bay (Margaret’s Reef). Chris says shellfish reefs were once
REEFS ARE BEING BROUGHT BACK TO LIFE THANKS
TO A NEW PROJECT, WRITES JULIA MILLARD
“we dredged
out all of the
oysters, &
they haven’t
come back”
one of the most common habitats in bays and estuaries such
as Port Phillip Bay, right up to central Queensland, through
to Perth and down to Tasmania.
“The early explorers came along and saw a food resource
there that they were used to and they harvested them,”
he says.
“So there were big dredge fisheries in all the bays and
estuaries across southern Australia in the mid to late 1800s.
And by the early 1900s most of the fisheries had collapsed;
we dredged out all of the oysters and they haven’t come
back. So now we are giving them a helping hand.”
Chris says the oysters were dredged for two reasons. One
was to eat and the other was to burn the shell for lime to be
used in concrete and plaster.
“A lot of Melbourne and Geelong’s early buildings around
the 1850s to ’60s would more than likely have oysters used
as part of the construction materials,” he says.
Now it’s about putting oysters back into the bay – not for
eating but for habitat.
The project sources baby oysters from the Queenscliff
Shellfish Hatchery and, during the spawning stage, millions
of oyster larvae are released and settle on scallop shells. The
larvae are then left to grow into juvenile oysters for three to
(REG RYAN)
A SEA CHANGE
six months on commercial farming leases in the bay.
The team is trialling laying limestone rock onto the
sea floor to provide a foundation for the juvenile oysters to
settle on and grow into reefs.
The work has started with square metre plots, which
Chris is hoping will turn into hectares of reef. About 6000
native flat oysters and three tonnes of blue mussels have so
far been deployed.
“We are recreating habitat on a significant scale so it
starts to influence the surrounding area in terms of not only
being environmentally viable but also beginning to produce
fish,” Chris says.
“Because we have spent 100 years dredging, we have
moved a lot of the hard surfaces. There is a lot of sand
and mud, which is really mobile, so when the oysters and
mussels settle they get buried. We are putting limestone
down and we will eventually be putting shells down, as they
like to settle on those.”
A shellfish recycling program in the Geelong region is
next on the agenda. Chris says restaurants and businesses
can help by donating used shells to the project, which will
be cured (to eliminate disease) and then put back out in the
bay as a base for the reefs.
“We are also looking to start up an oyster gardening
program, where you can throw oysters off a jetty or pier and
it helps us to determine if they can survive there,” he says.
“Another one will be a settlement plate study, where we are
looking for those baby oysters in the system and where they
are settling or will settle.
“We’d like to see in 10 to 20 years’ time that there are
oyster reefs throughout this section and people are catching
fish from those reefs. Corio Bay was quite a hot spot for
oyster reefs.” ●
[email protected]
The Nature
Conservancy
project
For more information
or to donate, visit: www.
natureaustralia.org.au/
our-impact/water/
port-phillip-bay/
DR CHRIS GILLIES
DECEMBER 17, 2015 \ THE WEEKLY REVIEW 17