Oyster research aims to clean the water of Sydney Harbour

Between the bricks of some of Sydney’s oldest buildings are hidden clues about the city’s past. The mortar holding together buildings such as Vaucluse House and Hyde Park Barracks is studded with shell fragments – many from creatures that have all but disappeared from Sydney’s harbour and other estuaries.

In the early days of white settlement, the harbour was full of oyster reefs, so large, ships had to navigate around them. The colonists harvested them – along with shells they found in Aboriginal middens – and used them to make the mortar that built the city.

Today, most of Sydney’s oyster reefs have been wiped out by fishing and industry. The area is still home to a smaller number of Sydney rock oysters and the invasive Pacific oysters originally from Japanese waters, but a once-common variety of native flat oyster – Ostrea angasi – has vanished.

Now, the oyster reefs are set to make a comeback, thanks to researchers at the Sydney Institute of Marine Science (SIMS).

Over the next five years, a SIMS team led by the University of Sydney will work to restore the reefs around the city, and perhaps even bring back the lost angasi species. The project, a collaboration between the University of Sydney, the University of New South Wales, Macquarie University and University of Technology Sydney, could have long-term benefits for the harbour’s health.

Oysters, says Associate Professor Paul Gribben, director of the Sydney Harbour Research Program, are “the kidneys of the water”, filtering out excess nutrients and heavy metals. For this reason, it’s not a good idea to eat harbour oysters, but in restoring the reefs, the scientists hope to not only improve water quality, but also create hotspots for biodiversity.

Oyster reefs provide a habitat for all creatures: snails, crabs and other invertebrates, which in turn attract fish.

The reefs can even help buffer the shoreline from wave damage – a growing concern thanks to the predicted consequences of climate change.

Working out where to place the new reefs will require careful thought and preparation, with the first step being a thorough assessment of Sydney’s remnant natural reefs.

That’s what brings a small group of marine scientists to the boat ramp at Port Botany on a bright, cold day in June. It seems an unlikely spot to begin a quest for one of the city’s last remaining natural reefs. Planes roar as they take off from the airport nearby. Cranes loom above warehouses clustered along the shore.

But as the researchers’ tinny pulls away from land, the industrial landscape recedes and the water is unusually clear. At the tiller is Associate Professor Ross Coleman, from the University of Sydney’s Centre for Research on Ecological Impacts of Coastal Cities. Also aboard are marine biologists Dr Ana Bugnot (PhD(Research) ’14) from the University of Sydney and Dr Katherine Dafforn from Macquarie University.

From a distance, the reefs look like long, flat slabs of brown rock just breaking through the water. Draw closer and their surfaces are crusty with the shells of thousands of creatures. While oysters on sea walls or breakwaters grow in a single layer, natural reefs like this one can build up many layers of oysters, clinging to nothing but each other.

Over the next few hours, the scientists will wade through the water to collect sediment samples and make observations. They hope to use this reef as a control, comparing it to the new ones they will create.

“We want to check out the habitats around the reefs,” says Dr Bugnot. “We’re also interested in their size and how healthy they look, and whether there are any oyster predators on the spot.”

All of this will inform the rest of the project. The locations of the new reefs are yet to be determined, but the focus will be on estuaries in the Sydney area, such as the harbour and Botany Bay – well away from paddlers and swimmers.

Once the researchers have selected the sites, they will plant structures made of concrete. The hope – backed by existing research – is that oysters already in the water will settle on the concrete, kickstarting the growth of natural reefs.

Oysters prefer company, so the scientists may plant some living specimens to help the new reefs grow. This is how they plan to bring back the lost angasi species.

Angasis were particularly popular with the early settlers. They closely resembled the flat oysters of the northern hemisphere and were easy to harvest. Where other species in Australia prefer to attach to rocky surfaces, angasis could be found loose in silty or sandy-bottomed estuaries. The Europeans harvested them almost to extinction.

“We’d like to put angasi back into Sydney Harbour, where angasi should be,” says Associate Professor Coleman.

The long-term plan is to seed reefs with angasis bred in laboratories or fisheries. The process will be carefully managed within the quarantine rules that govern the movement of oysters between habitats.

Oyster farmers elsewhere in Australia are already experimenting with angasis – the variety’s strong flavour is making it increasingly popular with foodies. The native oysters are seen by some as a potential solution to recent disease outbreaks that have decimated the more traditional varieties.

Despite these intriguing culinary possibilities, the research project is aiming only to create a recipe for rehabilitation. The scientists hope to develop guidelines for restoring oyster reefs that could be used in similar environments elsewhere.

For now, prepare for the Sydney Harbour water view to include re-established oyster reefs.

Support marine research

The oyster restoration project is possible thanks to a generous donation from the Maple-Brown Family Foundation. You can support this research or find out more by phoning +61 2 8627 8818 or emailing development.fund@sydney.edu.au

Written by Louise Schwartzkoff (BA(Media&Comm) ’07)
Photography by Stefanie Zingsheim