Once the fish factories and ‘kidneys’ of colder seas, Australia’s decimated shell reefs are returning

Australia once had vast reefs of oysters and mussels, which anchored marine ecosystems and provided an essential food source for coastal First Nations. But after colonization, Europeans harvested them for meat and shellfish and drove the oyster and mussel reefs to near extinction. Because the damage was done early – and much of it underwater – the destruction of these reefs has been all but forgotten.

Not anymore. We learned how to restore these vital reef systems. After a successful pilot project in 2015, 46 shell reef restorations are now underway – the largest marine restoration program ever undertaken in Australia. It’s not too soon. There is only one natural reef left for the endangered Australian Olympia oyster.

How did shellfish reefs go from oblivion to the front line? Our new research shows how this historic amnesia was overcome thanks to a nationwide community of researchers, conservationists, and government and fisheries managers.

This is important, because oysters and mussels are ecological superheroes. By restoring these reefs, we are giving local marine life a real boost and supporting human livelihoods that depend on healthy seas. These cold-water reefs play a role similar to coral in tropical seas. They provide hiding places and food for baby fish, filter seawater and defend coasts against wave erosion.

Large-scale shellfish reef restoration projects began with a single pilot project in 2015 and have grown to 46 projects nationwide by 2022.

What killed our original shell reefs?

Just 200 years ago, shell reefs carpeted the temperate regions of Australia, filling sheltered bays and estuaries along more than 7,000 kilometers of coastline.

Archaeological research in Queensland shows that First Nations peoples were sustainably harvesting local shell reefs for at least 5,000 years, replenishing oyster populations by building reefs with rocks and shells.

This ended when the Europeans took the lands and waters from the traditional owners. Shellfish became one of colonial Australia’s first fisheries. Oysters were fished extensively for food, while their shells were burned to make lime for fertilizer and cement. If you pass a colonial era building, look at the mortar. Chances are a lot of oyster shells went in there.

Read more: The world’s most degraded marine ecosystem could be about to make a comeback

Even though wild fishing ended a century ago, these shells have not been able to come back. This is because they cannot just grow on bare sand. Their favorite substrate is the shellfish of their ancestors, left on the sea floor. molds could settle in and grow.

Today there is only one small natural flat oyster reef (Ostrea angasi) and six remains of Sydney rock oysters (Saccostrea glomerata) remaining reefs, in all Australian waters.

Colonial oyster fishermen used oyster dredges, rakes, and shovels to scrape oysters from the seabed.
State Library of South Australia

How to Start Shellfish Reef Restoration

Seashells cannot recover on their own. But it turns out that with a little human help, they can. Think of it as compensation for our unsustainable use.

For a decade before the first large-scale restoration, recreational fishing groups and community groups worked on smaller projects, sometimes with government support.

To undertake restoration work on a larger scale, it was first necessary to remember how it once was. Because the ecological collapse of Australia’s shellfish reefs has been so profound, they have almost disappeared from human memory. Historical records have guided us on what a restored ecosystem should look like and where these reefs are.

Australia’s only native Olympia oyster (Ostrea angasi) reef is found in eastern Tasmania. Olympia oyster reefs have been dredged to oblivion for thousands of miles off Australia’s southern coast.

Our work has been made easier because of the tremendous benefits shell reefs provide to marine life. Intact oyster and mussel reefs are natural fish factories that provide nursery habitats for economically important fish species such as bream and whiting.

Read more: The surprising health benefits of oysters (and no, it’s not what you think)

Even better, these filter-feeding shells are the kidneys of the coast, cleaning up water that is cloudy with sediment or overloaded with nutrients. A single oyster can filter 100 liters of water per day. Shell reefs also act as living defenses against wave energy, store carbon in their shells, and help protect intertidal communities from global warming through shade and moisture at low tide.

People working on reef restoration have turned to our burgeoning oyster and mussel farming industry to understand their life cycles and what they need to thrive. The success of these farms indicates that many areas have remained suitable for shellfish reefs.

Environmental NGO The Nature Conservancy connected the emerging reef restoration community and brought hands-on experience from longer-running shell restoration projects to America. Reef restoration work is now led by conservation NGOs, local and state governments and, increasingly, community groups.

So it works ? Yes. It’s as if the oysters are waiting for this opportunity. Many artificial reefs have been colonized by millions of baby oysters within months of being built, such as the largest project to date, the 20-hectare Windara Reef in South Australia. Some restored reefs approach oyster densities in line with natural reefs.

Looking forward

We hope that the rapid upsurge in shellfish reef restoration heralds a new era for large-scale marine restoration in Australia.

Today, community restorations are growing and multiplying, and public support for shell restoration is widespread.

It’s an impressive story. This is a national recovery program that is showing significant successes with relatively modest investment. These restoration efforts show that large-scale action to fix nature can work — and work fast — when experts from diverse disciplines work with communities toward a common goal.

As restored oyster and mussel reefs mature, we will see more fish in our seas and more opportunities for recreation and tourism will emerge. This, in turn, could inspire more communities to restore their own shellfish reefs. Together we can revive the reefs that have lived in our colder seas for millennia.

Read more: Huge restored reef aims to bring South Australia’s oysters back from the brink

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