Oysters are on the cutting edge of the restoration of our coastlines.
Oysters are one of the most imperilled ecosystems on Earth. They’ve suffered an 85% decline globally, but in some areas of Australia this has been up to 99%. The main reason for their decline in Australia has been overfishing, and one of the reasons they haven’t come back has been habitat destruction.
It has been estimated that the total loss of oyster reefs in the first century of colonisation in Australia would rival the extent of the Great Barrier Reef.
We obviously know how delicious they are to eat, so we farm them. But what hasn’t been understood is their value to our coastal ecosystems when they occur naturally, and build up into vast oyster reefs in our bays and estuaries. When the First Fleet explored the bays of Sydney Harbour, they noted some individual oyster reefs covering up to 10 hectares. This was not unusual. It has been estimated that the total loss of oyster reefs in the first century of colonisation in Australia would rival the extent of the Great Barrier Reef. Today, less than 1% of these historic reefs remain.
There is a big movement now to try and restore their numbers by recreating the oyster reefs that used to proliferate along our coasts and estuaries that have all but disappeared.
Read more: Indigenous people farmed oysters sustainably for 5000 years.
These oyster reefs are SO important for the health of our coastlines. Oysters play a role in water filtration, with a single oyster being able to filter almost 200L of water a day, and they also provide habitat for so many different species by creating amazing, complex, large reefs in the shallow coastal areas.
We also now know they reduce the height of waves when they approach the shores, acting like a living breakwater, protecting delicate shorelines from erosion.
We humans love to live on the coast for various reasons, but we create a lot of problems. I’m interested in not only looking at our impacts on this coastal environment, but researching solutions.
My research looks at how we can restore oyster reefs in areas that need protection against erosion, while giving biodiversity a real boost. If we can restore this lost habitat, we provide an opportunity for people to live on the coast in a much more sustainable way. The idea is that these oyster reefs provide this protection, while nurturing biodiversity, water filtration, and all the other amazing things that oyster reefs do.
There’s so much infrastructure on the coast, and all of this building has impacts on the natural ecosystems it replaces or fragments.
My research focuses on “ocean sprawl” of man-made structures. A lot of what we build actually enters the water for various reasons. When we build a bridge over an estuary there are pylons going straight into the water. We build sea walls and break waters to protect houses and harbours. We build infrastructure for boats, such as marinas and moorings. There’s so much infrastructure on the coast, and all of this building has impacts on the natural ecosystems it replaces or fragments. I want to find out how we can make this built infrastructure better habitats for species, and how we can harness nature so that we’ve got more of a natural living shoreline protected from erosion.
To create an oyster reef, you need thousands of individual oysters to cement themselves together to form these platforms. In their natural environment they build up in layers; as the bottom ones die they become a substrate for oysters to colonise on top, so you have a living layer of oysters sitting on a bed of rock or dead oyster shells, and this creates a really solid reef.
Read more: Southern recovery of ecosystem engineers.
Oysters need something hard to settle on to colonise, but we humans have removed of a lot of that hard substrate through fishing methods, like trawling, and dredging. We didn’t understand its importance.
Port Phillip Bay in Victoria is a good example. Through studies of the shell middens there, we know that First Nations people harvested oysters sustainably for at least 10,000 years. Then, within about 50 years after European colonisation, they were gone. Of course, it was extreme overfishing, but it was also the removal of these reefs on an industrial scale – the oyster shells on these reefs were dredged and then burned to produce the lime to manufacture cement to build our cities.
We know that some oysters will colonise on the infrastructure that humans have introduced. Oysters need to attach to something hard when they move from larvae in the water column to actually settling down, so one of the first things that you have to do is put down a hard substrate. This is one of the first steps in an oyster reef restoration project. You can then naturally recruit oysters, as we can do in areas of NSW, but in places like Port Phillip Bay where we have very, very low recruitment, you have to breed the oysters in the hatchery and then physically place them on these reefs.
The design of this substrate is vitally important, and determines whether you end up getting oysters or not. This is one of my main areas of research, working on designs for the best structures that will bring the oyster reefs back.
This is one of my main areas of research, working on designs for the best structures that will bring the oyster reefs back.
We start by trying everything from small scale, from the texture of the units that you install, up to what the actual shape the unit takes. We’ve recently been trying some novel technologies using 3D printing with industrial designer Reef Design Lab. We print 3D moulds that we can then cast in various materials to see which is most effective. We’re actually using models of natural oyster reefs to inform what our level of complexity should be.
Then we go right up to large scale, working out how we should place them to attenuate waves. For this we are working with scientists in Western Australia who have a wave flume, testing these units in the flume before positioning them out on the coast.
In Victoria I mainly work with the species Ostrea angasi, which is our native flat oyster. In NSW we generally work with the Sydney rock oyster, but there’s a few different species of oyster all the way from temperate to tropical Australia.
The next big thing will be the integration of these methods to create “living” shorelines and natural ecosystems where currently we have what we call “armoured” shorelines. We need to integrate these living shorelines into standard practice for coastal protection. Currently, it’s not. Currently, the default is this awful armoury – which will still have to be used in some areas, but not everywhere.
The next big thing will be the integration of these methods to create “living” shorelines and natural ecosystems where currently we have what we call “armoured” shorelines.
We know from public surveys that seeing natural shorelines is one of the reasons people love the coast. And yet we’re building big sea walls everywhere – these concreted shorelines. There has to be a better way.
The key thing for us is to show that these work. We need the data to back up the technical guidance. We need to demonstrate that everyone’s a winner with a more natural shoreline.
Originally published by Cosmos as Restoring oyster reefs to create “living” shorelines
Dr Becki Morris is a marine scientist at the University of Melbourne where she leads the Coastal and Estuarine Adaptation Lab, and is Theme Leader of Eco-engineering at the National Centre for Coasts and Climate. She is also a 2022 L’Oreal/UNESCO For Women In Science fellow, conducting research into how rebuilding oyster reefs impacts coastal erosion and promotes biodiversity.