Oyster reef restoration – recruitment

Want some more detail about what I’ve been up to lately?

Juan (left) and myself (right) recording water quality data.

We’ve been setting up an experiment to understand what environmental factors prevent or encourage the recruitment of baby oysters (commonly referred to as “spat”). This will then help inform future restoration efforts as we try and restore natural oyster reefs to their former glory.

In temperate systems, oyster reefs act like coral reefs do in tropical systems. They form large reefs in soft sediments that create a hard, complex structure that supports a whole ecosystem. We’ve lost more than 80% of natural oyster reefs in New South Wales, Australia since colonisation. These reefs are vital for biodiversity and provide habitat for a large number of invertebrates (crustaceans, worms, snails, etc.) and fish. As fish habitat, they provide a refuge and a food source at high tide for many species, including recreationally and commercially important species.

A natural oyster reef! This one is in the Bermagui River on the far south coast of NSW.

There’s no doubt our estuaries (coastal rivers and lakes) have suffered from the decline of oyster reefs. That’s where this current work comes in! Our team at Macquarie University, along with teams at The University of NSW, The University of Sydney and NSW DPI Fisheries are working to restore natural oysters reefs.

A natural oyster reef in the Bermagui River with associated seaweed and seagrass!

The project I’m currently working on is for Master student Juan, who’s thesis is on understanding the limitations to natural oyster reefs growing and reforming. We’re deploying concrete blocks in a number of NSW estuaries at different sites up the river, which will help us understand the influence of freshwater. At these sites, blocks are at three depths to inform us on where future restoration should take place (exposed at low tide? always submerged? or somewhere in between?) Half of the blocks are also caged, which will tell us the whether fish eating the baby oysters limits their survival!

One of our sites in the Shoalhaven River, showing the mid intertidal and low intertidal concrete blocks, half of which have cages to keep the fish out!

The team deploying the experiment at sunrise! No better time to be on the water.

In half of the estuaries, we are also deploying stacks of a starch-based, biodegradable mesh that is used to restore natural habitats and then biodegrade over time! The idea is to put these units in at the same depths as the concrete blocks to test which depth is best to get maximum recruitment of baby oysters. Then, over time, more oysters will setlle on the units and the previous years oysters, forming a natural reef as the mesh units biodegrade, leaving just the oysters!