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How structures made from oyster shells can help prevent coastal erosion

Reef Design Lab based in Melbourne uses locally sourced oyster shells mixed with concrete to build structures that reduce coastal erosion and support marine wildlife.

Along the shore of Port Phillip Bay in Australia, large dome-shaped modules sit submerged just below the water’s surface.

Though they resemble large sand dollars at first, these structures have been man-made by the Reef Design Lab in Melbourne. They were constructed using a blend of concrete and ground-up oyster shells, with the aim of reducing erosion occurring along Australia’s coast.

Many places around the world are witnessing an increase in coastal erosion. The consequences are wide-ranging, including the loss of homes and businesses, as well as damage to infrastructure and agricultural production.

When coastal erosion increases the amount of sediment in oceans, it can pollute rivers and other streams, causing disruption to natural marine life and vital water reserves.

Though significant episodes of coastal erosion are typically associated with extreme weather events, the process is also driven over time by strong waves and currents, as well as mass wasting processes on slopes and land subsidence.

Thanks to the team at Reef Design Lab, a sustainable and eco-friendly mitigation strategy is seeing success along Australia’s coastlines. Let’s take a look at their creative process.

Named Erosion Mitigation Units, the domes are two metres wide and form a barrier around 60 metres offshore.

This organic shape helps to maintain their structural integrity, minimise material use, and create habitable colonies for ocean life.

To create the domes, the team in Melbourne used digital moulding analysis alongside traditional casting techniques. This allowed for the development of a reusable precast mould that uses less concrete than 3D printing techniques.

When it came to building the structures, Reef Design Lab added crushed-up locally sourced oyster shells with concrete before pouring it into the moulds. The unique shape and geometric patterns of the modules were chosen to create favourable conditions needed for marine species to live on them.

A slight overhang provides a spot for stingrays and pufferfish,  Inside the tunnels and caves of the module, octopus, smaller fish, and crustaceans are able to hide from larger predators. These inlets also offer shade for sponges and cold water coral to latch onto.

The surface of each module was intentionally left rough to the touch in hopes of being able to attract reef-building species such as worms and shellfish, in particular, mussels and oysters.

As they needed to be placed in shallower waters to complete their job as breakwaters, the modules were designed to retain water in order to shelter intertidal species during low tide periods.

Reef Design Lab installed 46 of its domes beneath the shallow waters of Port Phillip Bay last October. Over the next five years, they will be monitored by the Melbourne Universities Centre for Coasts and Climate to see whether they complete their job while attracting sea life.

Only six months after the modules were installed, numerous species of shellfish, sponges, and cold-water corals have been seen living in and around them. This is great news, as it means the structural design and surface texture are successful.

As storms increase in strength and frequency due to our planet’s changing climate, natural and eco-friendly solutions like the domes made at Reef Design Lab will be welcomed by those living in other coastal areas of Australia.

With a design that is proven to work, it wouldn’t be surprising if we saw them popping up all over the world.