Recycling an old bridge and dead coral to restore reefs

In an attempt to restore bleaching coral reefs, initiatives make artificial reefs using an old bridge and dead coral.

Coral reefs are diverse underwater ecosystems, often dubbed as the rainforests of the sea. When coral reefs are stressed by changes in conditions, such as temperature, light or nutrients, they expel the symbiotic algae living in their tissues, turning them completely white, an effect known as bleaching. Read more about this problem here.

Artificial reefs are built to promote marine life. Algae, barnacles, corals and oysters attach to the hard surfaces, providing an intricate structure and food for assemblages of fish.

Recycled bridge
The old Tappan Zee Bridge in New York will be reused as an artificial reef. The bridge stopped being used last year, when a new bridge, known as the Governor Mario M. Cuomo Bridge, opened across the Hudson River.

The Tappan Zee Bridge was in use for 62 years, but closed due a number of reasons, including high accident rates and maintenance costs.

The bridge will be cleaned of toxic chemicals and approved by the State Department of Environmental Conservation for reuse. The concrete and clean, recycled materials from the demolition will be used to create five reefs off the South Shore and one in the Long Island Sound. The reefs will also include sinking old barges and tug boats to help create the reefs.

Dead coral
A collaborative project involving the University of Queensland in Australia aims to restore the Great Barrier Reef, the world’s largest coral reef, by recycling broken and dead coral. The initiative investigates how creating a coral-filled net structures to turn unstable rubble into coral structures known as ‘bommies’.

The idea is to take broken coral from the sea bed, wrap it in a net made of natural fibres to provide a stable base for new coral to grow and place these bommies in such a way to protect other areas of the reef from cyclone wave damage.

When a reef is healthy, the wave energy is reduced by the coral structure, enabling broken coral to naturally bind to form a stable layer, initially through the growth of crustose coralline algae. This helps to bind the rubble together to create a framework for reefs and releases chemical that attract free-swimming coral larvae. By stabilising and compressing the broken rubble into a single stable mound, this process should be assisted.

The team hopes to show that strategically placing the 2m-diameter bommies will fast-track the repair of damaged areas and provide enhanced fish habitats while protecting existing exposed corals from further damage.

Photos: Acropora /  Nrbelex / Pxhere