Reef structures and stabilisation

 

Repairing damaged reef surfaces

When reefs are damaged (for example by storms, ship groundings or coral bleaching) the dead or degraded coral can become loose and unconsolidated rubble, making it difficult for coral to regrow.

Mesh or netting is sometimes installed over the rubble to prevent further movement. Often, young corals are then transplanted onto the damaged area, or on artificial reef structures. This technique is relatively common in the US, funded by insurance claims following ship strikes; however, there is a lack of published information and research about this technique.

Stabilisation by removal: removing loose rubble from a damaged reef via a surface-operated suction device to aid reef recovery. This approach has been successfully applied on reefs affected by ship and boat strikes.

To date these methods have been limited to small, localised sites. New approaches would need to be developed for this to be applied at larger scales.

Other methods to be investigated by the RRAP Research and Development Program include:

Stabilisation by natural bonding: using natural bonding agents from organisms (including crustose coralline algae or biological adhesives) to help consolidate the reef surface to increase the rate of reef recovery.

Stabilisation by chemical bonding: using manufactured chemical bonding/grouting agents to help consolidate the reef surface to increase the rate of reef recovery following a disturbance. 

Stabilisation by consolidation: Consolidating rubble with gabion baskets to stabilise reef substrate and provide 3D structure to aid reef recovery. The mesh baskets would be filled with rubble, providing limited structure and habitat. They would be fabricated and filled onshore and deployed using large barges.

Novel human-made structures

Novel, human-made structures for coral settlement (new shapes, sizes and surfaces) can enhance reef structural complexity, and provide surfaces to promote coral resettlement and growth. They can range from micro-scale engineering to artificial reefs.

At local scales, artificial reefs have been constructed from a variety of materials to provide a suitable structure for coral settlement and reef function. They range in size from clusters of reef balls (1-3m diameter) to reef frameworks extending over hundreds of metres. Work is underway to test the effect of reef surface shape, aspect and other factors to maximise coral larval settlement and survival. This group of potential intervention methods also includes:

Structure by massive corals: Deploying, or in situ re-skinning, natural coral shapes. Artificial massive corals are concrete structures with a coral skin attached. The corals would be grown separately, attached to the structures, and deployed from barges and vessels.

Photo: Coral Spiders in Indonesia. Photographer: Jordan Hollarsmith, UC. Watch a short video for more information about this method