Artificial or man-made reefs are human made structures that mimic characteristics of natural reefs. They are intentionally deployed to enhance fisheries and tourism, but can also be used for surfing, diving, aquaculture and engineering solutions for coastal erosion. In Australia, artificial reefs are mainly deployed to increase the abundance and diversity of marine life by creating additional shelter, food sources and a surface for colonisation.
There are two types of artificial reefs, purpose-built artificial reefs and materials of opportunity. Materials of opportunity are pre-existing materials prior to designing the reef and can include concrete blocks and rubble, stones, pipe, tyres, ships, car bodies, oil rigs and disused army forces equipment which is deployed to form a reef. Though favoured in the past due to their cheap cost they have since become unfavourable in Australia. There decrease in popularity is due to past failures of such reefs such as incorrect design and deployment, adverse environmental effects and structures being dislodged by extreme weather and hydrological events.
Tyre reefs, were once a common artificial reef but have now stopped being deployed around the world due to the negative effects on marine life. One of the biggest examples of this is the Osborne Artificial Reef off the coast of Florida which deployed over two million tyres bound with steel clips over 150km2. The steel clips corroded resulting in the loss of two million light weight tyres. The unrestrained tyres then destroyed the small amount of marine growth on them and became easily subjected to storm and winds (hurricanes spread and washed up thousands of these tyres).
Materials of opportunity such as vehicles and ships can be suitable for deploying as an artificial reef, however they have to be rigorously cleaned with all pollutants such as paint removed. Even after this it still may not be approved by environmental organisations for deployment, so the cost and resources needed make this type of reef an unfeasible and environmentally irresponsible option.
Tyres, plastic pipe, cars, ships and vehicles can also have negative impacts on marine life through leaching zinc and other heavy metals, benzothiazoles and a range of hydrocarbons into the water. These pollutants are toxic to all forms of marine life causing a range of health effects on wildlife depending on the level of exposure and susceptibility. Furthermore there is a high cost to the community for the safe removal of such reefs.
Purpose-built artificial reefs are specifically designed for species, habitats or effects (such as upwelling) having preferred shapes, voids, surface and profiles. They are seen as the future as they have no negative environmental impacts and are cheaper in the long term, especially from the social, ecological and economic benefits of the reefs. A big benefit of purpose-built artificial reefs is shape, size and form can be altered to increase the abundance of certain species.
For example, the abalone reefs (Abitats) used by Ocean Grown Abalone off Augusta support the abalone throughout its growth and maximise the amount of abalone on that can be grown on each module. Similarly metal towers such as the Sydney Offshore Artificial Reef have been used to increase the numbers of pelagic species such as Yellowtail Kingfish by providing vertical profile through multiple levels in the water column.
The Mandurah purpose-built artificial reefs also increase habitat opportunities through changing environmental conditions in the water column. Each module is designed to promote upwelling by driving nutrient rich water up from the seafloor by the curved cross braces assisting the food chain. These modules also create shelter and habitat for smaller fish such as Wrasse, Bullseye, Yellowtail Scad and Footballer Sweep, which will then propagate larger species such as Dhufish, Pink Snapper and Samson Fish.
The modules also vary light, temperature and water movement as well as increasing 3-dimensional surfaces, all of which increases the habitat available for marine organisms.
Purpose-built artificial reefs are environmentally responsible and do not damage the marine environment in anyway. Australian Legislation requires monitoring plans to ensure reefs do not damage the environment and prior to deployment the reefs pass rigorous approvals process to ensure they provide the best outcome for fishers, fish and the marine environment.
For more on Artificial Reefs, including our Mandurah Reefs, South West Reefs and Perth Metro reefs, click here.