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Artificial Reefs and their replacement

By goGreen | November 2, 2011
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People are destroying coral reefs and other important fish habitats at an unprecedented rate. Destructive fishing practices and pollution are the two main causes. While many NGOs are very actively trying to convince the worlds politicians to take action to prevent harmful practices, practical actions are also being undertaken by many local communities.

As coral reefs are destroyed the communities living in the coastal area suffer first from depletion of fish stocks. The shorelines, where their houses and businesses are and where boats are moored, also suffer, as they are no longer protected from the sea by the reef. Once a community has felt the effects of the loss of the reef, they may decide to take action.

One part of a solution could be for the community to build artificial reefs. It takes many, many years for the coral that makes up the structure of a reef to grow. Artificial reefs (ARs) have a long tradition in many parts of the world. In recent years, however, the use of modern materials has greatly increased their potential. For example the use of purpose-built building blocks called modules, constructed from cement, plastics, and steel, has enabled the construction of relatively large structures using simple techniques (see examples below).

One part of a solution could be for the community to build artificial reefs. It takes many, many years for the coral that makes up the structure of a reef to grow. Artificial reefs (ARs) have a long tradition in many parts of the world. In recent years, however, the use of modern materials has greatly increased their potential. For example the use of purpose-built building blocks called modules, constructed from cement, plastics, and steel, has enabled the construction of relatively large structures using simple techniques (see examples below).

Their use has advantages and disadvantages. They can be very valuable in repairing damaged reefs and re-establishing reefs that have been destroyed, but only if the reefs are to be used as nurseries or sanctuaries, or if they are to be fished using traditional methods. If entirely new reefs are being created in areas that are already over-fished, they may exacerbate the problem by drawing fish to the new reef, where they are more easily caught. Reefs should also be built with materials that will not contaminate the area if they are disturbed or break down.

For the artificial reefs to contribute to sustainable fisheries in the longer term, it is important that the fishing communities are involved in all steps of the decision-making and development processes. They should participate in the selection of the reefs sites, the choice of materials, the management and monitoring of the reefs, and in their evaluation. It must be the community’s decision to proceed (or not) at each stage of the process.

After the community has agreed to go ahead, there are two main phases to creating the artificial reef: construction, and placement.

Construction Variety

It is important when constructing the reef to provide as much diversity of habitat as possible, as this encourages the greatest diversity of species. The greater the biodiversity living on the reef, the healthier the reef will be. Use m any different types of modules, including well rings, ferrocement modules, tyres, granite boulders, coconut stumps, poles, pipes, bottles, and whatever else is available locally. Use them in a variety of combinations and orientations.

Clusters

It is important to cluster plenty of material together densely; the more the better. Very dispersed materials will not be colonized successfully, and will only be wasted. (See later for a suggested technique for placement.)

Orientation of the clusters is also important. Line structures or clusters should be placed so that they are across the current. This provides a sheltered environment for smaller fishes, and a standing wave above the reef, which throws up food for a variety of species. Before you begin placing the reef material set two marker buoys in the water and a land transit to give you an approximate line to follow.

Crevices

Ensure that the reef that you are creating has plenty of holes and crevices to provide refuge and shelter from predators and current. The greater the variety of size, density, and orientation of the crevices the better, as they will shelter a wider variety of creatures. Crevices can be created in a number of ways, usually by leaving holes in fabricated modules or attaching materials such as broken pipes to the modules to create holes. Whole or broken pantiles, bottles, cooking pots, buckets, flower pots, and bricks are just some of the many items that can be glued onto modules to create interesting crevices. It is also important to attach natural or synthetic fibres to the reef modules. They make a very attractive substrate for the smallest of creatures, and are ideal places for cuttlefish to lay their eggs.

Height

It is recommended that reefs should be about one-third of the water depth. If that is not possible, then you should at least introduce a number of taller modules into the reef. Height makes it easier for roving predatory fish to locate the reef, thereby increasing further the biodiversity of the reef. The reef will act like a beacon, and in times of sediment disturbances the highest objects may still show above the sediment cloud or projected dies and disturbances further afield.

Height can be achieved in a number of ways, for example by using salvaged telegraph posts or pipes, or poles made from concrete, wood, or galvanized iron. You could also make Ferro cement fins, or bamboo or wooden tripods. If none of those materials are available you can create height cheaply using air too. Floats or plastic containers full of air or other buoyant items can be tied with rope to modules. Other small items can be tied along the length of the rope to provide crevices and surfaces on which biomass can begin to accumulate and grow.

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