Download9 Other Human Uses and Impacts

Artificial Reefs

Environmental impacts from artificial reefs should remain localised provided the relevant OSPAR guidelines are followed.

There are around 50 artificial reefs in the OSPAR area. These are located at various sites within Regions I to IV. There are no artificial reefs in Region V. Most have been created in the past two decades and are purpose-built and made of concrete. Their purpose ranges from improving marine resources, compensating for, and protecting against, habitat loss, to providing recreational dive sites. Effects on the general biodiversity are unclear and opinions differ as to whether artificial reefs increase the productivity of fish species or whether they serve to concentrate them. Localised impacts on the marine environment are possible, for example, changes to waves and currents and displacement and changes to biological communities. Monitoring confirms that environmental impacts around artificial reefs are local and of limited intensity.

Box 9.6 Sancti Petri artificial reef in the Gulf of Cadiz (Spain)

The Sancti Petri artificial reef is situated off the coast of Cadiz at a depth of between 15 and 40 m (see map). The area attracts a high level of artisanal fishing activity. In 2000, the Spanish Ministry of Agriculture, Fisheries and Food started to develop a reef to protect fish populations from the action of illegal bottom trawlers, thereby reducing catch pressure, avoiding damage to artisanal fishing gear and reducing social conflicts. The reef was completed in 2005.

The reef complex comprises three reef zones, each with three barrier structures placed perpendicular to the favoured trawling routes. The barriers are separated by one nautical mile of free area. The barriers are rectangular structures between 2 and 4 km long and 200 m wide, comprising modular units (see photo).

Each artificial reef unit is a 5.5 tonne reinforced concrete cylinder with a 3 m foot to prevent it from sinking into the seabed. Units are typically placed 75 to 200 m apart to form the barriers. A total of 569 units have been placed creating 2845 m2 of reef within an overall protected area of 4818 ha.

The performance of the reef is monitored in several ways. Every two years, a structural and functional survey is carried out using side scan sonar. In addition, the artisanal fishing catches are regulated and the fishermen are consulted using opinion polls. The results show a dramatic decrease in illegal trawling activity in the area and an increase in artisanal catch.

The limited spatial extent and inherent physical and chemical stability of the reef mean that no significant impacts have been detected. Entanglement of trammel nets occurs occasionally, but does not appear to result in ‘ghost fishing’.

The design, choice of material and placement of artificial reefs in the OSPAR area are mostly subject to national authorisation, supported by EIAs. OSPAR has developed guidelines for artificial reefs that are specifically built for protecting, regenerating, concentrating and/or increasing the production of living marine resources. These recognise that negative impacts are possible at the local scale. The United Nations Environment Programme (UNEP) and the London Convention have prepared guidelines covering artificial reefs built for a wider range of purposes.

Because most of the impacts from artificial reefs are relatively local, as long as there is not a massive increase in the number of reefs and the OSPAR, UNEP and London Convention guidelines are followed, the development of artificial reefs is not expected to have major negative effects in the OSPAR area. However, monitoring the extent of this activity will assist further consideration of its impacts. To facilitate this, OSPAR should establish an inventory of artificial reefs.