text: The trend in artificial reef development has been toward the construction of designed artificial reefs, built from materials specifically designed to function as reefs. Designed systems (such as reef balls) can be modified to achieve a variety of goals. These include coral reef rehabilitation, fishery enhancement, snorkeling and diving trails, beach erosion protection, surfing enhancement, fish spawning sites, planters for mangrove replanting, enhancement of lobster fisheries, creation of oyster reefs, estuary rehabilitation, and even exotic uses such as deep water Oculina coral replanting.  Designed systems can overcome many of the problems associated with "materials of opportunity" such as stability in storms, durability, biological fit, lack of potential pollution problems, availability, and reduction in long-term artificial reef costs.
  Designed reefs have been developed specifically for coral reef rehabilitation, and can therefore be used in a more specific niche than materials of opportunity. Some examples of specialized adaptations which "designed reefs" can use include: specialized surface textures, coral planting attachment points, specialized pH-neutral surfaces (such as neutralized concrete, ceramics, or mineral accretion surfaces), fissures to create currents for corals, and avoidance of materials such as iron (which may cause algae to overgrow coral).  Other types of designed systems can create aquaculture opportunities for lobsters, create oyster beds, or be used for a large variety of other specialized needs.