Reef Design & Types

The Right Stuff

OAR gets a lot of questions about what materials make a good reef? There is not an easy answer; there are a lot of variables, but we know we all want it to be done right and follow the principle of “do no harm” for all parties, both for marine life and people.

Good artificial reef materials share a few essential characteristics: They need to be stable, long-term, complex, and of course non-polluting.

Stable

Reefs that are lightweight or built of corrosive or brittle material will not stay in place during storms. Reefs should be stable for many reasons. If they are not stable, they cannot last in the long-term as described below. If they move with the currents and sea swells it will reduce their ability to create a long-lasting habitat. Reefs also need to stay within the boundaries of the permitted area, which are planned and designed to avoid natural hardbottom areas and, of course, navigational conflicts. Anglers are not too pleased to visit reef coordinates provided to them and then find no reefs or fish.

Long-term

A reef habitat is not created overnight. Studies have shown that reefs in Florida usually take about 3 to 5 years to become “MATURE.” Mature in this case is defined as the age of the reef when the fish population of the reef is equivalent to the surrounding, local natural reefs, which is the overarching goal of new reef structures. A reef that is too light to stay in place and falls apart, will fail to meet this criterion.

Natural limestone rock and other types of rock are also particularly good materials, but can be expensive when labor and transport are factored in. A combination of limestone rock embedded in concrete is a particularly good option used in some structures (see below).

For higher profile (height) reefs, metal can also be a good option. However ferrous metal has the obvious issue of corrosion and rusting, so longevity may be an issue. Non-ferrous metal like stainless steel can be cost prohibitive, and aluminum is weaker and not conducive to invertebrate growth, but may be an option for some applications.

Complex

It is safe to say that all marine species have different preferred habitat requirements for long-term survival. The more complex the structure andthe more habitats that are available (large, small, open, closed, sand bottom, etc.), then more species can call the reef home.

High, complex reefs also favor more life stages of marine life. Juvenile small fish need small spaces for survival, and adults need large spaces.

Non-polluting

All reef materials should be made from materials that will not pollute or contaminate the water and sediments below a reef. Many species of fish and invertebrates ingest and concentrate certain pollutants that can harm humans and other marine life.

Types of materials

Concrete by far is the most common material with which to build an artificial reef. Obviously, concrete will meet all the above criteria of stability, longevity, and complexity; it also has an advantage of being chemically and structurally very similar to Florida’s natural limestone reefs, known as hardbottom. Additionally, an added benefit to the reef builders is the lower cost of concrete materials.

Structures

The last piece of the puzzle is how to install these materials to produce the best habitat for fish and invertebrates. There are basically two options, 1) materials of opportunity and (2) prefabricated reef modules.

Materials of opportunity are reused waste materials that have been used before and now can have a second life as a reef. Concrete culverts are the best example of these reefs. Other good concrete material may be old bridge materials or other waste concrete. The advantage to these materials is obviously the cost, normally free to obtain, but they require heavy transport and on-shore storage.

Pre-fabricated modules are reef structures solely designed and built for use as marine habitat for artificial reefs. Although obviously more expensive per ton of materials, they offer many advantages over materials of opportunity. Structures can basically be custom built to a certain species’ life history. Certain species like gag grouper prefer ledge type habitat with cover over their heads, while others like red snapper prefer open structure to swim in and out of.

Although there are designed reefs built all over the world, we are very lucky to have two of the most prolific reef building companies available in this area. Walter Marine out of Orange Beach, Alabama offers a turn-key operation from construction and on-site storage to deployment, which has the advantage of not having to transport or store reefs in a local port for a project, making logistics much simpler. They offer about 6 different reef structures ranging from the Super Reef (15 to 25 feet tall, with an 18 feet base and up to 16 tons) to Grouper boxes or Eco-Reefs designed for juvenile fish. The Florda Special tetrahedron unit is perhaps the most common reef module in the state, which incorporates Florida limestone in the concrete walls of the reef units.

The Reef Ball company out of Sarasota, Florida has a patented concrete reef structure that is basically a hollow half ball that can be made in about 10 different sizes and weights. These are extremely stable structures that have been providing fish habitat in this area for many years.

Since 1985 OAR has been involved with the evolution of proper reef construction and incorporating the latest in new ideas and structures into our local reefs to ensure the best marine habitats available.