Structural Restoration Methods

Structural restoration generally involves the construction of artificial reefs, sinking of wrecks, or relocating rocks/dead coral heads. The goal is to increase the amount of reef structure and habitat available for the corals and other reef organisms to grow on or live around.

Structural restoration is required in areas where the reef has been lost due to disturbances such as blast fishing, boat grounding, anchors, dredging, landslides, etc. In areas that have been reduced to rubble or sand, corals will not have solid structures to attach to and will be abraded or buried during high waves.

Natural ecosystem succession in these marginalized areas can take decades to recover, and many never do so on their own if the structure is sufficiently lost.

Natural means reef structure could return in areas with physical reef damage, including the settlement and long-term growth of corals from the Fungiidae family, which are better adapted to survive without being attached to the substrate. Eventually, these Fungiidae corals grow large and die, creating more stable substrates that coral larvae can then successfully settle on.

Larvae from the Porites or Poccilliopora genera in the Indo-Pacific or Favia fragum in the Atlantic seem to be particularly successful in recruiting to marginalized areas, as they tend to be more resilient towards physical abuse by wave action. They also tend to be brooders, who release swimming larvae that contain zooxanthellae, are settlement competent, and recruit locally – sometimes just centimeters from the parent colony.

Giant clams, rock oysters, coralline algae, and even marine debris can sometimes assist in this process. These can either add to the stabilization or expansion of existing substrate or become the nucleation point for new reefs in sandy areas.

Proactive Interventions

During structural restoration, reef managers’ interventions include adding natural substrates, stabilizing existing substrates, deploying wrecks, constructing artificial reefs, and using mineral accretion technology.

Adding natural substrate is one of the oldest forms of structural restoration. Generally, it involves adding rocks, limestone, and old coral skeletons on land back to the reef or shoreline. While these may serve multiple purposes, such as limiting beach erosion or acting as wave breaks, corals and reef organisms often colonize them. These projects tend to either require large machinery or are labor intensive. The benefits are that the materials are natural, cheap, and conducive to settlement.

Substrate stabilization involves locking up rubble and unconsolidated bottoms to rebuild the structure. Various methods have been used, including mesh, fencing, concrete, bonding chemicals, adhesives, and textiles. Mostly, these tend to be labor-intensive and expensive and have shown mixed results.

Deploying wrecks and other materials of opportunities (tanks, train cars, fishing boats, etc.) is popular in many countries to create habitat and as alternative sites for diving, fishing, or marine tourism. These can be very effective at boosting biomass and economic benefits but should be done with great care and planning. This type of restoration has often been used as an excuse to dump waste, like several tire piles deployed in the United States. Anytime that materials of opportunities are used, they should be evaluated for longevity, stability, and pollution.

Artificial reefs, by our definition, are any structures that are purposefully built using accepted materials (concrete, glass, metal, etc.) to attract marine life and provide a growing area for corals. Artificial reefs are one of the best methods of structural restoration, as they can be designed specifically for the needs and conditions of the sites and the resources available to the local community.

By adding artificial structures in these areas where the physical and biological conditions for coral growth are still good and the natural levels of coral recruitment are high, the reef can quickly and effectively be restored. In recruitment-limited areas or greatly marginalized areas, artificial structures must be ‘seeded’ with coral transplants to facilitate and speed development.

In addition to restoring damaged reefs, this technique can also be used to extend the reef boundaries, create new reefs in sand flats, improve fisheries, or create alternative dive sites to mitigate the negative impacts of marine-based tourism.

You can explore more the use and application of artificial reefs in our subsequent Artificial Reef Theory & Techniques course.

In areas where there is already an abundance of reef structure, as in reefs recently impacted by coral bleaching or disease, structural restoration is unnecessary and may be a waste of resources and time that are usually limited to community-based managers.

Instead, in those areas, it may be more prudent to implement other restoration methods, such as biological restoration.