Coral communities worldwide have been suffering increasing levels of decline over the last 50 years due to pollution, disease, overfishing, ship groundings, anchor damage, unregulated marine construction, and other anthropogenic factors. In more recent years, climate change has exacerbated the situation with higher-than-normal summer water temperatures causing further stress on coral communities, resulting in a significant decrease in coral abundance and percent cover on reefs globally. Because of this, it is critical to minimize further impacts as much as possible, with coral relocation often undertaken to lessen construction impacts on coral reef communities by moving corals out of harm’s way.

CSA Ocean Sciences Inc. (CSA) is an international marine environmental consulting and survey company. Working in partnership with A-E firm HDR of Englewood, Colorado, CSA recently completed a large coral relocation project in conjunction with major wharf repairs and construction in the Commonwealth of the Northern Marianas Islands region. The repairs covered approximately 650 linear meters of wharf face and the immediately adjacent seafloor that had been colonized by a large number of stony corals over several decades. This relocation by CSA’s skilled team, in conjunction with rehabilitating previously impacted reef habitat, was intended to provide some level of mitigation for unavoidable damages likely to result from the wharf repair project.

In this case, the existing wharf face was being covered with new sheet piles, which would result in the death of all corals currently growing on the structure. To lessen overall impacts from construction activities and to prevent the avoidable loss of thousands of healthy coral colonies, CSA staff were tasked with removing up to 4,100 healthy corals and reattaching them at a nearby recipient site identified during preliminary surveys.

The coral recipient site was a previously damaged reef area more than 2,000 m distant from the wharves and in similar water depths. The site had been heavily impacted by dredging actions shortly after World War II and was comprised of exposed rock substrate, with large amounts of loose rock rubble preventing reef recovery. This area was stabilized by the placement of more than 200 approximately 1-m diameter limestone boulders in clusters to serve as attachment substrates for the relocated corals and further provided additional habitat complexity and stability to the disturbed seafloor.

Following the placement of the boulders at the coral recipient site, healthy coral colonies on the wharf face and from the immediately adjacent seafloor were carefully removed from the substrate and placed in large, submerged racks, which were partially floated and then towed to the reattachment area. Upon arrival, the corals were removed and censused before being attached to the boulders and surrounding rock substrate utilizing a cement and sand mixture. Loose rubble was also incorporated into the final structures, preventing it from further movement and subsequent damage to relocated coral colonies. Approximately 4,570 corals representing at least 31 species were removed from the potential wharf impact area and reattached. Colonies ranged in size from 5- to 10-cm small branching corals up to massive mounding Porites sp. approaching nearly 1 m diameter. CSA staff also collected and reattached more than 50 additional loose naturally occurring corals and several large elephant ear sponges found at the recipient site to prevent their loss. Following the project’s completion, a monitoring program was implemented to measure coral survival.

CSA staff have been conducting reef rehabilitation and coral relocation programs worldwide for 30 years, with more than 100,000 corals reattached on nearly 80 projects. By implementing successful coral mitigation programs, our staff are striving to help ensure the survival of coral communities wherever possible. To find out more about our coastal and coral relocation services, visit: https://www.csaocean.com/services/marine-sciences/natural-resources