ADDU Coral Relocation Project
2023-onwards

Project Background

The Maldives government is implementing a large-scale development project within Addu City, Maldives. This project requires extensive infrastructure and land reclamation work to expand existing islands and create several new artificial resort islands. The corals and marine life within these reclamation zones is irremediably smothered when sand is pumped over the seabed, along with an impact buffer as sediment drifts are carried on local currents.

REEFSCAPERS coral relocation ADDU

Project Overview

To minimise adverse environmental impacts from the government’s ADDU development project, our Reefscapers team has relocated coral colonies from the reclamation footprints and followed up with post-relocation monitoring and maintenance surveys. Donor sites were selected by Reefscapers and the Van Oord environmentalist team after reviewing the biological capacity, work safety, and accessibility of all the sites. To ensure similar environmental conditions, recipient sites were chosen within the atoll.

Our Addu team of local and international experts consists of marine biologists, boat crews, snorkellers, a dive supervisor, and a photogrammetry/mapping specialist. This is followed in later months by a trained monitoring team, performing regular snorkelling surveys, photography, and maintenance work.

REEFSCAPERS coral relocation ADDU

Weather forecasts, tides, and ocean conditions were closely monitored by boat captains and team leaders, with regular checks on the ocean currents at each site. All boats were kitted out with PPE and first aid kits, both regularly replenished, along with work gloves and ample fresh drinking water. Scuba-diving operations were not required, but we ensured both diving and emergency response plans were put in place, with each boat manned with an experienced SCUBA professional.

Safety is a top priority for our teams, especially when working long hours in the water. Our snorkel team were chosen from the local employment pool of fishermen and boat crews, with a dive group leader and safety supervisor on each boat. Swimming abilities were assessed, and team members were regularly briefed on safety and best work practices, including buddy partners, regular breaks, and maximum 6-hour working periods.

REEFSCAPERS coral relocation ADDU

Collection, Transportation, and Deployment of Coral Colonies

Whilst snorkelling, our team used hammers and chisels to carefully break off living colonies from the substrate, which were collected together on the sandy sea bed before being brought to the surface using donkeys (floating baskets) and lifted onto the waiting boats. Many of the rescued colonies were large (>50cm diameter), particularly the massives. Once boat capacity was reached, we sailed to the recipient area and corals were carefully offloaded onto the sea bed (massives) or onto waiting underwater coral frames (fragile colonies). Massive colonies were later organised in stable upright rows, and frames were towed to their final destination site.

Coral exposure to the air was minimised to reduce stress, both onboard (submerging/spraying with seawater) or by towing in metal baskets (very successful for large colonies). For each transport operation, photographs were taken to record details of the boat and corals, dates and times, and the origin/destination sites.

REEFSCAPERS coral relocation ADDU

Translocation Progression

As per the contract with Van Oord, Reefscapers completed daily reports outlining all tasks and progress updates of the work to date. Our daily progression tracked the total reported numbers of corals moved for donor and recipient sites, as well as the dates which they were translocated.

Phase #1 included the relocation of 17,000 massive and 2,300 fragile corals. Massive colonies were arranged strategically for the success of the corals and to facilitate easier monitoring, whereas the fragile colonies were attached to a total of 112 large-sized Reefscapers coral frames (located in both Meedhoo and Hithadhoo). Given the abundance of large colonies within reclamation zones, Reefscapers actually moved significantly greater numbers of corals than outlined in the contract, increasing potential survival rates.

REEFSCAPERS coral relocation ADDU

Phase #2 included the relocation of approximately 18,000 massive plus 1500 fragile coral colonies, many arranged within a large flower-shaped pattern, roughly 50m in diameter.

REEFSCAPERS coral relocation ADDU

Post-Relocation Monitoring

An initial monitoring survey was completed two weeks after coral relocation was completed, to record sizes, distributions, and counts. Further surveys will monitor overall health and mortality of the corals after 6 months. Our mapping specialist is experienced in underwater photogrammetry, and was able to create a set of 3D models using high resolution orthomosaic imagery. Many thousands of GoPro images were inputted into software (Agisoft Metashape) to construct a 3D mesh (of coral dimensions) and an orthomosaic (showing coral health). Using our 3D images, we can extract accurate geo-referenced data of the individual relocated colonies (size, count, coral type, health, etc.)

  • In total, 112 coral frames were introduced to both Hithadhoo and Meedhoo island recipient sites. In addition, 2 full-sized pyramids (7 frames) plus 3 half-sized pyramids (3 frames) were constructed at deeper sites. Photogrammetric models have been created for selected pyramids and some individual frames.
  • The seasonally warm water temperatures during April/May contributed to the stress of the corals, and some paling and bleaching was observed on both the relocated coral colonies and the natural reefs at various sites around the atoll. To establish a baseline, we randomly selected 143 coral colonies across various natural reefs for monitoring, and to make direct comparisons with translocated colonies.
  • Site selection and availability are an important component of successful coral translocation. Shallow, sandy sites will experience warmer temperatures and greater levels of coral bleaching, and deeper sites can be adversely affected by water sedimentation from nearby dredging activities.
  • The larger massive colonies are predicted to have a higher survival rate and the highest environmental value. Mature, fragile colonies are more vulnerable to mechanical damage during translocation, but we successfully transplanted many healthy coral frames to create diverse marine habitats at new sites.

REEFSCAPERS coral relocation ADDU

REEFSCAPERS coral relocation ADDU

Coral Monitoring Summary: 6-Month Stage

Hithadhoo South (H-South) and Meedhoo Tourism Zone (MTZ)

Orthomosaic Imagery was used to individually monitor and assess 10% of the coral colonies. Initial and 6-month post-relocation health scores (0-5 scale) were assigned.

The coral monitoring efforts at H-South and MTZ highlight the resilience of coral ecosystems to environmental stressors like temperature-induced bleaching. It also highlights the need for proactive management strategies, especially in the face of anthropogenic impacts like continued dredging, to ensure the sustained health and survival of these new marine ecosystems. Regular monitoring and targeted interventions are crucial for addressing specific challenges, particularly the health of smaller coral colonies that are more susceptible to environmental changes.

General Findings

  • Resilience and Adaptation : Despite the bleaching event during April-June 2023, the coral colonies exhibited remarkable resilience and recovery rates.
  • Environmental Factors : Some colonies were smothered by sedimentation (due to dredging), others were physically dislodged by strong currents.
  • Regular Monitoring : The data underscores the need for regular maintenance and monitoring.

H-South

  • Impact and Recovery : During April-June 2023, coral colonies in the H-South site experienced significant bleaching due to high water temperatures (over 34°C). Subsequently, there were notable signs of resilience and recovery post-bleaching, with an impressive survival rate of ~97% at the 6-month stage.
  • Challenges : Many colonies could not be monitored due to sedimentation and low visibility caused by ongoing dredging activity. Smaller colonies were more prone to displacement and overturning by strong currents, tides, and nearby boat traffic.

MTZ

Spanning 10 sections (MTZ-A to MTZ-J), these colonies suffered from bleaching during April-June 2023, due to water temperatures exceeding 36°C. Minimal signs of ongoing bleaching were observed during the 6-month monitoring phase.

  • Survival Rates : Post-relocation, the survival rate across these colonies was 77%. Coral health was negatively impacted by sedimentation and overturning, particularly affecting smaller colonies.
  • Common Issues : Displacement, overturning, and sedimentation were prevalent across all sections.
  • Sections MTZ-A to J: Each section had varying numbers of coral colonies, all situated in similar shallow lagoon environments. The survival rates ranged from 67% (MTZ-D) to 90% (MTZ-J).
  • Disease : To mitigate risks associated with algae, pests, and disease, all dead coral colonies were meticulously removed from the coral frames, and replaced with new coral fragments (taken from nearby partially-dead colonies). Acropora tenuis suffered heavily from bleaching and subsequent predation by Drupella snails.