Be sure to read our monthly updates from Marine Savers – direct from our teams resident at
the Marine Discovery Centres at Landaa & Kuda Huraa – our long-term partnership with Four Seasons Resorts Maldives.

Reefscapers coral frame relocation mitigation "barge"

Landaa Giraavaru

At Landaa this month, we transplanted 37 coral frames, kindly sponsored by guests (28), and the Resort (nine), adding more than 3,000 coral fragments to the reef. We monitored (cleaned, repaired, photographed) a total of 563 established coral frames at various sites around the island.

Work is continuing on the generous corporate sponsorship of 50 frames (+10 Resort-sponsored) at Voavah. With the forecasted coral bleaching event (April-June), we are harvesting coral fragments from a healthy, diverse coral garden at the deeper house reef (15-18m) and replanting the completed frames even deeper (17-22m). Many thanks to our Resort colleagues at Dive and Recreation for their invaluable assistance. We have completed 20 frames, and will finish the balance later in the year once the bleaching threat is over. This will minimise stress to both the donor colonies, and the vulnerable new fragments.

To see the progress of your frame, please visit our dedicated Four Seasons monitoring page where we upload new photos every 6 months or so.

  • Coral Settlement (November 2023 Spawning) – We observed monthly declines in survivorship of our settled coral larvae, with averages of 22% for A.humilis and only 2% of A.secale recruits still alive after four months. Between “grazed” and “non-grazed” treatments, we found little difference in survivorship. It is notable that recruitment of A.secale was lower initially, so mortality of one recruit skews percentage survivorship drastically. At the end of the month, all settlement in the “grazing” tanks were moved to our outdoor open-flow tanks.
  • Gametogenesis – Large white gametes were observed in Acropora humilis, and small white gametes in A.digitifera.
  • Coral Spawning – We performed nightly monitoring snorkels around the full moon period, looking for signs of coral spawning, and observed coral spawning in the following species:
    • various species of Favites and Goneastria (at the House Reef)
    • Galaxea fasiculari and various Montipora species
    • Acropra secale, and possible Astreopora spp
Reefscapers coral propagation Maldives closeup
Reefscapers coral details

In Situ Coral Settlement Device

Our bespoke in situ coral settlement device was successfully installed at the Blue Hole site, on the north side of Landaa Giraavaru. The water on this side of the island is shallow (<2m) except for one sand-pumped Blue Hole refuge (6-8m deep) where coral frames are growing well. (Many thanks to our Resort colleagues in Engineering).

To achieve in-situ settlement of gametes released from these frames, “tents” made from tarpaulin were placed over the frames, channelling any released gametes into an open tank at the water surface. With dispersal due to wave/wind action (reducing fertilisation rates) and high mortality for coral gametes, this tank will provide a sheltered space where gametes can fertilise and successfully form larvae, which will settle within the tent. Overall, this in situ device will allow for increased settlement success.

Frames were clustered into patches, allowing maximum coral density in minimal space. The spawning device, having been in the water since October, was moved, thoroughly cleaned, and painted blue to blend in with the lagoon. The first 7mx4m tent was assembled from tarpaulin and piping, and positioned over one cluster of frames. A pipe was installed to funnel gametes into the surface tank upon spawning.

This month, no coral colonies in the Blue Hole presented mature gametes, hence no spawning was observed. We plan to make a second tent in anticipation of spawning in April to capture maximum gametes. In the meantime, we have placed a “chiller” on the spawning device, which will pump cooler water into the tent. The hope is this cooler water will protect enclosed corals from the forecasted bleaching event.

Reefscapers coral propagation healthy Maldives
Reefscapers coral spawning Maldives

Maldives Coral Bleaching Season

The ‘summer’ hot season in the Maldives runs from January to May, with March and April being particularly hot and dry. The extra hours of seasonal sunshine, combined with the current elevated global sea surface temperatures (SSTs) cause increased stresses on coral reefs (April-June), which can lead to temporary paling of the coral colonies, or even permanent coral bleaching and death.

Global climatologists are forecasting 2024 to be exceptionally hot, due to a combination of the cyclical El Niño event and the ever-increasing effects of anthropogenic climate change. Over on our Reefscapers Climate Change page, we are following developments very closely by curating the news reports from climate experts and marine scientists worldwide.

We have been tracking NOAA’s Coral Reef Watch bleaching guidelines, and over the next few weeks, the Maldives will reach “Alert Level 2”, indicating severe bleaching and significant mortality. So far, we have recorded moderate paling for some colonies along Landaa’s House Reef. We are continuing to track bleaching and will be monitoring the situation closely over the coming months.

Bleaching: Nature vs Nurture Experiment

To determine the extent to which bleaching susceptibility depends on a colony’s genetic resistance as opposed to its environment, we halved each colony on a mature, healthy frame that has grown in shallow water (3m) and planted these halves on a frame that was placed in deeper water (12m). Over time, we will monitor bleaching for both frames to see how depth might correlate with bleaching susceptibility for genetically identical colonies.

Coral Bleaching Mitigation Measures

  • Over the last year, we have been out-planting to deeper sites to minimise the damage caused by any forecasted global bleaching events. Greater depths mean cooler waters, as well as reduced UV (that exacerbates any coral heat stress)
  • Frames in the shallow house reef area, created in the last 6-18 months as part of our guest Trainee Coral Biologist program, have been relocated from 2m to 10m depth
  • We selected a series of healthy frames with a variety of species of large mature colonies, and relocated them from shallow (2-3m) sites down to 9-12m depth. Two weeks after being moved, these frames are healthy and exhibit no signs of relocation stress. 17 frames have been relocated so far, and we will continue over the upcoming weeks
  • Monitoring pictures were taken of a series of small frames for future AI analysis, to assess bleaching and mortality

NOAA’s coral bleaching forecast for Maldives as at 31 Mar.
Predicting Alert #1 (April) rising to Alert #2 (May-June).
(Right) Multi-year plot of ‘degree heating weeks’. Note that temperatures in the Maldives have now hit the coral bleaching threshold this year (black line).

Kuda Huraa

Reefscapers coral frame relocation airlift bags

This month, our Reefscapers team at Four Seasons Resort Kuda Huraa transplanted eight new coral frames, and monitored a further 302 mature frames at various sites around the island, to send out upated photos to our kind sponsors. 🙏

To see the progress of your frame, please visit our dedicated Four Seasons monitoring page where we upload new photos every 6 months or so.

Gamete Development & Coral Spawning

During March, we continued checking for mature coral gametes and signs of coral spawning. We observed immature white eggs in various Acropora species (A.gemmifera, A.plantaginea, A.nasuta). indicating that spawning will be some weeks away.

Reefscapers coral frame relocation airlift bags

Maldives Coral Bleaching Season

Many of our oldest frames with the largest coral colonies can be found in the shallow waters of our House Reef at depths of only 1.5-2m. Here, the coral frames have grown quickly and flourished, but the colonies will be very vulnerable to increasing water temperatures and light levels. Last month, we started to relocate the most vulnerable frames to the deeper Reef Crest (~10m). Using ropes and buoys, we selected the lighter-weight frames, snorkelled with them to the new site, and slowly lowered them down to the depths. Thanks to a huge team effort, we successfully moved around 100 frames in this way.

For the next stage, we needed to tackle 260 large mature frames, so we designed and built a new system we’ve called ‘The Barge’, based on a design used by our teammates at Landaa. We fixed four paddleboards together with a wooden frame, and use our small ‘whaler’ boat for towing. Out on the House Reef, we raise the coral frames up onto our floating Barge platform, drive to the top of the reef crest, and then lower them back into the water. We then use the rope and buoy method to manoeuvre each frame down to their final location at 6m depth. The Barge can hold six small mature frames per trip, and so far we have successfully relocated 120 frames. This will continue into April, along with our bleaching monitoring, which will allow us to assess the success of this project.

Many thanks to all our Resort colleagues in the Recreation, Dive, and Carpentry teams for their invaluable assistance.

To streamline our methodology for the monitoring of coral bleaching, we have added a new site, adjusted the number of colonies, and selected three specific abundant species, namely Acropora muricata (branching), A.digitifera (digitate), and A.hyacinthus (plating/tabular). We selected 15 colonies at each of our five sites, plus some colonies from last year’s monitoring, totalling 391 colonies. The colonies will be monitored every two weeks, and will continue through the next several months.

This month, we also added four new temperature loggers to the existing six already situated around Kuda Huraa. To assess any variation with depth, we have placed one logger at the deep Shipwreck site (16m), and three loggers down the reef crest (3m, 5m, 10m).

Reefscapers coral frame relocation airlift bags