Four Seasons Team Diaries: October 2024

At Landaa this month, we transplanted 19 new coral frames, kindly sponsored by guests (7), the Resort (11), and online (0), adding 700+ new coral fragments to the reef. We monitored (cleaned, repaired, photographed) a total of 873 established coral frames at various sites around Landaa and Voavah.

When recycling frames, dead corals are removed and new fragments attached in their place. This month, a total of 57 frames were recycled (14 small, 1 medium, 14 large and 11 heart) on the House Reef, Jetty, and Voavah frame sites, adding ~2,200 new coral fragments to the reef.

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

Coral Settlement

During November last year, gametes from 2 colonies of Acropora secale were collected and successfully settled ex situ. Following a year of growth in our Fish Lab, 10 coral recruits were fitted into concrete moulds (“coral cookies”) to hold the coral settlement plugs for cementing on the reef.
On 30 October, 5 of these recruits were out- planted onto the reef by cementing onto stable substrate on the House Reef. Recruits were planted at depths ranging from 2m-5m. Monitoring pictures were taken so that growth in situ can be monitored over time.

🗓️ Coral Spawning around the full moon of 17 October

We scheduled our nightly snorkels around this period to check for signs of coral spawning. We successfully observed coral spawning in 3 colonies of Acropora plantaginea, 11 colonies of Galaxia, and 1 colony of Acropora plantaginea, and recorded inferred spawning in 2 colonies of A.secale and 2 colonies of A.plantaginea via loss of gametes.
Interestingly, Galaxia corals are known to spawn either male or female; if spawning female, then bundles of mature eggs (pink/red in colour) are released. If spawning male, then bundles containing immature eggs and sperm (white in colour) are released. This month, we observed the release of both male and female gametes on separate days. [photos below]

🗓️ Coral Spawning around the new moon of 1 November

Again, we scheduled our nightly snorkels around this period, and successfully observed spawning in 4 colonies of Acropra loripes, and 3 colonies of Acropora (A.rosaria, A.plantaginea, A.gemmifera).

New Project on Genotyping: Tracking Resilient Coral Genetics

The global coral bleaching event earlier this year resulted in high mortality of branching corals in the Maldives (and worldwide). For successful coral propagation, we use fragments from resilient, surviving corals to re-populate the reef in the hope that this increased heat-tolerance will fare better under future periods of heat stress.

Some of our coral propagation sites suffered higher coral mortality than others, due to differences in characteristics such as depth and water flow. Surviving colonies at sites with higher overall mortality (“stress sites” of shallow water with limited flow) are more resilient than surviving colonies at other sites with lower mortality (“safe sites” of varying depth and good flow). By repopulating safe site frames with corals from stress sites, we plan to track the origin and specific placement of fragments to compare longterm survivorship.
To increase genetic diversity, we select fragments from colonies that are located far apart, and treat these as distinct genotypes.

Syntax: Recording Genotype Code of Colony from “Stress Site”

Coral coding will be structured as follows: frame number, frame face, face, bar, coral species.
– Face: face#1 displays the frame number tag; faces count in a clockwise direction.
– Bar: counts from top to bottom.
– Position: coral colony location; each bar contains 10 positions, numbered 0 to 9 (right to left).

For example: LG1000F1B3P2AAS = frame number (1000), frame face (1), bar (3), position (2), species (AAS = Acropora aspera).

‘BX’ = all bars, ‘PX’ = all positions; eg: transplanting fragments from LG1000 to all bars & positions of F1 on LG2000 = LG1000F1B3P2AAS – LG2000F1BXPX

At Kuda Huraa this month, our coral experts transplanted 5 new coral frames. We monitored and retransplanted more than 80 existing frames and repaired 3 of our large coral pyramids. During monitoring, we actively seek and remove known corallivores that eat the living corals (this month: 9 crown-of-thorns starfish, 4 cushion starfish, 787 corallivorous snails).
This month, we also conducted 27 hours of underwater monitoring over 13 days, looking for signs of coral spawning.

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.

Old Coral Frames

Since June, we have cleared, stacked and moved over 300 old frames from ‘The Channel’ (sunrise beach site). Over two days this month, we combined removing frames over land on a golf buggy with our barge method over water. We removed a further 293 empty frames, finally clearing the site. As the Channel was the main site for frames since the early days of our artificial reef project, many of the frames were over 10 years old. We therefore sorted through and disposed of irreparable frames, only moving those that could be recycled to the House Reef. Despite removing many frames from this location, there are still around 100 frames in this site. Thank you to the Dive, Purchasing, Engineering and Recreation departments for assisting us, and helping to organise a dhoni to move a large number of frames in such a short space of time.

Coral Maintenance at The Pyramids & Water Villas

Our three coral pyramids suffered some of the highest mortality rates after the bleaching event. We have continued to clear and re-populate the second and third pyramids, by harvesting fragments of different species from around the House Reef and from natural colonies at the Blue Hole. By collecting fragments from both coral frames and naturally occurring colonies, we aim to maximise the number of genotypes on the pyramids. We have continued to clear the Acropora muricata from the base of each structure, removing parts covered in algae and sponges, and re-attaching the healthy fragments. Once the base of each pyramid was repopulated, the remaining fragments were then taken and used to repopulate the Moon and Yin-Yang in the Water Villas.

While finishing the pyramids, we also worked to clear, re-populate and monitor the coral frames at the Water Villas. A shallow frame site with high temperatures, the Water Villas had a high rate of mortality due to coral bleaching. The site has also had an increase in invasive Montipora digitata coverage, Drupella spp. predation, and macroalgal blooms. These impacts have limited coral growth at this site, and altered the morphology of some colonies. We have completed 75% of the frames, and will work to complete the maintenance of this site by the end of November.

Genotype Experiment

In the aftermath of the bleaching event, we are working hard to repopulate frames with healthy, thriving corals from similar depths and conditions. This will then increase the likelihood that the frame will grow and thrive in the future, even in high temperatures. In addition to this, we will be conducting field tests on coral colonies of interest, using a method to track the genotype of each coral designed by our founder, Thomas Le Berre. Around the resort, we experienced up to 90% mortality in the shallow sites during the bleaching event. However, natural colonies of different species had a higher recovery rate. We will therefore look into these resilient natural colonies, and trial them on frames at other shallow sites around the resort.

We will focus on 3 shallow locations (1.5 – 2m) around the resort (see map below) that suffered the highest mortality rates. Although these frames will be at similar depths, the success of different coral species could vary due to the specific environmental conditions at each location. Each site will have 4 frames, 2 small frames from each of the other 2 locations. We will continue to develop and
document these frames over the next month.

Coral Spawning

The October full moon initiated the start of the second spawning period of the year for Kuda Huraa. Throughout the month, we had started to find pigmented eggs in colonies of Acropora secale and A. plantaginea (these same species were observed to spawn last October). We started our underwater spawning monitoring around the full moon period, and successfully recorded coral spawning in 36 colonies of A. secale and 8 colonies of A. plantaginea. Interestingly, unlike October 2023, we did not observe mature eggs or spawning in any colonies of A. tenuis.

We observed some gravid colonies (corals with maturing pink eggs) of Acropora secale and A. plantaginea, so we predict they will spawn around the November new moon period. White eggs were also found in some colonies (A. austera, A. humilis) in the Deep House Reef area; we will continue to track these gamete developments in November. [Photos below: pigmented eggs in Acropora secale]

Corallivores

In October, we removed a record number of corallivorous snails from around the island by optimising spawning night dives. As Drupella snails are nocturnal, they leave the reef crevices to feed at night, making them easier to find. As well as removing 551 Drupella, we also removed 201 Coralliophila violacea from both massive Porites species, and Porites cylindrica. We have also continued removing corallivorous echinoderms; the cushion star (Culcita schmideliana) and Crown-of-Thorns starfish [CoTS]  (Acanthaster planci).
We have observed a decrease in the size of the corallivores; CoTS are typically ~30cm, and cushion stars are ~19cm in diameter. This month we found a CoT only 10.5cm, and two cushion stars under 13cm. It is unclear if this is a result of us removing larger adult individuals over the year, or if this is due to the reproductive cycle. Little is known about the specific life cycles of these species in the Maldives, which is why observations like these can help fill knowledge gaps in the future.