Reefscapers Diary 2023

Coral Propagation – Monthly Progress

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At Kuda Huraa during November, we transplanted 20 new coral frames, and monitored a further 155 mature frames at various sites around the island. In addition, we retransplanted 10 degraded frames, and removed nine old frames for recoating and recycling.

At Landaa this month, we transplanted 24 coral frames, kindly sponsored by guests (nine), online (one), and the Resort (14), adding a total of 1138 coral fragments to the reef. We monitored (cleaned, repaired, photographed) a total of 139 established coral frames at various sites around the island. We have also been lifting 12 buried frames out of the seasonally shifting sands, replacing a total of 900 dead fragments.

Parrot Reef Relocation – This month, two Parrot Reef dives were undertaken, and 900 fragments were recycled in the untagged patch.

Soft Coral Propagation

This month, we started for the first time to experiment with the propagation of soft corals onto our frames, to introduce more species diversity and to create a new garden of soft corals.

We collected small fragments of Sarcophyton species from 1m depths around the House Reef’s Sea Star site. These fragments were then cut and secured to rubble substrate with simple elastic bands. We divided the fragments into two groups and continue to monitor health and growth.

• Half the fragments were directly outplanted onto our frames – many of the fragments became loose and were lost. Five fragments successfully attached, and appear to be doing well.
• Half the fragments were acclimatised in our aquarium – all but the smallest fragments successfully secured themselves to the rubble after 10 days, and we were able to remove the elastic band. We plan to outplant each ‘fragment + rubble’ onto our frames.

AI Program – Coral Growth Analysis

This month, we used our inhouse Artificial Intelligence software to analyse the latest monitoring photographs in our database. We plotted the growth rates (volume) of species of Pocillopora and Acropora corals transplanted onto all our small-sized frames at both Landaa Giraavaru and Kuda Huraa.

• During 2023 alone, volumes of Acropora corals increased from 4000 to 9000+ litres, and Pocillopora volume increased from 9000 to 15000+ litres.
• From this data, we also analysed the successful survivorship of corals (2017-2023), revealing survival rates of 80% in Pocillopora and 88% in Acropora
• Pocillopora – highest growth rates were found at shallow Landaa sites with strong wave action: Coral Trail, Parrot Reef, The Turtle, Water Villas, Blu.
• Acropora – highest growth rates at Landaa’s reef-slope sites: Dive, Blu Deep, Anchor Point.

Coral Propagation – Monthly Progress

At Kuda Huraa during November, we transplanted 20 new coral frames, and monitored a further 155 mature frames at various sites around the island. In addition, we retransplanted 10 degraded frames, and removed nine old frames for recoating and recycling.

At Landaa this month, we transplanted 24 coral frames, kindly sponsored by guests (nine), online (one), and the Resort (14), adding a total of 1138 coral fragments to the reef. We monitored (cleaned, repaired, photographed) a total of 139 established coral frames at various sites around the island. We have also been lifting 12 buried frames out of the seasonally shifting sands, replacing a total of 900 dead fragments.

Parrot Reef Relocation – This month, two Parrot Reef dives were undertaken, and 900 fragments were recycled in the untagged patch.

Mitigation Against Coral Bleaching in the Maldives

• The Shipwreck – this month, we completed three dives to monitor our 17 small test frames. Further monitoring will provide crucial information on fragment survival, attachment, and growth rates. We hope to determine whether this new deep site will be useful year-round, or if it will serve only as a temporary coral refuge during the bleaching season.
• Cage and Coral Lines – two dives this month, to re-establish our House Reef Coral Lines, fixing broken pipes, and tying loose ropes. We will soon start to transplant new fragments to broaden the pool of refuge species, sheltering from the upcoming warm season.

Coral Propagation – Monthly Progress

Parrot Reef Relocation

As part of our long-term Parrot Reef revamp project, all coral frames have now been relocated to the sheltered side of the reef. We are continuing to recycle and remap frames in QGIS before monitoring and photographing, with two team dives this month (using 900 coral fragments).

Mitigation Against Coral Bleaching in the Maldives

Climate scientists are increasingly alarmed that the world’s oceans have been slowly and measurably warming throughout 2023, and this is predicted to continue well into 2024. Forecasts are predicting a global mass coral bleaching event in 2024, comparable in magnitude to the event of 2016 (when 80% of the world’s corals were killed by elevated ocean temperatures.)

References

• Ocean Temperature Outlooks | Coral Bleaching Risk – Great Barrier Reef, Australia
• Climate Reanalyzer – Daily Sea Surface Temperatures
• NOAA: Sea Surface Temperature (SST) Contour Charts
• The 2023 state of the climate report: Entering uncharted territory

As the hottest season in the Maldives runs from January through to April, with ocean temperatures usually peaking in April to May, we have started to implement various mitigation measures to attempt to lessen the expected stresses on our propagated coral colonies. These corals will grow in cooler waters, away from the warmer temperatures at the sea surface, and with reduced threat from substrate-bound predators.

• The Shipwreck – our team has established a new deep coral refuge (at 16-20m) named ‘The Shipwreck’, where we’ve started preliminary trials to assess health and growth rates. As an added benefit, this site is also surrounded by a sandy seabed, isolated from rocky areas where Drupella and corallivorous starfish are encountered.
• Cage and Coral Lines – we have reactivated our cage and coral lines work, with several rope structures located midwater (at 8m depths) in our deep house reef, along with a metal cage structure (13m deep) with hanging ropes of Acropora and Pocillipora. Over the next few months, we will transplant more fragments and colonies onto these structures to increase species diversity.

Coral Propagation – Monthly Progress

At Kuda Huraa this month, we transplanted three new frames, kindly sponsored by guests. In addition, we monitored and repaired 84 frames, recycled 50+ old frames, and retagged 30+ frames. We also moved 110 frames at the Water Villas site to create four new geometric patterns (example in photo).

At our Pyramids (made from relocated rescue corals) we have been battling a coral disease outbreak that is causing paling and tissue loss. Similar symptoms have been observed at nearby reef Reethi Faru, suggesting that a pathogen may be spreading around N. Malé Atoll (in particular, affecting Acropora millepora and A. echinata). We are closely monitoring our Pyramids, promptly removing any affected corals, and isolating vulnerable colonies to minimise spread.

At Landaa this month, we transplanted 23 coral frames, kindly sponsored by guests (eight), online (four), and the Resort (eleven), adding a total of 1045 coral fragments to the reef. We also monitored (cleaned, repaired, photographed) a total of 646 coral frames, and lifted 20 buried frames out of the seasonally shifting sands; this recycled 300 fragments on degraded frames, plus a further 395 fragments at Parrot Reef. We have also been continuing our long-term project to restore and remap the Blue Hole site.

Montipora foliosa

This month, we had the opportunity to fragment a colony of Montipora foliosa that had been grown on a large ceramic plug by our colleagues on the local island of Fulhadhoo, where it thrives naturally to form a beautiful coral garden. Some fragments were carefully transplanted to frames at the Water Villas site (slow current), others to a breakwater frame (strong currents). Small fragments were also attached to ceramic nubbins in open-flow tanks in our Lab, to determine whether epoxy or superglue would cause any coral paling.

Coral Propagation – Monthly Progress

At Landaa during August, we transplanted 28 coral frames, kindly sponsored by guests (eight), online (two), and the Resort (18), adding a total of 1400 coral fragments to the reef. In addition, we monitored (cleaned, repaired, photographed) a total of 575 coral frames at various sites around the island.

We are continuing our large-scale recycling and maintenance work, lifting buried frames from the seasonally shifting sand, and recycling any fragments on degraded frames. This month, we raised 206 partially buried frames along the Coral Trail, Anchor Point, and Blue Hole sites, and added 1445 new fragments where necessary. Work has also restarted on one of our longer-term Reefscapers goals, restoring the Blue Hole site, lifting any partially buried frames, replacing tags and frags, and re-mapping.

At Kuda Huraa this month, we transplanted 18 new frames, kindly sponsored by guests (12), online (one), and the Resort (five). We monitored and repaired 226 frames around the island, and re-mapped the frames along the Shallow House Reef and Reef Crest sites using Garmin GPS. We have also been relocating Montipora digitata colonies at the Water Villas (to reduce competition and stress) and retransplanting any heavily stressed frames following the recent periods of coral bleaching and subsequent predation.

Over the last few weeks, our team has been working to control a disease outbreak at our Pyramids site. It appears to be white syndrome disease (WSD) presenting on some corals, with some colonies of A. millepora suffering from a different condition (patchier progression, and not banded). Any remaining healthy colonies of A. millepora have been quarantined under close observation.

Reefscapers Coral Experiments

At Landaa, we continue to work on our latest coral micro-fragmentation project plus our ongoing research into methods of attaching coral fragments onto our Reefscapers frames.

Coral Recruitment Survey

This month, we have been assessing how coral recruitment varies with depth, and we surveyed various sites around Baa Atoll (Kamadhoo, Madhirivaadhoo, Undoodhoo, Kudarikilu, Landaa Sandbank, Voavah Sandbank, Parrot Reef, Kendhoo, Funadhoo).

We used 20 quadrat (0.5×0.5m) samples at depths of 5m and 10m, and tallied up the number and genus of coral recruits. Overall, a total of 489 quadrats were sampled across the different sites, and we have started to analyse the results.

Coral Propagation – Monthly Progress

At Landaa during July, we transplanted 32 coral frames, kindly sponsored by guests (11), online (one), and the Resort (20), adding a total of 1685 coral fragments to the reef. In addition, we monitored (cleaned, repaired, photographed) a total of 351 coral frames at various sites around Landaa Giraavaru. We also lifted 25 buried frames out of the seasonally shifting sands, and added 450 new fragments where necessary, to any degraded lower bars.
In June, we had started recycling the 123 coral frames in the “tagged” patch at Parrot Reef. We completed the work this month, performing four separate dives, and adding a total of 1,700 new coral fragments to our frames.

At Kuda Huraa this month, we transplanted five new frames, monitored 143 frames, and retagged 25 frames. In addition, our team has been very busy:

• relocating 120 frames at the Water Villas (lifting some from the sand, moving others back into full sun now the seasonal bleaching risk has past)
• relocating 250+ coral frames from the Blue Hole and Sunrise sites, to create a new coral trail to aid snorkelers around our reef
• starting work to repurpose and recycle hundreds of frames at the Channel site

NOAA Bleaching Warnings for The Maldives

Promising news for Maldivian corals, as July’s increased cloud levels and precipitation have reduced water temperatures as expected (and as confirmed by our strategically situated temperature loggers). NOAA’s Coral Reef Watch shows forecasted temperatures as “No stress”. The relatively cooler temperatures led to a visibly quick recovery for many of the stressed coral colonies, both on our frames and out on the reefs.

Coral Bleaching Study – Monitored Coral Colonies

• Two scuba diving surveys, ten snorkelling surveys, seven hours of monitoring, ten hours data analysis
• Bi-weekly surveys, 300 colonies representing nine different species, on 136 separate frames across five sites
• 78% healthy, 8% pale, 2% partially-bleached, 9% partially-dead, 3% dead
• The Channel is the most impacted site, with 61% healthy colonies
• The Starfish is the least impacted site, with 83% healthy colonies
• Acropora muricata is the most impacted species (56% healthy)
• Acropora digitifera is the most resilient species (88% healthy)

Channelling Action

Each year since 2016’s global mass bleaching event, The Channel coral restoration site at Kuda Huraa has been the most affected by the seasonally elevated ocean temperatures. Land reclamation work on the adjacent local island of Bodu Huraa has significantly reduced water flow in the area, leading to increased water temperatures and higher coral mortality rates.

Our Reefscapers team has been working hard to improve the Channel coral restoration site… A big thanks to the whole team for their dedication and tireless group efforts this month. We have been replacing dead coral with new fragments from neighbouring large healthy coral colonies, relocating healthy frames to areas of higher water flow, and grouping many cleaned frames for recycling, retrieving the frame tags as we go. More than 250 frames have already been freed-up for recoating and repurposing.

In the long-term, this will make our monitoring activities easier, streamlining our coral frame database, and will create a biodiverse snorkel trail for guests to enjoy. This trail will be made of coral frames that start on the reef crest and lead inwards towards the reef flat, where the Turtle, Sea Star and Lines sites are located. These areas are teaming with marine life, creating an effective showcase of our conservation work.

Reefscapers Coral Experiments

Micro-Fragmentation – At Landaa, we restarted our coral micro-fragmentation work with two ‘massive’ coral species, Porites lobia and Favia favus. We plan to see how successfully the fragments attach to the tiles and grow, before starting experiments to explore optimal conditions for survival and growth of massive species.

Wire Coral Frame Trials – At Landaa, we have been extending our research into methods of attaching coral fragments onto our Reefscapers frames. We will try to determine if the coral fragments can self-attach onto the frame as successfully as with our current plastic cable ties method.

Coral Cover Survey

Our intern, Sol, has been taking photo-transects to assess coral cover and diversity on various reefs around Landaa Giraavaru (House Reef, Sandbank, Voavah Sandbank). While processing the photosets, we have compiled a catalogue of observed species.

Two 10m transects were taken at each of three depths (10m, 5m, 3m). We used a PVC frame to hold the camera exactly 1m away from the 50cm quadrat placed along the transect. Close-up photographs were then taken of any corals within the quadrat, to enable accurate ID of coral genera. To estimate coral cover and diversity, CPCe is used to project 25 stratified random points onto each quadrat, and corals under these points will be identified to genus level and their morphology noted.

Coral Propagation – Monthly Progress

At Kuda Huraa during June, we created three new media frames, monitored 69 frames (at the Starfish and House Reef sites), and relocated 122 vulnerable frames from the Channel.

At Landaa this month, we transplanted 30 new coral frames, kindly sponsored by guests (17) and the Resort (13), adding almost 1,400 coral fragments onto the reef. In addition, we monitored (repaired, cleaned, photographed) a total of 307 coral frames at various sites around the island. We have also been lifting any buried frames out of the sand (that shifts around the island, carried by seasonal ocean currents). We lifted 45 frames along the Coral Trail and at Anchor Point, adding 400 new fragments to degraded frames.

As part of our longer-term goals, restoration at Parrot Reef is continuing. We performed five separate dives during June, finished the QGIS re-mapping, and added 1,420 new coral fragments collected from various wild Acropora colonies from nearby reefs. Thanks to the whole team for their valuable help in this major project.

NOAA Bleaching Warnings for The Maldives

Bleaching of corals at the Water Villas and House Reef was observed in June at Landaa, following an extended period of high sea surface temperatures. Some frames were moved under the water villas and boardwalks to increase shading, and we have been monitoring to track recovery. With the onset of rainy season, we have observed re-uptake of zooxanthellae and deeper pigmentation of tissue for many colonies.

The waters surrounding Kuda Huraa were predicted to be in a “watch” state according to the forecast provided by NOAA’s Coral Reef Watch bleaching model for this month. On 13 June, we entered a “no stress” state, as the water temperatures dropped, and the corals experienced less stress. In terms of degree heating weeks (DHW), a measure of accumulated heat stress within a 12 week period, the whole month of June was characterised by a measurement of +1 DHW.

Coral Bleaching Study – Monitored Coral Colonies

The Maldives (and oceans worldwide) have been experiencing seasonally warm sea surface temperatures (SST) these past few weeks.

From our coral bleaching surveys during June, we have determined that Acropora muricata is currently the most impacted species (9% partially/bleached, 4% mortality), followed by significant bleaching of Pocillopora verrucosa.
– Acropora humilis is the least impacted species (100% healthy) followed by Acropora digitifera (73% healthy).
– Overall 54% of corals = Healthy (especially in the Deep House Reef site).
– Overall 35% of corals = Pale / 3% = Partially-bleached / 6% = Partially dead (mainly at the Channel site) / 2% = Dead

Seagrass Transplantation

Seagrass is one of the most important ecosystems in the marine environment, providing food, habitat and nursery areas for vertebrates and invertebrates alike. Seagrass meadows absorb 35 times more carbon than rainforests, despite only covering 0.2% of the ocean floor. In addition, seagrass root systems reduce the effects of coastal erosion by stabilising the seabed… literally helping to hold each of the Maldivian islands together!

Our new project will take some of the seagrass from sandy shallow waters at the Beach Villas, and retransplant it closer to the reef crest, to create a stable new seagrass meadow and biodiverse ecosystem for our coral frame gardens. We will use the ‘turf’ method to simply dig shovel-sized squares of seagrass, with substrate and roots intact. We then dig a similar-sized hole at the new location for the relocated seagrass, ensuring that roots and rhizomes are fully buried.

Coral Propagation – Monthly Progress

At Kuda Huraa during May, we monitored and mapped a total of 363 existing frames, and transplanted five new frames around the island.

At Landaa this month, we transplanted 27 new coral frames, kindly sponsored by guests (nine) and the Resort (eighteen), which in total added ~1200 coral fragments onto the reef. In addition, we monitored (cleaned, repaired, photographed) a total of 487 coral frames around the island. We have also been lifting 65 buried frames out of the seabed sand along the Coral Trail, and recycling ~600 fragments.

One of our longer-term goals for 2023 is to restore the ~300 degraded coral frames at our Parrot Reef site, where some frames had been flipped by unusually strong waves. Our aim is to relocate all the frames to a more sheltered side of the reef, re-tag and re-map the frames in QGIS, recycle fragments on all frames, and monitor the site once more. This month, we started to relocate frames into neat lines at the new site, and over four days we successfully moved a total of 135 frames. Special thanks to our Dive Team colleagues, and our apprentices (Eegan and Mode) for all their hard efforts.

NOAA Bleaching Warnings for The Maldives

Throughout May, much of the Maldives has been in a “Watch” state according to NOAA’s Coral Bleaching Forecast, implying a prolonged thermal stress on all corals in the region. In addition, water temperatures are slowly rising, suggesting more stressful weeks to come due to the accumulated heat stress (measured in ‘degree heating weeks’, DHW).

High water temperature can hinder the energy production mechanism of the algae hosted in coral tissues. Therefore, coral colonies tend to expel these non-functional algae, which are also responsible for the attractive colourations of the coral itself. When this process occurs over several weeks, corals become increasingly pale and eventually reach a bleached white colouration. With no algae to provide them with food, corals can’t produce enough energy to survive for long, and risk death by starvation.

Coral Bleaching Monitoring

With the sunny warm weather throughout much of May, we observed paling and bleaching of many Acropora colonies in the shallow lagoon along the House Reef and Water Villas sites at Landaa Giraavaru. Some coral frames were moved into shaded areas under the boardwalk and villas, to encourage faster recovery, and monitoring pictures of colonies at both sites were taken for comparison over time.

At Kuda Huraa, we conducted three dives and eleven snorkels as part of our seasonal monitoring for signs of coral paling and bleaching. Out of the 300 sample coral colonies (nine species on 136 frames at five sites) we observed 43% paling, 4% bleached, 0.3% fluorescing. The Channel is currently the most impacted location (72% bleaching), and Acropora muricata the most impacted species (58% pale, 11% bleached).

Coral Relocation Project – Pyramids of Huraa

The wider Reefscapers team have been rescuing masses of corals from a large-scale reclamation project currently underway by the Maldives government at Gulhi Falhu industrial zone. Between 3 – 11 May, many of these rescued coral colonies were transported to Kuda Huraa and retransplanted onto large frames in the form of pyramids. In total, our twenty-strong team spent more than 100 working hours in-water, transplanted ~1500 coral colonies, and constructed three large pyramid structures located in our shallow house reef.

We extend a BIG THANKYOU to our colleagues at Dive, Tropic Surf, and Launch for their invaluable assistance. The pyramids have already proven to be a great success, attracting lots of attention from staff, guests, and marine life!

This is the second time Kuda Huraa has received corals from this location; the first time being in March 2022, when approximately 10,000 colonies were relocated around the island.

Although most of the corals are recovering well from the stress of their relocation, a few colonies have bleached and died (from suspected white band disease). Fragments of Acropora muricata at the base of each pyramid have started to pale, but this is consistent with our bleaching monitoring surveys of our coral frames at other sites. In addition, a few of the rescue corals have been heavily predated by a new resident bumphead parrot fish (Bolbometopon muricatum).

Coral Propagation – Monthly Progress

At Landaa this month, we transplanted 38 new coral frames, kindly sponsored by guests (23), the Resort (12), and online orders (three), which in total added ~2100 coral fragments onto the reef. In addition, we monitored (cleaned, repaired, photographed) a total of 600 coral frames around the island. We have also lifted a total of 78 buried frames out of the sand at various sites, and repopulated with new fragments where necessary.
To celebrate Earth Day (22 April) the Resort sponsored a commemorative coral frame, which was built by guests and staff. A big thank you to everyone who came to participate and support the event. 🙏

At Kuda Huraa this month, we monitored and mapped a total of 182 existing frames, and transplanted seven new frames around the island, kindly sponsored by guests (two), the Resort (two), and online orders (three). In addition, we relocated 108 frames at the Water Villas site to provide the coral with shading and reduce stresses over the warmest period of the year.

Addu Coral Festival

Members of our team attended the 2023 ‘Coral Festival’ on S. Hithadhoo from 27-30 April (organised by the Maldives Coral Institute). Our Reefscapers stall was visited by global government representatives, NGOs, charities, international conservationists, and many interested members of the public from nearby local islands. It was an ideal platform to showcase the full range of our work to fellow marine biologists and passionate conservationists.

On the second evening, our 2023 coral spawning documentary was screened, alongside videos from the Manta Trust and the recent Nekton deep sea expedition. Throughout, our team attended various lectures, including:

• keynote presentations by prominent coral scientists Prof Callum Roberts and Prof Madeline Van Oppen
• workshops on artificial intelligence in ocean science
• panel discussions on coral restoration and conservation

Coral Propagation – Monthly Progress

At Landaa during March, we transplanted 32 new coral frames, kindly sponsored by guests (17), the Resort (13), and online orders (two), which in total added ~1200 coral fragments onto the reef. In addition, we monitored (cleaned, repaired, photographed) a total of 646 coral frames at various sites around the island.

This month, we have also been recycling and lifting coral frames around Landaa, including 12 coral frames buried in the sand at the Turtle and Blue Hole sites, and recycling 290 coral fragments at the Turtle and Bissie’s Reef.

At Kuda Huraa this month, we monitored a total of 235 existing frames (mainly at the House Reef site), and transplanted 6 new frames around the island, kindly sponsored by guests (4), and the Resort (2). We also retagged 23 frames, remapped 73 heart-formations (Deep House Reef site), and retransplanted 27 frames (House Reef and Channel sites).

Coral Bleaching Monitoring

From late March to late May, the Maldives experiences higher than average ocean temperatures. This is associated with the transition of the monsoons from the North-Easterly to the South-Westerly, resulting in calm periods with little wind and rain. These conditions can be extremely stressful for the corals, and can result in paling initially, followed by possible bleaching and eventual mortality.

Temperature loggers have been deployed at various locations to record hourly SST (sea surface temperature). We will also log additional environmental data, including: UV levels, air temperatures, precipitation, wind speed/direction.

We plan to monitor the severity of any coral bleaching, to determine which species demonstrate the greatest resilience and which locations offer the best protection. Our bi-weekly surveys will attempt to identify the external stressors by assessing the paling and bleaching of selected coral colonies:

• 300 coral colonies, on 135 coral frames, representing nine different species, at five sites around Kuda Huraa

Coral Propagation – Monthly Progress

At Landaa this month, we transplanted 38 new coral frames, all kindly sponsored by guests (18), the Resort (11), and online orders (nine), which in total added more than 2,000 coral fragments onto the reef.
In addition, we monitored (cleaned, repaired, photographed) 208 coral frames at various sites around the island.
We have also repaired frames at the Turtle site and Bissie’s Reef (using 1970 fragments), and lifted 252 coral frames that had become buried in the seasonal shifting sands (at the Turtle and Blue Hole sites).

At Kuda Huraa during February, we monitored a total of 164 existing frames, retransplanted 40 existing frames, and transplanted eight new frames around the island, kindly sponsored by guests (four), the Resort (one), and online orders (three).

Coral Thermotolerant Experiments

• Hypothesis: Coral reared at high temperature will survive best at elevated temperatures in the future.
• Key research question: Does rearing juvenile coral at higher temperatures early in the life-stage make them more resistant to higher temperatures?

In published literature on elevated ocean temperatures, less than 5% of research has studied coral juveniles. We therefore decided to run our new thermotolerant experiments utilising our newly settled Acropora secale from the November 2022 coral spawning event.

• McLachlan, R. H., Price, J. T., Solomon, S. L., & Grottoli, A. G. (2020).
  Thirty years of coral heat-stress experiments: a review of methods. Coral Reefs (Vol. 39, Issue 4).

Gamete Collection, Fertilisation and Settlement

During the November mass coral spawning event at Landaa Giraavaru, we collected gamete bundles of Acropora secale from the reef and our coral frames. The bundles were processed and allowed to fertilise in our Fish Lab. The embryogenesis stages were closely monitored, and successful settlement was observed (onto pre-conditioned ceramic coral fragment plugs). The settled planulae metamorphosed into juvenile corals, and symbiodinium (zooxanthellae) were uptaken.

Rearing at Ambient Temperature

The newly settled A. secale recruits were grown in ambient seawater temperatures (27-28°C) for around two months. We selected 28 individual juveniles from the upper surface substrate, to ensure consistency in light conditions.

Each recruit was photographed on: day 0 (T0), day 7 (T1), day 14 (T2), day 21 (T3), day 30 (T4).

To assess survivorship and health, we followed the standard bleaching category chart (Oliver, 2004) with an additional category 5 (‘dead’). After 30 days, we assessed health and survival rates.
Recruits were then subjected to seven days (T5) of elevated temperature, followed by seven days at ambient temperature. Survivorship and health were monitored and assessed throughout.

Three Thermotolerant Treatments

• Treatment 1: CONTROL (x1 tank of 28 recruits): Recruits were reared at ambient sea temperature only (27-28°C)
• Treatment 2: HOTTEST TIME OF DAY (x2 tanks of 28 recruits each): Recruits were subjected to three hours of high temperature (32°C) for 30 days
• Treatment 3: CONSTANT (x2 tanks of 28 recruits each): Recruits were subjected to 30 days of constant heat stress. The ambient temperature was increased by 1°C for five days, to reach 32°C

Results

A total of 144 recruits were assessed for this study. At 14 days (T2), survivorship remained 100% in all treatments. After 21 days (T3), all treatments had a reduction in health and survivorship. Surprisingly, the results after 30 days showed low survivorship in our control. Unfortunately, due to electrical problems, the final seven days (T5) were disrupted, giving incomplete data and inconclusive results.

Future experimental ideas:

• Re-run after the next spawning event
• Select several species to assess differences in survival and thermotolerance capacity

Coral Propagation – Monthly Progress

At Kuda Huraa this month, we monitored a total of 153 existing frames, and transplanted 13 new frames around the island, kindly sponsored by guests (eleven) and online orders (two).

At Landaa, we transplanted 62 new coral frames, all kindly sponsored by guests (44 [*]), the Resort (13), and online orders (5), which in total added 3764 coral fragments onto the reef.

[*] Guest sponsors included a very generous corporate sponsorship of 35 medium-sized frames, completed thanks to a huge team effort collecting corals, constructing frames, outplanting, and monitoring, so a HUGE THANK YOU to everyone involved 🙏

In addition, we monitored (cleaned, repaired, photographed) 199 coral frames at various sites around the island. We have also been recycling and lifting coral frames around Landaa, and retransplanting 500+ coral fragments at several of our sites (Voavah, Dive, Elephant).

Coral Thermotolerant Experiments

Over 95% of coral research studies looking at elevated ocean temperatures use adult corals (with less than 5% studying settlement, and pre-/post-settlement). We have therefore decided to start our new thermotolerant experiments utilising newly settled Acropora secale from the November 2022 coral spawning event.

• McLachlan, R. H., Price, J. T., Solomon, S. L., & Grottoli, A. G. (2020). Thirty years of coral heat-stress experiments: a review of methods. Coral Reefs (Vol. 39, Issue 4).

Read our Reefscapers Diaries for further details and photographs of our ongoing coral propagation efforts and reef regeneration experiments, both in the Lab and out in the lagoon, updated each month. You may also be interested in our ongoing research and photography, studying coral spawning.

This month, we released our coral spawning video on YouTube and social media, detailing our research and the coral spawning process here in the Maldives. To date, our video has clocked up over 1000 views!