Monthly report updates from our Reefscapers coral biologists at Kuda Huraa and Landaa Giraavaru.

You may also be interested in our extensive Coral Bleaching Report (2016), previous yearbooks 201720182019, and the Coral Frame Collection to view photographs of your own sponsored coral frame as part of our Reefscapers coral propagation project.

Reefscapers - NOAA coral bleaching forecast for May 2019 Maldives

Reefscapers Diary July 2020

Reefscapers coral propagation Maldives rubble substrate

Some of our Reefscapers coral frames at the deep ‘Blue Hole’ site

Monthly Progress

At Landaa Giraavaru, guest activities resumed on 15 July, and we transplanted 9 new coral frames in the final 2 weeks of the month. In addition, we also carried out monitoring tasks at the Coral Trail site, where we cleaned, repaired, and photographed a total of 76 frames.

At Kuda Huraa, we focused on updating the geo-locations and QGIS-mapping for a total of 550 coral frames at our Water Villas site. Corals in this area have started to regain their healthy colouration, and are now approximately 90% recovered. By contrast, the Channel area has been severely affected by the seasonally elevated sea surface temperatures (SST), so we plan to perform a mass retransplantation in the coming months.

Our coral frames at the deeper ‘Blue Hole’ site have escaped the worst of the bleaching, and our experimental efforts to prevent them from sinking into the shifting sand seems to be working (simply by placing rocks and rubble under the frame legs).

Reefscapers coral frames Maldives QGIS mapping


CoralWatch – Monitoring for Signs of Coral Bleaching

During July, we conducted a small assessment of the effects of the recent bleaching event on our frames. Depth is known to influence the structure of coral reef communities mainly due to light penetration, water temperature and resource availability. Additionally, exposed locations with greater water movement can reduce any increases in ambient temperature.

  • 2 locations were selected, with contrasting environmental conditions.
  • We examined the coral fragments depicted in our database of monitoring photographs taken during January and June 2020.
  • At each site, we sampled 304 Acropora coral fragments (on 8 different frames) that had been transplanted back in June-July 2019.
  • We recorded corals as ‘healthy’, ‘dead’ or ‘bleached’ (the latter including partial/complete bleaching and fluorescence).
  • Mortality was slightly lower at Anchor Point for both months (with approximately equal mortality rates).
  • No bleaching was seen in January (as expected); in June, bleaching was slightly lower at Anchor Point.

Initially, we had hypothesised that our frames at the Anchor Point site would be healthier due to the protective environmental conditions; this turned out to be true but only by an unexpectedly small margin.

Based on this snapshot of the 2020 bleaching event, the deeper outplant site only seems to provide a minimal benefit over the shallower site, although a severe bleaching event may have yielded a greater protective effect.

2020 Bleaching Assessment
% of affected coral fragments
 – S I T E –                 
Anchor Point Dive Site
Depth 15m 3m
Seabed sandy bottom solid substrate
Currents some sheltered
Mortality January 5% 8%
June 15% 17%
Bleaching January 0% 0%
June 7% 9%

Coral Plates in Aquarium One (plates KH01, KH02, KH05) and Aquarium Two (plates KH03, KH04)

  • KH01 – retransplanted with new fragments of Acropora digitifera and Acropora millepora. After some initial discoloration (normal), 90% of the fragments have now encrusted into the plate.
  • KH02 – the Galaxea fascicularis fragments remain healthy, and any paled fragments have recovered.
  • KH03 – cleaned of algal accumulation; fragments are regaining colour and the calcified areas are growing.
  • KH04 – cleaned of algal accumulation; the two remaining fragments are recovering and growing slowly.
  • KH05 – the two new fragments (transplanted in May) have regained their colouration and are healthily fusing. The older fragments continue to grow, and there is currently little competition between two colour morphs.
Reefscapers coral experiment Galaxea fascicularis Maldives

Coral Reproduction Spawning Experiment

In July, two of the smallest colonies died from competition with algae, and four colonies were observed merging (resulting in three colonies transitioning from polyp count to size measurement). Now the external ocean water has returned to normal lower temperatures, we have restarted the continuous water flow intake.

Time Lapse Experiment to Record Coral Bleaching

This month, we successfully recorded the bleaching process using our new time-lapse camera, however, the video footage was sub-optimal. The bleaching process took 5 weeks, and was eventually a result of poor water quality rather than elevated temperatures. We have adjusted our methodology and will be adding warm salt water twice daily to the closed system to elevate temperatures to accelerate the bleaching process.

‘Coral Core’ Experiment

Our in situ coral plug propagation trial has been running for over 4 months now. Some of the corals are under stress due to the recent elevated sea temperatures, and are exhibiting purple tissue surrounding both the extraction and outplant sites. Replicate-2 has seen both medium-sized fragments return to full health this month, whereas 2 of the fragments in Replicate-3 have declined in health.

R1 Plugs All 6 were lost (no epoxy) or have died (4 weeks after transplantation; due to sedimentation?)
Parent Quickly recovered from slight bleaching, new tissue growth in the cavities.
R2 Plugs 3 plugs died; 3 plugs in excellent health (regained colouration, encrusting well).
Parent Very healthy, with good recovery around and over the holes; new tissue growth in the cavities.
R3 Plugs 3 plugs now dead; 3 plugs healthy colouration and encrusting well.
Parent Very good health, with encrusting over the Epoxy for all 6 holes (but no new tissue growth.
R4 Plugs [Vertical outplanting] 2 plugs dead; 4 plugs starting to bleach.
Parent Very healthy encrusting for all 6 holes (impossible to distinguish the removal sites).
Reefscapers coral propagation Maldives healthy Acropora microphthalma

Healthy Acropora microphthalma growing on a Reefscapers coral frame

Reefscapers Diary June 2020

Reefscapers coral frame designs at Kuda Huraa

Prospective Coral Bleaching Predictions

The NOAA heat stress projections for Maldives are categorised as “Warning/Watch” in June, lowering to “Watch”during July.

Reefscapers coral frame designs at Kuda HuraaMonthly Progress

At Landaa Giraavaru this month, we monitored a total of 122 coral frames, mainly at our Blu and Anchor Point sites.

At Kuda Huraa, we monitored a total of 523 coral frames at the Water Villas site, and spent some time carefully rearranging them into a series of patterns, representing marine life in the Maldives (dolphin, seahorse, turtle, manta).

At the Water Villas site, we recorded a 30% coral mortality rate, with 17% currently recovering from coral bleaching and 53% recorded as healthy. At the Blue Hole site, corals have paled but are recovering. Some predating of Acropora digitifera is evident, thought to be caused by fish hunting for coral crabs.

The Channel site suffered badly due to the seasonally elevated ocean temperatures, with an 82% rate of coral mortality. Our limited shading experiments were able to protect some of our coral frames, which were bleached but are showing signs of recovery. By contrast, wild patches of Montipora digitata have expanded over the last year, and are now growing over some of the frames.

CoralWatch – Monitoring for Signs of Coral Bleaching

At Landaa Giraavaru, some coral bleaching remains evident around the island, but there are increasing signs of healthy recovery, particularly at sites deeper than 15m. Additionally, the Anchor Point site is subjected to strong water movement, and is home to some of the healthiest corals. (If work levels allow, we hope to provide a more quantitative assessment next month.)

At Kuda Huraa, we monitored coral frames at the Water Villas (38 frames), the Blue Hole (31) and the Channel (29), totalling 3759 coral fragments. We recorded 41% “mortality” (plus 13% “recovering”) across all 3 sites. Pocillopora fragments showed consistently higher resistance to coral bleaching when compared to Acropora species (with Acropora digitifera and A. gemmifera suffering most mortality).

Acropora Digitifera Coral bleaching Maldives

Bleaching Acropora digitifera specimen on the reef, surrounded by dead corals covered in algae

Coral Plates in Aquarium One (plates KH01, KH02, KH05) and Aquarium Two (plates KH03, KH04)

  • KH01 – all fragments died due to the seasonally elevated water temperatures.
  • KH02 – Galaxea fascicularis proved to be most resilient to the high temperatures (some paling persists).
  • KH03 – little improvement from last month; some algal overgrowth was cleaned away.
  • KH04 – only 2 fragments alive, which are slowly losing calcification; cleaned of algae.
  • KH05 – 2 coral fragments now fused; 3 fragments growing but not yet encrusted to the plate.
Reefscapers coral plate KH02

Coral Reproduction Spawning Experiment

Two additional colonies have transitioned from the polyp-counting to the size-measurement method, with 15 of the 26 colonies now having more than 30 polyps. To prevent colonies from touching the base of the aquarium, we are using sections of ceramic tile. Recently, the algal-grazing fish have been moving and sometimes overturning these, so we have increased the weight by adding extra stones (attached using an aquarium-safe cyanoacrylate).

Time Lapse Experiment to Record Coral Bleaching

A time lapse experiment has been set up to capture Reefscapers coral time-lapse photography Brinno TLC200the bleaching process in a colony of Acropora coral. Our new dedicated time lapse camera (Brinno TLC200 PRO) uses a High Dynamic Range image sensor and provides a finished time lapse video immediately after the recording ends. Complete with the BCS 24-70mm adapter, this lens is ideal for the macro video we want to capture. (Previous trials utilised a basic camera system with large video files that proved difficult to edit.)

We’ve decided to use Acropora millepora, due to its “fuzzy” appearance caused by excessive polyp activity in all photoperiods. It is hoped that this will allow a greater insight into the polyp behaviour during the bleaching process.

The camera is fixed outside the experiment tank, and is capable of recording continuously for 40 days (32GB storage, capture interval every 10 minutes).  Two aquarium heaters are installed inside the closed system to elevate the water temperature to 29-31°C. The light is supplied by one Radion XR15 PRO, with a 24-hour photoperiod at 100% intensity.

Wang et al. (2008) investigated the prolonged photoperiod and its effects on symbiont relationship. Zooxanthellae maintained a natural progression of reproductive phases for at least the first 11 hours; at hour-17, unnatural populations of phases were noted, lasting the duration of the experiment (72 hours). Zooxanthellae contained an abnormal number of chromosomes and failed to divide in an orderly fashion as would take place under natural conditions.

Junior Marine Savers

We have been developing a new coral module for the ‘Junior Marine Savers’ educational program, covering such topics as:

  • basic coral morphology and common Maldivian corals;
  • the natural formation of biodiverse coral reefs;
  • coral bleaching and other threats to coral reefs.

‘Coral Core’ Experiment

Our in situ coral plug propagation trial has been running for over 4 months now. Some of the corals are under stress due to the recent elevated sea temperatures, and are exhibiting purple tissue surrounding both the extraction and outplant sites. Replicate-2 has seen both medium-sized fragments return to full health this month, whereas 2 of the fragments in Replicate-3 have declined in health.

R1 Plugs All 6 were lost (no epoxy) or have died (4 weeks after transplantation; due to sedimentation?)
Parent Quickly recovered from slight bleaching, new tissue growth in the cavities.
R2 Plugs 3 died; 1 plug healthily encrusting, 2 plugs are surrounded by CCA (Crustose Coralline Algae).
Parent Very healthy, with good recovery around and over the holes; new tissue growth in the cavities.
R3 Plugs 2 plugs died; 4 plugs healthy.
Parent Very good health, with encrusting over the Epoxy for all 6 holes (but no new tissue growth.
R4 Plugs [Vertical outplanting] 2 plugs dead; 4 plugs starting to bleach.
Parent Very healthy encrusting for all 6 holes (impossible to distinguish the removal sites).

Reefscapers Diary May 2020

Reefscapers coral bleaching Maldives
Reefscapers coral bleaching Maldives

Examples of coral bleaching this month

Reefscapers Acropora digitifera coral bleaching Maldives (sand mortality)

Prospective Coral Bleaching Predictions

The NOAA heat stress projections for Maldives are categorised as “Alert level 1” for May, lowering to “Warning/Watch” during June.

Monthly Progress

At Kuda Huraa during May, we have been remapping and tagging our coral frames at the Water Villas and Channel sites, and monitoring wild colonies for coral bleaching. Recent stormy weather has caused some sand accumulation around our frames and even on the natural reef, resulting in mortality of various colonies.

At Landaa, 164 coral frames were monitored this month, mainly at Parrot Reef and Anchor Point sites. Each frame was cleaned and photographed, and repaired if necessary (transplanted with new coral fragments, and given a fresh ID tag).

As the monsoon has now changed from NE (hot and dry) to SW (more rain and wind) we recruited some resort volunteers to help us reposition our Kuda Huraa Water Villas frames from under the shady boardwalks back into the open lagoon. An estimated 30% of the coral colonies have died due to bleaching (and some sand drifting) and the remaining 70% are starting to regain colour and recover. Predation of some Acropora hyacinthus colonies were recorded on some frames, perhaps by large fish.

CoralWatch – Monitoring for Signs of Coral Bleaching

At Landaa, coral bleaching is being monitored in both wild colonies and our frames, however, the mortality rate appears low at present (we are continuing to monitor).

At Kuda Huraa’s Channel site, approximately 40-50% of the frames are bleached, compared to our experimental shaded frames with only 10-20% bleaching. Sand drifting has caused mortality of some colonies.
At the Blue Hole site, the corals started paling during the middle of May, but most of these are now recovering again. Coral colonies of Acropora muricata species seem to have been badly affected.
At the House Reef, little bleaching was recorded on our coral frames and the wild reef. The average temperature was 30.1°C; the lowest temperature was recorded was 28.1°C (on 29 May).

Coral Plates in Aquarium One (plates KH01, KH02, KH05) and Aquarium Two (plates KH03, KH04)

All our coral plates have been losing their colouration, due to the elevated water temperature.

  • KH01 – Bleaching was affecting more corals as the month progressed, and by 26 May all the fragments were dead.
  • KH02 – The Galaxea fascicularis are showing signs of bleaching and slow growth, but are healthy overall.
  • KH03 – The 13 coral fragments bleached heavily, although we are now seeing signs of recovery (colouration returning).
  • KH04 – 3 living coral fragments remain (1 heavily bleached, 2 showing signs of recovery)..
  • KH05 – our newest G. fascicularis plate is showing slow growth with a little bleaching, but is in good health overall.

Coral Reproduction Spawning Experiment

During May, we saw a 0% mortality rate in our juvenile colonies. We continued to combat the seasonally elevated ocean temperatures by maintaining a closed-flow system and conducting daily water changes. Whilst this prevented the colonies being exposed to continued elevated temperatures, it did expose them to daily fluctuations (within their thermal tolerance).

Multiple scientific studies have identified a direct link between thermal preconditioning and bleaching susceptibility, meaning that corals acclimatised to thermal stress or variable temperatures are shown to present a higher tolerance. We plan to conduct future trials on lab-reared colonies to establish whether this can be replicated, and possibly apply the theory to our coral frames.

‘Coral Core’ Experiment

Our in situ coral plug propagation trial has been running for over 3 months now, and by month end, 33% of the original transplanted coral plugs are surviving (8/24 comprising: 4 medium, 3 large, 1 small). From the current data, we can conclude that Medium and Large fragment sizes offer the greatest chance of success, and these two sizes will be used in future experiments. It is also clear that the chosen site for out-planting plays a vital role in the success of the transplanted fragments.

R1 Plugs All 6 were lost (no epoxy) or have died (4 weeks after transplantation; due to sedimentation?)
Parent Quickly recovered from slight bleaching, new tissue growth in the cavities.
R2 Plugs 3 died; 1 plug healthily encrusting, 2 plugs are surrounded by CCA (Crustose Coralline Algae).
Parent Very healthy, with good recovery around and over the holes; new tissue growth in the cavities.
R3 Plugs 2 plugs died; 4 plugs healthy.
Parent Very good health, with encrusting over the Epoxy for all 6 holes (but no new tissue growth.
R4 Plugs [Vertical outplanting] 2 plugs dead; 4 plugs starting to bleach.
Parent Very healthy encrusting for all 6 holes (impossible to distinguish the removal sites).
Reefscapers Acropora coral bleaching Maldives (left A.digitifera, right A.muricata)

Coral bleaching on our frames (left: A.digitifera / right: A.muricata) May 2020

Reefscapers Diary April 2020

Prospective Coral Bleaching Predictions

The NOAA bleaching heat stress projections for Maldives are categorised as “Warning” (April) and “Alert level 1” in May. This is a slight improvement compared to the predictions made earlier in the year, although June remains at “Alert Level 2”.

Monthly Progress

At Landaa, only 4 new coral frames were transplanted this month, partly due to reduced guest numbers during the global lockdown, and partly due to the pause in operations during this period of elevated ocean temperatures (newly transplanted frames are particularly at risk of bleaching).

At Kuda Huraa, 416 frames were monitored (cleaned, repaired, photographed) around the island, completing the Water Villas site. With the help of fellow Resort staff, we have moved all 500 frames at the Water Villas site, to position them in the shade offered by the boardwalks and water villas. This will lower the sunlight intensity during the upcoming period of elevated ocean temperatures. Based on last year’s coral studies, the greatest survival rates are seen on coral frames exposed to some sunlight during the day (“partial shade”). Some coral frames were left in “full sunlight” and “full shade” as comparison baselines.

We continue to experiment with shading structures at the Channel site, where 30% of our frames are showing some paling or bleaching (with a few instances of disease and tissue necrosis), and we have relocated the most vulnerable frames to deeper waters.

The graph (below) plots the temperatures recorded at the Water Villas and Channel sites (February-April), with spikes up to 34°C. The two sites have similar depths, however, the Water Villas site has lower temperatures, likely due to the stronger water currents.

CoralWatch – Monitoring for Signs of Coral Bleaching

At Landaa, we recorded species of both Acropora and Pocillopora showing signs of bleaching and stress-related coral fluorescence (down to depths of 8m, and at temperatures of 31°C). During a guest snorkelling excursion, we were able to monitor the coral bleaching status of the reefs around the inhabited local island of Kudarikilu. We recorded bleaching in various colonies of Pocillopora (5m deep, temperature of 30°C).

At Kuda Huraa’s House Reef site (12m deep), most of the corals transplanted from last month’s mass collection have adjusted well to their new environment. There are no signs of coral bleaching, despite an increase in average ocean temperatures of 1°C since early March (the maximum temperature was 31°C on 8 April). On 19 April, we checked on the healthy wild coral colonies out on the reef flat, which we had identified and tagged with buoys in March. Overall, many of the colonies had started to pale or show signs of coral bleaching (Acropora digitifera, A. hyacinthus, A. tenuis, Pocillopora verrucosa, P. meandrina, Porites species).

Coral Plates in Aquarium One (plates KH01, KH02, KH05) and Aquarium Two (plates KH03, KH04)

  • KH01 – 8 dead fragments plus 10 fragments with some bleaching or tissue loss (probably caused by the warmer intake water). The two merged Acropora hyacinthus fragments have started to grow over the digitifera, and are competing with A. cytherea.
  • KH02 – All 36 Galaxea fascicularis fragments remain healthy and continue to grow well, with healthy encrusting and no bleaching (one dead fragment from a previous month). There is some fusing between colonies of the same colour morph, but the two colour morphs are not fusing with each other.
  • KH03 – 16 fragments have died; the remaining 13 living fragments are bleaching or partially dead. Larger fragments at the top of the plate are healthier, with hyacinthus better suited to higher light levels. The A. valida fragments continue branching, but have small areas of calcification.
  • KH04 – Towards the end of April, several healthy fragments died within one week, likely due to the warmer intake water. hyacinthus variant 2 is bleaching, and variant 3 has lost tissue.
  • KH05 – Our new fascicularis plate continues to grow well, with 2 rapidly encrusting fragments; 1 fragment is partially bleached.

Voavah Frame Relocation

Over the course of 2 full days, an additional 148 coral frames were relocated to Four Seasons Private Island at Voavah (from Landaa’s Water Villas and Parrot Reef sites). Our Reefscapers staff were kindly assisted by an enthusiastic volunteer task force of Resort staff colleagues (Boat Crew, Recreation, Dive and Launch).

The new artificial reef to minimise Voavah’s beach erosion consists of 4 parallel lines of 261 relocated frames (180 Small, 42 Medium, 13 Large, 19 Hearts, 7 Diamonds). The next step will be to replant these frames with new coral fragments from Ghulifalhu (Malé Atoll).

‘Coral Core’ Experiment

The plugs and drilled holes in the parent colonies are monitored and photographed every week. The health of the corals is assessed against the Coral Watch colour chart, most recently on 26 April (9 weeks after the start of the experiment). Currently, there are no clear health differences between the tested plug sizes.

R1 Plugs All 6 were lost (no epoxy) or have died (4 weeks after transplantation).
Parent Quickly recovered from slight bleaching, but now slightly paling again due to warm temperatures.
R2 Plugs 2 died; 2 plugs are healthily encrusting; 2 plugs are surrounded by CCA (Crustose Coralline Algae).
Parent Very healthy, with good recovery around and over the holes.
R3 Plugs 1 plug died; 5 plugs healthy after 9 weeks (some slight paling is returning).
Parent Very good health, with encrusting over the Epoxy for all 6 holes.
R4 Plugs 2 plugs dead; 4 plugs starting to bleach.
Parent Very healthy encrusting for all 6 holes.

Our Reef-Monitoring AI Catamaran

After more than a year of work on artificial intelligence, we have reached an important milestone… our program successfully analysed several complete frames! The software automatically identified the taxonomic genus of the coral fragments and recorded their sizes, all without any human intervention.

This progress opens the door to ‘big data’ analyses by running the program on the whole database (20-30 days of continuous data processing). To do this, we need to make the deep learning models reliable in a wider variety of situations through additional training. We have already conducted one more batch for fragment detection and two more batches for frame segmentation (our two deep learning models).

Get the full story in our Development Journal at

Reefscapers AI coral growth analysis LG3324

AI analysis of growth (cm) of the coral colonies on frame #LG3324, over time (2017-2019)

Reefscapers Diary March 2020

Prospective Coral Bleaching Predictions

According to NOAA projections, the Maldives are currently categorised as “Bleaching Watch” (March), “Warning” (April) and “Alert Level 2” (May-June), an alarming prediction when compared with 2019, which reached “Alert Level 1” only for June.

The degree heating weeks (DHW) could potentially last 8-10 weeks, which would be devastating for much of the coral reefs in the Maldives. The warmest sea surface temperatures (SSTs) are seasonally expected during the last 2 weeks of April, and the corals could then continue to be at high risk through to the middle of June. Realistically, we should be bracing ourselves for serious levels of coral bleaching, followed by possible widespread mortality.

Coral bleaching Maldives NOAA heat stress map
NOAA Bleaching Alert Levels Maldives 2020
Monthly Progress

During March at Kuda Huraa, a total of 12 new coral frames were sponsored, and a further 38 frames were monitored (cleaned, repaired and photographed). Additionally, we spent 2 days re-mapping our frame sites around the island, and we are currently processing the ‘orthomosaic’ digital map from the data.

At Landaa, 19 new coral frames were transplanted this month, (9 sponsored by guests, 10 sponsored by Four Seasons) and a total of 154 existing frames were monitored around the island (mainly at the Coral Trail, Spa and Water Villas sites).

Monitoring at the East Blue Pit highlighted two important facts:

  • Some corals that were heavily bleached are now showing signs of recovery and growth of new branches.
  • The frames at the bottom of the pit are slowly being covered in sand, killing the lower coral fragments. All the 31 frames were lifted from the sand, but it is likely that this will keep on happening. We are trying to find a solution to prevent this, to ensure the maximum survival success for all colonies.
CoralWatch – Monitoring for Signs of Coral Bleaching

At Kuda Huraa, we have secured 7 coloured buoys to the natural reef, to mark the locations of healthy coral colonies selected for monitoring during the upcoming weeks. To provide a baseline for our coral frames, we selected a variety of wild coral species (Acropora digitifera, A. hyacinthus, A. tenuis, Pocillopora verrucosa, P. meandrina, Porites species). We have started to see some paling of corals on our frames at the Channel site. We will move the most vulnerable frames to the cooler/deeper waters at the House Reef, and we plan to experiment with some shading structures over selected frames.

At Landaa, coral bleaching was observed at the Blu and Coral Trail sites, with bleached and pale coral colonies recorded on the natural reef and our frames. Species of Acropora and Pocillopora were impacted, with Acropora colonies seen to be fluorescing (to cope with the UV-stress).

Coral Plates in Aquarium One (plates KH01, KH02, KH05) and Aquarium Two (plates KH03, KH04)

KH01 – 28 out of 35 fragments are now encrusting (a decrease from last month’s 31/37).

  • Acropora hyacinthus has started to regrow onto the plate.
  • digitifera is growing over calcified areas of A. hyacinthus.
  • cytherea continues to fuse, and appears to be dominant over A. hyacinthus.

KH02 – All 37 fragments of Galaxea fascicularis are healthy and encrusting. Colonies of the same colour morph are fusing, but the two colour morphs are not fusing with each other (despite being in contact) and are not negatively affecting the growth of each other.

KH03 – 28 out of 31 fragments are now encrusting to some extent (3 more than last month).

  • 1 of the hyacinthus fragments continues to decline in health, with some areas showing complete tissue loss. Due to the slow speed of advance, it is unlikely to be disease.
  • Both top-row hyacinthus fragments are growing well (maybe better suited to greater light intensity).
  • The valida fragments continue to grow into branching patterns, but still have small areas of calcification.

KH04 –15 out of 26 fragments are now encrusting (a decrease of seven from last month). The fragments have recovered substantially from the tissue loss in January. So far, the variants of A. hyacinthus are growing equally well together.

KH05 – out of the original 28 fragments, 10 have now started to encrust onto the plate, and the remaining fragments have all developed new corallites. Interestingly, where new corallites have grown, the tentacles of the polyps appear to have a green hue compared to the original brown colour morph of the parent polyps. This could be because they are new and have yet to accommodate the specific zooxanthellae, although brown pigment thought to be the symbiont cells have been observed in the encrusting skeletons. At the start of March, 17 new fragments were added (2 have begun to encrust).

Our Reef-Monitoring AI Catamaran

Frame Recognition – Through prolonged tuning of the parameters, we have greatly improved the results of the frame recognition algorithm. We can now successfully detect the frame structure’s position in 99.8% of monitoring photos (up from 85-90%). From the 516 test images, only a single photograph was not processed successfully.

Coral Detection – We have improved the performance of our deep-learning algorithm for detecting the coral fragments. By adding data augmentation (random rotations and flipping of the training pictures), we are now able to detect corals more accurately. Further training still needs to be done for some specific cases, such as newly transplanted fragments (which are small and difficult to detect).

Frame analysis – It has taken a lot of work to develop and improve the algorithm that matches the detected coral fragments to the bar. There are many significant algorithmic challenges, including merging data from the four monitoring pictures. The algorithm is already much more accurate, but improvements are essential to be able to track down the growth of our corals at the colony level.

Catamaran – We have installed an additional battery for the propellers, and we are currently investigating an issue with the onboard cameras. We have noticed that nearby boats can sometimes generate radio interference, so we are researching whether a 4G modem would be more reliable than the radio antenna.

Reef monitoring catamaran AI frame detection

AI recognition of the coral frame

Reef monitoring catamaran AI frame analysis

AI analysis of the coral frame

Reef monitoring catamaran AI coral identification

AI identification of coral colonies

Coral Reproduction Spawning Experiment

Reefscapers coral reproduction starting to bleachOur coral reproduction experiment is still on-going, as we assess the health of each newly settled colony each week. Bleaching was first observed on 17 March (rock 20, colony A) and two weeks later almost every colony had bleached. Filtered seawater is pumped directly from the ocean to our experimental tanks, and the March-May period is the time of seasonally increased ocean temperatures. We recorded elevated temperatures of 29.1°C to 30.2°C that likely caused heat stress in the corals.

We have now turned off the direct seawater inflow, and have started to supply stored water that has equalised to the same temperature as the tank. Cleaning is now done twice a day, siphoning out any detritus or left-over food. To help the corals cope with the absence of zooxanthellae, a daily fresh supply of rotifers is provided (along with fresh algae to feed the rotifers). A few days after implementing these adapted procedures, the first signs of recovery could be observed on some colonies.

‘Coral Core’ Experiment

The coral plugs and parent-colony drill-holes are photographed and monitored weekly, with health assessments using the CoralWatch colour chart. We now have 6 weeks of data, conducted with three different trial plug sizes. We have observed some predation, probably by parrot fish taking advantage of the increased roughness and accessibility of the coral surfaces.

R1 Plugs All 6 were lost (no epoxy) or have died (4 weeks after transplantation).
Parent Healthy, having quickly recovered from slight bleaching. Some minimal signs of predation.
R2 Plugs 2 died by week #5; 4 plugs are alive, larger ones healthier (darker); one plug (large) is encrusting.
Parent Overall health is good, with one drill-hole presenting signs of slight fish predation.
R3 Plugs 1 plug died after 3 weeks, the remaining 5 are healthy (slight paling, some encrusting).
Parent very good health, with encrusting over the Epoxy for all 6 holes.
R4 Plugs 2 plugs died by week #3; 4 partially-bleached (slow recovery after transplantation), no encrusting.
Parent Very healthy, with encrusting over the Epoxy for all 6 holes.
Voavah Frame Relocation

During the month of March, a new project was started to relocate coral frames to the island of Voavah. We plan to create an artificial reef barrier on the East side of the island, as an experiment to monitor the effects on beach erosion.

Over the course of a full day, our team of 9 biologists and divers uplifted 114 frames from the Water Villas site, and brought them to the supply jetty using the small MDC whaler boat and a raft. The selected frames were originally sponsored by Four Seasons (not by guests) and had not been recycled during last year’s major re-transplantation efforts by our volunteers. Any living coral colonies were fragmented for propagation at the Water Villas site.

We then loaded the frames onto a large dhoni and transported them across the channel to Voavah. The frames were unloaded from the boat and relocated behind the reef crest in two lines (1m-3m deep). Big thanks go out to our dedicated task force of 13 helpers from Voavah and Landaa.

In addition, a further 140 old frames will be brought from the Water Villas and Parrot Reef sites. The next step will be to replant all the frames with new coral fragments, harvested from the coral rescue project at Gulhifalhu. We plan to monitor them periodically over subsequent years.

Reefscapers Diary February 2020

Reefscapers coral frames relocation dive work Maldives

During February at Landaa Giraavaru, 24 new coral frames were transplanted (13 sponsored by guests, 11 sponsored by Four Seasons) plus a further 434 frames were monitored, mainly at the Blu site (cleaning, re-transplanting and photographing them).

At Kuda Huraa this month, we transplanted 14 new coral frames, and monitored a further 45 frames. Most coral fragments used for transplanting were harvested from our mature frames at the Channel site. In anticipation of the seasonally warmer ocean temperatures, we have started to move frames to deeper waters and to set up shading for vulnerable frames.

coral bleaching Maldives NOAA predictions
Prospective Coral Bleaching Predictions

The data projections issued by American agency NOAA aim to predict the global thermal bleaching stress for the next few months, based on the best available science.

Projections for the Maldives during March (weeks 1-4) indicated low stress for the corals, but weeks 5-12 (April-May) are at “Alert Level 2”, meaning severe bleaching and mortality is likely throughout much of the country.

The prediction for ocean temperatures during 2020 is higher than for 2018 and 2019, so we can expect the coral bleaching to be more severe this year.

The severity of the outlook will likely change as time progresses, and the NOAA projections will be closely monitored for shifts in date and severity.

We are ramping up our efforts in preparation for the higher Sea Surface Temperatures (SST) expected during April-May.

Temperature Loggers

This month, we retrieved 4 of our HOBO ocean temperature loggers from the waters around Kuda Huraa. The loggers have been measuring the ocean temperatures continually every hour, from 4 July 2019 through to 6 February 2020. We downloaded and collated the data for plotting and analysis of the average and maximum temperatures, at each site during this time period.

Using 30.8°C as a bleaching threshold (taken from NOAA’s coral reef watch benchmarks), all the average recorded temperatures from July 2019 to February 2020 are more than one degree Celsius below the bleaching threshold. All the sites had similar average temperatures (~29.3°C), and the average temperature has decreased overall since July 2019. Although average temperatures were safely below the bleaching threshold, the hottest maximum temperatures per site occasionally spiked above the bleaching threshold by an average of 2°C (the corals can tolerate this in short bursts).

Recently, the Water Villas site experienced the highest logged temperature of 33.9°C, thought to be a combination of low tide, low winds and full sun. Moving forward, the biggest risk to coral health will be if the average temperatures stay above the bleaching threshold for days or weeks at a time. These weeks are referred to as ‘Degree Heating Weeks’ by NOAA, and are categorised by duration as follows:

  • 1-4 weeks: bleaching is possible,
  • 4-8 weeks: bleaching is very likely,
  • >8 weeks: significant coral bleaching is certain, followed by death of the corals.

Our temperature loggers will be redeployed and checked regularly over the next few months, as we monitor the sea surface temperatures and prepare for NOAA’s heat stress predictions.

At the Water Villas site, we have started to clear the areas under the boardwalks. We are relocating the more established frames so we can move our newer frames to the cooler partial-shade. We have seen that “partially-shaded” corals fare better than both “fully-shaded” and “unshaded” corals, because they receive some sunlight for nutrients but avoid full UV radiation. However, due to the shallow depth at low tide (as low as 1m), the Water Villas site can still be vulnerable to thermal stress (and coral bleaching) compared to deeper sites around Kuda Huraa.

We have relocated 42 mature frames to the ‘Blue Hole’ refuge site (depth 5-6m, total 440m2). A temperature logger was deployed here, but we were surprised to discover the temperatures were not as low as we’d hoped, averaging 29.6°C for the week (with 32.5°C spikes). It will be interesting to see if this site will be able to act as a refuge in the upcoming warmer months.

At the Channel, the southern stretch of the site is shallower and warmer, so we plan to deploy ‘shade sails’ here to protect existing frames (and we will not locate any new frames here for several months). At the House Reef site, we repositioned some frames to create a new ‘snake’ shape, along with 3 new heart shapes for Valentine’s Day.

Coral Bleaching

In order to better understand coral bleaching at the local level, we started CoralWatch monitoring on 12 February. When bleached coral colonies are encountered, we will take photographs and record the relevant parameters (date, location, water temperature, depth, species affected).
We are working closely with the Dive Team to monitor the reefs and collect as much data as possible at every opportunity, throughout February to May. During the last 2 weeks of February, bleaching has been recorded at the Funadhoo dive site and around Landaa itself (Blu, House Reef, Parrot Reef). The two main coral genera present around Landaa (Acropora and Pocillopora) were found to be affected by this early bleaching. The water temperatures are averaging 29-30°C, which is generally below the bleaching threshold, so perhaps:

  • the bleached corals are less resistant to elevated temperatures (especially for longer durations);
  • there are extra stresses such as sedimentation or localised warm ocean currents;
  • there have been temperature spikes and increased UV light experienced during low tides;
  • some of the paling colonies could be fighting disease (unrelated to water temperatures).

 To mitigate against the effects of increased ocean temperatures, work is in progress to decrease the bleaching sensitivity of our coral frames. Over the past few months, we have been choosing deeper locations for our newly transplanted coral frames, placed 7m-15m depth, at Anchor Point and Deep Blu sites. During our follow-up monitoring tasks, we can see that deeper sites are showing healthy initial growth with good encrusting onto the frame.

We are also transplanting more resilient Pocillopora species for our new frames, that are known to be more resistant to heat stress and to general changes in environmental conditions.

Reefscapers Acropora coral colonies starting to bleach (left) and fully bleached (right) [February 2020, Landaa Giraavaru, Maldives]

Acropora coral colonies starting to bleach (left) and fully bleached (right) [February 2020, Landaa Giraavaru, Maldives]

Reefscapers coral refuge bleaching mitigation Maldives

Location of our deeper coral refuge sites for mitigation against coral bleaching (Landaa Giraavaru, Maldives)

Coral Plates in Aquarium One (plates KH01, KH02, KH05) and Aquarium Two (plates KH03, KH04)

KH01 – 37 fragments remaining, 31 of which are encrusting onto the plate. Interestingly, one of the Acropora hyacinthus (variant 2) fragments lost half its encrusted skeleton from the plate; under the microscope we observed the corallites surrounded by the interlinked canals of the coenosarc. Additionally, it is possible to see the individual zooxanthellae cells in areas of lower concentration.
The observable interaction between A. cytherea and A. hyacinthus (variant 1) suggests that despite the higher growth rate of A. hyacinthus, A. cytherea is more likely to win the competition for space.

KH02 – All 37 remaining fragments of Galaxea fascicularis are encrusting, and the fragments on the top of the plate are growing along the edge and back of the plate. Lifting is still visible on some of the polyps, however, this may be due to the secretion of calcium carbonate over the basal plate, rather than due to tissue loss as we originally thought (Al-Horani et al., 2005).

KH03 – 31 fragments remaining, of which 25 are encrusting to some extent, but this represents a serious decline in coral health (15 fragments lost in 2 months) perhaps due to the tissue loss in January. This affected all species, particularly A. millepora and A. digitifera (where all fragments died) except the A. valida fragments, which continue to grow well, extending branches on both sides of the plate.

KH04 – 26 fragments remaining, 22 encrusting, with good recovery after the January tissue loss. The observable interaction between A. hyacinthus variants 2 and 3 suggests that different colonies might not affect each other’s health (we will continue to monitor the interaction).

KH05 – The new Galaxea fascicularis has been growing well so far, with 7 of the 28 fragments starting to grow and encrust (transparent skeleton with new polyps, and coloured areas with zooxanthellae). Taller fragments with live polyps have been extending their skeletons downwards and developing new corallites through budding. All polyps are also extending their tentacles and are exhibiting a brown colour morph.

‘Coral Core’ Experiment

 Overall, the coral plugs and the parent colony are showing improved health after we relocated them to increase water flow and reduce direct sunlight. Encrusting has started on the edges of the plugs and the donor holes, and we expect the addition of Epoxy will close the larger gaps and further encourage encrusting.

We have been on several scoping dives to look for new sites. Site#1 consists of 2 large colonies of Porites lobata (2m diameter x 1m high, at depths of 1-5m). They both have areas of healthy living tissue (for donor plugs) interspersed with areas of bare rock (as transplant sites) that will ensure that plugs are subjected to very similar environmental conditions, which should improve the chances of survival.

Upon starting the experiment, we realised the drilling stages were tricky and very time-consuming, so we kept the total number of plugs to a minimum. Further practise and experience with underwater drilling and handling the Epoxy will improve our protocols and decrease the overall time taken.

Drilling and removal of Medium and Large plugs were found to be easier than the Small size, however the Small size will initiate faster encrusting (Medium/Large plugs take 2 months to encrust). Photos will be taken at weekly intervals and added to PhotoQuad software to calculate exact growth rates for each size class at each site. The exposed holes will also be monitored by the photographs for: encrustation, disease, predation, competition, algal growth.

Education marine biology apprenticeship collecting coral planulaeCoral Spawning Experiment

Yaniu Rauf, our current marine biology apprentice, is continuing the coral sexual reproduction experiment for his personal scientific project.
After three months, we have achieved a 75% success rate (76 surviving coral colonies, from an initial 101). Several colonies have now grown too large to continue individual polyp counts, so we will switch to recording dimensions and colour as indicators of health.

Reefscapers coral reproduction experiment

Reefscapers Diary January 2020

At Landaa Giraavaru, a total of 24 new coral frames were transplanted in January 2020 (sponsored equally by guests and Four Seasons) and a total of 191 frames were monitored (cleaned, repaired, photographed) at various sites.

At Kuda Huraa, we transplanted a total of 19 new coral frames around the island. Since September 2019, we have re-transplanted and monitored a total of 810 frames (averaging 5.5 frames per day). We continue to remove any Rhodophyta turf algae from our frames as we encounter it, to prevent the algae from blocking the light and smothering our corals. Frames in the Channel are starting to mature nicely, so we plan to use these as donor colonies, fragmenting and re-transplanting them to our new frames.

With the warmer weather approaching, we will start relocating vulnerable frames under the shade of the boardwalks, so they are partially shaded during the day. We also plan to relocate some frames into a heart shape, sited in deeper cooler waters, again to help mitigate against thermal stress.

Reefscapers coral frames closeup

Coral Plates in Aquarium One (plates KH01, KH02, KH05) and Aquarium Two (plates KH03, KH04)

Some coral bleaching was observed for a short period earlier this month, despite comfortable water temperatures of 28°C in both of our small aquaria. Acropora cytherea and A. hyacinthus variant 2 were affected the most. There has been a general decrease in competitive growth on all our coral plates, suggesting the adjacent species might not threaten to outcompete each other when transplanted onto our frames.

KH01 – 2 fragments died; 33 out of 40 remaining encrusting fragments. Competitive growth between A. cytherea and A. hyacinthus has continued to slow (neither species has a dominant growth pattern) although A. hyacinthus continues to calcify over A. digitifera (corroborating field observations).

KH02 – the Galaxea fascicularis polyps have recovered; they generally continue to grow well and bud. Some lifting and tissue loss are still visible, and one polyp has died.

KH03 – 35 out of 40 fragments encrusting onto the plate (down from 38/46 fragments last month). Six fragments were lost; A. millepora was badly affected by the water quality problems at the start of the month (A. hyacinthus is recovering; A. valida and A. cytherea seemed unaffected).

KH04 – 24 out of 26 fragments encrusting (2 down from last month); competitive growth between A. hyacinthus variants has also slowed down.

KH05 (new) – transplanted with 28 Galaxea fascicularis fragments, which we hope will grow to be as resilient as those on plate KH02.

Workshop: Global Coral Reef Monitoring Network (GCRMN) [28-29 January 2020]

During January, our coral biologist Sam Burrell attended the GCRMN workshop in Malé. Established in 1995, the main goal of the GCRMN is to gather long-term global reef monitoring data, covering hard corals and fish. The Maldives are part of the South Asia region (with Sri Lanka and India) and the workshop aimed to reinvigorate the regional network, develop inter-country communication and present findings. In brief summary:

  • David Souter (GCRMN Coordinator) – outlined goals and report objectives (assess damage to coral reefs).
  • Maldives (Minister of Fisheries) – ecological initiatives to meet a 2020 deadline on coral reef protection.
  • India – status of coral cover and species diversity; problems of sedimentation and illegal harvesting, invasive soft corals and coral diseases. Urgent need for ecologically sustainable tourism.
  • Sri Lanka – reef microbialisation and overall phase shifts from coral to algae; socio-economic and environmental impacts of coral reef loss need to be defined for legitimate policy change.
  • Maldives – (Banyan Tree, the Maldives Marine Institute and Small Island Research Group) – following the 2016 bleaching event, southern reefs are thought to have been less badly impacted. Long-term data monitoring in the Maldives is challenging, so it is difficult to assess the impacts of the fishing and tourism industries without long-term data to determine baselines.
  • There is urgent need for better-quality data on coral reefs, collected and collated regularly. How can privately employed marine biologists around the Maldives contribute to long term monitoring? Can the GCRMN provide training and sponsorship?

Online Database of Maldivian Corals

A further 4 coral species were added to our Maldivian Corals Database, bringing the total to 26 species; extra photographs and more species will be added over time. Relevant data and photographs were collated and summarised for Acropora gemmifera, Acropora pulchra, Heliopora coerulea and Porites cylindrica.

Coral Database featured image Reefscapers Maldives
‘Coral Core’ Experiment

Started last month, our experimentation with coral cores is progressing well. Most plugs are healthy, with some initial paling likely due to the extraction and transplantation process. There are signs of colonisation of the neighbouring rock, which we initially thought (but no longer think) are ‘Mesenterial filaments’there is little published research on how massive corals might grow to bridge a small gap.
‘Mesenterial filaments’ are string-like extensions of the internal folds of tissue which create the structure within a coral polyp’s body, typically bright white and full of nematocysts to capture and kill prey.

The parent donor colony now looks less healthy, likely due to an extended period in our storage tanks for (exposing it to sedimentation, fixed water flow and variable light levels). However, the scarring from plug extraction has diminished considerably and tissue recovery on the edges of the holes continues.

We are extending the experiment to an in-situ trial on the reef, with 3 lines of holes/plugs (>5cm apart) made to randomise the positioning (for water flow and light levels). We aim to locate a donor colony and outplant rock within proximity of each other to mimic environmental conditions. We will monitor on a weekly basis, with close attention to predation and to the effect of the epoxy on regrowth.

Reefscapers AI Catamaran

We have installed stronger replacement propellers for the Catamaran, and started to conduct sea trials. The propulsion system works well at slow speeds but shuts down when the propellers try to draw more power, so we have ordered a new battery. We also installed and configured the cameras, which successfully recorded underwater photographs and video.

We are making good progress with our new AI software model, which can accurately detect the position of coral frame subjects in 85% of monitoring pictures. This model is a combination of the frame-shape algorithm with new deep-learning to detect texture.

Reefscapers AI catamaran reef monitor camera install
Reefscapers AI catamaran reef monitor frame detection

Coral Spawning Experiment

Unfortunately, none of the Pocillopora damicornis planulae settled on the Education marine biology apprenticeship collecting coral planulaeoffered substrate. We observed several bleached polyps and recorded a 0% survival rate from ≈400 larvae (perhaps due to insufficient suitable substrate, or temperature fluctuations). We noticed that none of the planulae settled on the aquarium glass in this experiment (as was previously observed with P. verrucosa). We will be starting further experiments with P. damicornis with extra substrate and more controlled temperatures.

A total of 15 colonies remain from the initial settlement of P. verrucosa, with polyp counts varying from 1 primary polyp to 8 individuals. There was some competition with the faster crowing crustose coralline algae, and this interaction will be closely monitored. There is little published information, although Elmer (2016) reported that Pocilloporid species won 68% of interactions, and Pocillopora/Porites coral recruits won 50%+ of interactions with their benthic neighbours (CCA, cyanobacteria, algae, etc).

Irene's internship coral research Maldives
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