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

You may also be interested in our extensive report on Coral Bleaching (2016), our previous yearbooks for 2017 – and – 2018, and the Coral Frame Collection gallery 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

Children enrolled in our Junior Marine Savers helping with Reefscapers coral propagation projects

January 2019

At Landaa Giraavaru, 21 new coral frames were transplanted during January (located mainly at the Dive and Al Barakat sites) and a further 350 frames were monitored (cleaned, maintained, photographed) around the island. In addition, we also relocated 250 frames under the central walkway at Water Villas, arranged into two parallel lines to provide shade from the sun during the upcoming warmer months, and to afford protection from some planned maintenance work.

Due to the recent success of our exploratory dives, we have started a new area at ‘Anchor Point’, 18m deep. It is hoped that frames placed here will exhibit increased resistance to the impending warmer temperatures, due to depth and regular strong water flow.

Reefscapers - NOAA coral bleaching forecast for May 2019 Maldives
At Kuda Huraa, we transplanted a total of 18 new coral frames and monitored a further 195 existing frames around the island. Our repeat guests have been commenting on the improvements in appearance of the corals in the Channel snorkelling area. In the coming months, we will focus frame deployment at the Water Villa site, which offers shading under the boardwalk to minimise the potential for coral bleaching (currently predicted by NOAA for the end of May).

The house reef continues to be a difficult site, as our recently transplanted Montipora fragments have been predated by fish. Acropora fragments harvested from large House Reef colonies show greater resilience to predation, but these are in limited supply. Some Crown of Thorns (COTs) were removed from the Water Villa frames; our records do show increases in COTs during this monsoonal season (December-February).

Reefscapers - crown of thorns Marine Savers Maldives

Crown of Thorns starfish eating the corals on our frames

We have been making a new starfish pattern on the western reef flat. Frames were relocated from the shallow House Reef as the coral here continued to experience heavy predation and excessive growth of macro algae.
Many of the frames are currently in poor condition and require extensive replenishing with site-specific resilient species (Acropora digitifera, staghorn Acropora, Pocillopora).

Coral Plates

The Acropora millepora coral fragments have now fused together, and the distinct boundaries are no longer visible. In addition, an encrusted Acropora tenuis seems to be overgrowing and killing the neighbouring A.millepora fragment.

Coral plate January 2019 Marine Savers Maldives

Coral plate, January 2019

Coral plate Acropora tenuis (bottom) overgrowing Acropora millepora (top)

Acropora tenuis (bottom) overgrowing Acropora millepora (top)

February 2019

At Landaa Giraavaru, 50 new coral frames were transplanted during February, and a further 250 frames were monitored (cleaned, maintained, photographed) across many of our sites around the island.

At Kuda Huraa, we transplanted 15 new coral frames (and refurbished a further 21 frames) and at Landaa Giraavaru we made 50 new frames and monitored (cleaned, repaired, photographed) a further 254 frames.

Mitigation Against Coral Bleaching

In the Maldives, the warmest part of the year predictably arrives during the dry, sunny months of March and April. This results in peak ocean temperatures towards the end of April, when the corals are at their most vulnerable, and can result in noticeable coral bleaching during April and May. We are employing various methods to monitor and to minimise the extent of the coral bleaching on our propagated coral frames.

Placement of our frames is important, with shading and depth providing lower temperatures and decreased levels of UV rays that can cause extra stress (particularly to newly transplanted coral fragments). Our water villas provide ample shade below the boardwalks, and are a good space to experiment with a variety of positions and locations across the lagoon.

Using the CoralWatch chart (right), we will conduct a pre-bleaching analysis to establish a baseline for coral colouration. Periodic surveys will then be conducted to monitor closely for signs of coral paling and bleaching. This will be followed by analyses of the data across each site and on the natural reefs close by.

CoralWatch – colour chart2

Historically, we know the newest frames (transplanted within the last 6 months) are the most vulnerable to elevated ocean temperatures. Based on NOAA predictions, it is so far unknown just how severe the bleaching will be, so transplantation of frames will continue until paling of the existing corals is observed. We will be locating most of our new frames at deeper sites (10m-18m), and using coral fragments harvested from healthy and diverse colonies in those areas. The more exposed areas with strong ocean currents will provide extra respite from any increase in water temperatures.

Known resilient species (eg. Pocillopora) will be selected in order to continue transplantation efforts, and new frames will be immediately deployed to shaded areas. If coral paling/bleaching becomes widespread, we will stop transplanting new frames, and more of our ‘younger’ frames will be relocated to the shade of the water villas. Relocating all our shallow-water coral frames from the last 6 months would be a large task, however, we do plan to relocate the most vulnerable frames around the Water Villas.

Some frames with healthy Acropora colonies will be moved to the house reef (at Kuda Huraa), to determine if established colonies can withstand the intense fish predation at the site. These frames will be closely monitored to see if other established frames can be safely relocated there. At 10m depth, these frames are less exposed to daily temperature fluctuations (as confirmed by our temperature loggers), and should be more protected from elevated temperatures. We also plan to use individual shading structures over selected frames that are more difficult to relocate (the heavier large-sized frames with healthy coral growth).

Two of our lagoon temperature loggers have been deployed in the middle of the channel (at 10m and 25m) close to Landaa, exposed to fast-moving water. The remaining two loggers were placed at shallower depths (3m and 5m) to record the sheltered reef flat surrounding the island.

Ocean temperature loggers, Landaa Giraavaru, Maldives

Ocean temperature loggers, Landaa Giraavaru, Maldives

Coral bleaching Maldives - sea temperatures, March 2013 to July 2016

Ocean temperatures in the lagoon at Landaa Giraavaru, Maldives (2013 – 2016).
Note the abnormally large spike in April 2016, that resulted in the major coral bleaching event across the Maldives (and worldwide).

March 2019

At Landaa Giraavaru, 36 new coral frames were transplanted this month, and located at the Dive site to create our new Manta Ray shape. In addition, we monitored (cleaned, maintained, photographed) a further 103 coral frames (at Blu and Water Villa sites). We have also been busily relocating 300 frames at the Water Villas, to make them more resilient to the anticipated seasonal rise in ocean temperatures (boardwalk shade and greater depth).

We have placed some experimental coral frames at the ‘Anchor Point’ site, and Hulaam (our FS Apprentice) is investigating if longer durations spent in the lagoon holding area (near the jetty) might affect the frame mortality rates at their final deployment site.

At Kuda Huraa this month we transplanted a total of 38 new coral frames, one of the busiest months on record! These were located in shade under the boardwalks at the Water Villas, and we have so far observed minimal bleaching of the new coral fragments. We also monitored a total of 210 frames around the Water Villas site, before relocating a total of 316 frames to the more shaded spots close by. These frames will remain in the shade until the sea surface temperature decreases and NOAA’s alert has been lifted, meaning the danger of coral bleaching will have passed for this year (currently estimated for May).

We have started trialling a new technique to attach coral fragments to our frames, by using natural rubber (elastic) in place of plastic cable ties. We transplanted new coral fragments to one of our flat frames, using 50% cable ties and 50% elastic, to compare any differences in coral encrusting rates. All Acropora muricata fragments transplanted with cables ties encrusted after two weeks, and early results suggest that encrusting via the elastic method is slower (possibly due to the slight movement, being less secure). This frame will be monitored closely, and we are scheduling further trials. The new technique takes some practice to master, is not as secure as cable ties, and takes more time overall, so we may limit its use to our recycled and refurbished frames.

Reefscapers aerial view coral frames [KH 2019.03] (3)

Aerial shot of Reefscapers coral frames, arranged in a geometric pattern at Kuda Huraa water villas

Reefscapers coral frame growth of macro algae

Growth of macro-algae

Reefscapers coral plate (Feb) - competition between Acropora millepora (top) and tenuis (bottom)

February

Reefscapers newly transplanted corals heavily predated

Heavily-predated coral fragment

Reefscapers coral plate (Mar) – competition between Acropora millepora (top) and tenuis (bottom)

March

Coral plate in Feb (left) and March (right), showing competition between Acropora millepora (top of each photo) and Acropora tenuis (bottom).

Coral Plates

There appears to be competition between the Acropora millepora and the Acropora tenuis specimens on our coral plate. The A. tenuis is being pushed back by the A. millepora although there are signs of tissue loss in both coral species.

April 2019

Coral spawning

On 18 April (the day before the full moon), gametes were observed in coral fragments of Acropora hyacinthus. In the following days, we harvested fragments from the reef crest to discover that the gametes were released on the night of 22 April.

There were no signs of the characteristic red coral spawn on the beach, so it’s possible the ocean currents carried it away from the island (or maybe the quantity was too low to be noticeable).

Holding Area Experiment

Hulaam has now finished his apprenticeship and completed a final presentation. He studied the length of time that our frames spend in the “holding area” after transplantation (before locating to the chosen site) and any impact on coral health.

Three coral species were identified (Acropora digitifera, A. tenuis, A. millepora), fragments collected from the same depth (0.4-0.6m) and transplanted across the 4 test frames (40 fragments of each species in total). On completion, the frames were moved immediately to the holding area (next to the jetty, at 2.4m-3.8m depth) for a CoralWatch colour health assessment rating of each fragment.

The frames were held at the jetty for either 4 or 10 days, and then moved to their new location, where health assessments were conducted on all frames every 4 days for 34 days, yielding a total of 8 health assessments for each fragment on each frame.

The investigation yielded some interesting results, so we plan to continue and expand this pilot study with the help of our internship programme and a possible Master’s thesis. Ultimately, we are hoping to use this data to improve our best practice methodologies for reducing stress on coral fragments.

At Landaa Giraavaru, we transplanted a total of 37 new frames this month (located mainly at the Blu site) and monitored (cleaned, maintained, photographed) a further 136 existing frames. We were pleased to receive a sponsorship of 10 frames by Nausicaa (Europe’s Largest Aquarium) and located them at Blu in a fish shape (to mimic their logo). We completed our frame relocation work at the Water Villas, moving a total of around 800 frames in advance of some planned resort maintenance work. 

Bleaching

Acropora species of corals have been the most affected by the seasonal increase in ocean temperatures, both naturally occurring colonies and those located on our frames. We have recorded widespread paling and bleaching across all Acropora species, but no mortality has been sighted yet so there is still time for the corals to recover once the monsoonal rains arrive. The ‘massive’ coral species appear more resilient, with bleaching only occurring in isolated colonies.

At the Water Villas, frames on the sunset side of the boardwalk show minimal bleaching (less stress) in comparison to frames on the sunrise side (brighter, more UV radiation) despite the rows of frames being only 1 to 2 feet apart.

At Kuda Huraa, guest sales were the second highest on record since 2015, with a total of 33 new frames being transplanted this month (and deployed at the shaded water villas site).

Rubber Ties Experiment

The coral fragments seem to take a longer time to encrust over the natural rubber ties (than with our usual plastic cable tie method). The fragments themselves remain slightly loose on the bar; as the rubber does not bind as tightly, the fragments can move slightly and this prolongs the encrusting process. Interestingly, Acropora digitifera fragments seem to encrust over the rubber much faster than Acropora tenuis and Acropora muricate (although our sample size of fragments is small).

Shading Experiment

We have installed a simple shading structure over one of our pale coral frames, to record how soon the various Acropora species recover. Weekly photos will be taken of the colonies, to monitor and record any colour changes.

Bleaching assessments

Along the Water Villas boardwalk, the fully shaded colonies show the darkest colouration (average CoralWatch score of 3.3) due to increased zooxanthellae; partially shaded corals score 2.8, no shade corals 2.4.

Bleaching has been most severe in the Channel area (CoralWatch score averaging 1.8) with around 80% of corals showing signs of paling or bleaching, likely due to the weaker ocean currents compared to the Water Villas site.

Coral Plates

With the warmer than usual water temperatures, we are experiencing some bleaching of Acropora species within our small aquarium. On our coral plate, Acropora hyacinthus (centre column) is completely bleached, while the same species on the right is not paling (and the A.cytherea on the left is paling). This is perhaps due to the zooxanthellae species in the centre colony being less resilient to higher temperatures.

Coral Disease

We are seeing various stages of coral paling, bleaching and mortality of our coral colonies at the Water Villas site. This appears to be caused not by the seasonally elevated water temperatures, but mainly by diseased tissue necrosis. Most of the fully shaded coral colonies have both darkened necrotic tissue with paling/bleached axial corallites.

We initially wondered if our frame relocation work might have caused extra stresses to the corals, but we have since observed the necrosis affecting a Pocillipora verrucosa frame that has been at the same location since 2016. We think that some recent dredging work on the nearby island of Bodu Huraa (now completed) stirred up sandy sediment in the lagoon, resulting in disease (either directly from the sediment, or indirectly due to increased stresses). Acropora tenuis seems hardest hit, with some monospecific frames suffering one hundred percent mortality.

Development of an autonomous catamaran to take our coral frame photographs

All the essential parts have been set up on the catamaran (propellers, battery, charge controller, Pixhawk autopilot) and using a computer we are now able to remotely control the catamaran’s movements. We plan to upgrade the charge controller to provide more power, install the cameras and a then a Raspberry Pi (an onboard computer to control trajectory).

This month, we also launched our Reefscapers AI 4 Corals campaign to expand the development and research for our pioneering robotic catamaran project.

May 2019

At Landaa, 16 new coral frames were constructed in May, and 350 frames at our Water Villas site were monitored (cleaned, maintained, photographed). At the Spa site, frames were relocated to the shade underneath the boardwalks. These frames had been recycled using existing colonies of Echinopora horrida (due to their thermal tolerance) along with a selection of species from the surrounding area that had not been showing symptoms of stress.

This month, we had the honour of building our 4000th coral frame! It was sponsored by Four Seasons, and the Resort Managers assisted with the transplantation. This marks the success of our coral propagation program, and our faithful collaboration with Four Seasons to enhance conservation efforts for corals and marine life.

At Kuda Huraa, we transplanted 5 new frames this month (historically, May is often a quiet month) and recycled 10 of our older frames. Due to the continued elevated ocean temperatures, we have been using more robust coral species (Pocillopora, Porites, Montipora) and immediately deployed them in shaded areas under the boardwalk. We also monitored (cleaned, maintained, photographed) a total of 60 frames at the Channel site.

Zooxanthellae Comparison

Acropora pulchra has previously been observed to be one of the first species to exhibit signs of bleaching, and this was observed at the Channel site, however, one mono-specific A. pulchra frame (unshaded at the Water Villas) appeared to get darker (healthier) during this period. Under the microscope, we confirmed that the Water Villas coral had a much higher density of zooxanthellae compared to that in the Channel (may be due to genetic variation between corals, or between the zooxanthellae, or maybe differing environmental conditions such as water current).

Bleaching Assessments

The sea surface temperature has been consistently recorded at 30°C for the latter part of May. Bleaching has been recorded at all locations, with varying states of severity, and mainly affecting Acropora species. Two species selected for frame building/recycling efforts, due to their relative abundance and apparent resistance to thermal stress, are:

  • Echinopora horrida – listed as ‘near threatened’ by the IUCN Red List, it is found in two main locations around Landaa: at the Spa (on several frames) and at Parrot Reef (natural colonies).
  • Heliopora coerulea – listed as ‘vulnerable’ by the IUCN Red List with a decreasing population trend, it is a member of the Octocorallian soft corals (subclass Alcyonaria). Commonly called the ‘Blue Coral’, it is one of only two types of Octocorals that calcify an external skeleton (the other is Tubipora musica). Its common name is derived from its ability to extract iron from the surrounding water, which it forms into a blue salt that is incorporated into its skeleton. There are several large colonies (>1m across) around Landaa but they grow characteristically in vertical plates, which is a drawback for coral propagation.

CoralWatch Surveys

We have been continuing our CoralWatch bleaching surveys, with a new category of ‘0’ to represent dead colonies (in addition to the normal colour range, 1 = bleached, 6 = dark).

The health of the corals declined significantly over the April-May period, with the unshaded frames at the water villas site in the worst condition (score 0.5) plus many mortalities. This was followed by the newer frames in the southern channel (0.9) and older frames at the northern channel (1.2). The completely shaded (1.4) and partially shaded (1.5) frames at the water villas fared better, as did the corals at the starfish site (the latter, with resilient Pocillopora).

The scores were also recalculated to exclude dead colonies (scores of 0) to highlight the positive effects of shading:

  • Unshaded corals are the palest (1.6)
  • Partially shaded corals are intermediate (2.2)
  • Completely shaded corals the darkest (3.4)
  • Natural reef bleaching is the same as last month (2.2)

The average light codes (palest area) were calculated for all species across all sites (excluding shade):

  • Most resilient coral species: Pocillopora verrucosa (1.7), Isopora palifera (1.4), Acropora digitifera (1.2)
  • Least resilient coral species: Acropora latistella (0.4), surprisingly, one of the few survivors of the 2016 El Niño
  • Interestingly, Acropora millepora seemed to be healthier in unshaded locations rather than shaded maybe due to genetics or local conditions (see below).

Shading Experiments

During April, we installed a shading device over one of our medium-sized coral frames [KH2278, August 2018], and have been monitoring it regularly. Some of the Acropora species are showing signs of recovery since being shaded, whilst other species are not:

  • Acropora austera is regaining colour on the upper sides (exposed to sunlight);
  • Acropora humilis and Acropora latistella have continued to bleach;
  • Acropora tenuis has died and is overgrown with algae.

We installed a second shade-device over a large-sized frame (originally transplanted in February 2018) with mature colonies of bleached Acropora, and we continue regular colour monitoring. A third shade-device was placed over four small frames, also with large colonies of bleached Acropora. Interestingly, fish species have started aggregating under the shading devices, including Batfish (Platax orbicularis), Blue-striped snapper (Lutjanus kasmira), and Long-nose Emperor (Lethrinus olivaceus).

Coral Mortality and Recovery

A mortality assessment was carried out on 50 coral frames at the Water Villas and Channel sites, with similar results on average:

  • 35% of the corals were ‘alive and healthy’,
  • 16% were ‘alive but bleached’,
  • 11% were ‘partially dead’ and unlikely to survive,
  • 38% of corals suffered mortality.

New frames (made in the last three months) had a higher amount of bleaching, but a lower average mortality (highly variable, 11% to 68%) due to exacerbating factors making recovery less likely (higher sedimentation in the Channel, ‘white disease’ at the Water Villas).

The NOAA coral bleaching warning has now ended, so we expect cooler ocean temperatures from the end of May onwards (as recorded in previous years). Given this, some of the bleached coral should be able to recover and we will be continuing our mortality assessments to determine the true scale of this bleaching event.

Reefscapers - NOAA coral bleaching outlook for Maldives improving June 2019 [KH 2019.05]

Coral Plates

A new coral plate has been made for Aquarium two with health fragments from five different species that will be monitored for merging and competition in the upcoming months: Acropora cytherea, A. valida, A. millepora, and Acropora hyacinthus (variant 1 and 2).

The original coral plate is still experiencing some bleaching due to the elevated temperatures of the water intake from the lagoon:

  • Acropora hyacinthus is suffering from mortality (the bleached fragments are overgrown by algae).
  • Acropora cytherea has regained colouration and is encrusted further across the plate.
  • Acropora hyacinthus (variant 2) remains dark, with highly concentrated zooxanthellae.

Coral Fluorescence

Several colonies were observed displaying ‘fluorescence’, which is a clear indicator of stress. Initial bleaching due to increased water temperature naturally leads to a decrease in zooxanthellae concentrations, which results in exposure to more intense sunlight. The coral compensates for this by increasing the production of colourful pink/purple protein pigments, which act like a ‘sun screen’. (This adaptation is also evident in areas of damage or areas of growth, such as branch tips).

The white skeleton also reflects much of the light. This increased light intensity represents a danger for the algae looking to colonise the new growth areas, which is mitigated by the coral producing the screening pigments. It is suggested that this shading enables the algae to enter the new tissue and establish the symbiotic association. In bleaching events, this fluorescence can be said to be a survival technique by the colony to cope with warming temperatures and the associated zooxanthellae loss.

Differences in genetics means that not all corals in the same environmental conditions will be the same colour, and colony survival within the same species can be different. Two colonies of Acropora tenuis were observed displaying fluorescence. As an experiment, one (small) colony was split into fragments and attached to a frame (LG2367) and the second (larger) colony was relocated in its entirety. It was expected that the reduction in light intensity (due to the boardwalk shading) would enable recolonisation by zooxanthellae and recovery to health. Twenty days later, whilst the complete colony showed a promising 60% recovery, all the fragments had died (possibly due to the stress of the procedure).

June 2019

At Landaa, 18 new coral frames were transplanted in June, 30 existing frames were replanted, and a further 82 frames were monitored across all our sites around the island. We also relocated 250 frames at the Water Villas site due to ongoing maintenance work.

At Kuda Huraa, we transplanted 9 new coral frames during June, and started to replenish those frames adversely affected by the recent high ocean temperatures. Towards the end of the month, wild coral colonies were visibly regaining their natural colouration and recovering from the bleaching event. Some frames were deployed to the deepest part of the channel (3m) and subsequently showed minimal bleaching, indicating that normal transplantation activities could safely resume.

Reefscapers - coral frames moved from shade after the heatwave Maldives
Reefscapers Maldives coral bleaching mortality by species 2019

Coral bleaching mortality by species 2019

Reefscapers - geometric coral shape recreated in June Maldives

Water Villa Frames
As the water temperature has stabilised and most coral has recovered from bleaching, the water villa frames were moved from the shade, back to their original locations alongside the main boardwalk. The geometric shape and flower patterns were recreated and photographed with a drone.

Coral Bleaching – CoralWatch Surveys
The CoralWatch data served well as a tool to measure the mortality of different species, enabling quantitative comparisons across sites at the Channel (June) and the Water Villas (May).

  • Mortality summary: Water villas 57%, Channel 77%, Acropora cytherea & A.valida 100%, A.tenuis 89%.
  • Acropora digitifera and A.gemmifera were most resilient species, followed by: A.austera, A.pulchra, A.humilis, Pocillopora verrucosa.

Shading Experiments

During June, the shade device over the four frames was removed. In future, shading experiments would need to assemble the shade structure well in advance of the increase in water temperatures.

KH2074 (large frame) – suffered mortality on the top bars, whilst the lower bars are recovering (the bleached Acropora muricata zooxanthellae are returning).

KH2278 (originally shaded) – Acropora austera is continuing to darken back to the original healthy colour. Comparing to adjacent unshaded frames (bleached), the shade sail seems to have successfully assisted in the recovery of these coral colonies. However, the Acropora humilis and Acropora tenuis colonies suffered 100% mortality, and the Acropora latistella colonies are alive but with bleached branches (zooxanthellae are visible at the centre of the colonies).

In-vitro Experiments

At Landaa, our new aquarium lights (Radion XR15wPro) have been installed across 5 experimental tanks and are currently set to replicate the natural reef conditions for acclimatisation. We have also made our first coral plate (similar to Kuda Huraa) using Acropora tenuis fragments, and monitored by 2 cameras (one macro, one wide angle) recording 2 short sequences daily.

Reefscapers - GIS island mapping Maldives for corals

Digital GIS mapping of our coral frames at Landaa Giraavaru

Temperature Loggers

At Kuda Huraa, we removed all our temperature data loggers from the lagoon to extract the data. The abnormally high ocean temperatures reached their peaks during the afternoons of mid-April (10th to 17th). The House Reef recorded the lowest average temperatures, whilst the Water Villas recorded the single highest temperature at 36.8°C (the strong ocean currents clearly did not reduce surface temperatures). The average temperatures at the House Reef site were often more than 1°C below the other sites and almost completely escaped the bleaching, mainly due to the great depth (13m).

Site          : Max peak (°C)  / Max daily avg (°C)
House Reef    : 31.4 on 17 Apr / 30.1 on 15 Apr
Channel North : 33.6 on 13 Apr / 31.5 on 13 Apr
Channel South : 34.6 on 10 Apr / 31.7 on 13 Apr
Turtle        : 34.7 on 12 Apr / 31.6 on 12 Apr
Water Villas  : 36.8 on 11 Apr / 31.6 on 11 Apr

The May 2019 temperatures of 31+°C were higher than in 2017-2018, perhaps an indication of this year’s prolonged “warm season” driving the coral bleaching and resulting mortality. Climate scientists have attributed the temperature spike of April-May 2019 to a regional marine heatwave, and not a major climatic event (the Indian Dipole remained neutral and El Niño was not in effect).

July 2019

At Kuda Huraa, 23 new coral frames were transplanted and deployed to the Water Villa and Channel sites. We are using both Acropora and Pocillopora species for increased resilience against environmental stressors. The House Reef site has now been completely replenished (with Pocillopora and some Acropora fragments) and monitored (maintained, cleaned, photographed).

The Water Villas site has been monitored and remapped using new aerial photographs for accurate location mapping. From aerial photographs in 2018, we have also been able to observe:

  • the seagrass bed (sunset side) has receded, likely due to sand movements around the island
  • wild reef patches of Montipora digitata have expanded in the last year
  • areas of algae have reduced, likely due to expansion of the nearby local island of Bodu Huraa. This area of algae was being farmed by ‘Dusky Gregory’ fish (Stegastes nigricans), a territorial species and therefore also useful in protecting our storage of harvested coral colonies from corallivorous fish predators.
At Landaa, 36 new frames were transplanted, and a further 231 frames were monitored across the Blu, Coral Trail and Dive sites. At Blu, we created a new ‘Stingray’ shape in the deeper water, and a total of 130 recycled frames have been given new frame codes for addition to the current database. Due to the ongoing maintenance work at the Water Villas, the whole team has been working very hard to relocate hundreds of frames away from the boardwalk to allow for the renovations (now completed).

August 2019

At Kuda Huraa this month, 14 new coral frames were transplanted into the lagoon, and the Reefscapers team have been busy with various housekeeping duties in anticipation of the new coral biologist’s arrival in September. Ninety coral frames were retagged in the Channel site and work at the Starfish site included retransplantation and remapping. Another database clean-up was completed, and frames were updated with new coordinates following the recent relocation tasks.

At Landaa, 26 new coral frames were transplanted and located mainly at the Anchor Point site, while a further 189 frames were monitored (cleaned and photographed) mainly at the Parrot Reef site.

Coral Plates

A new coral plate has been made (Aquarium One), with only Galaxea fascicularis (a fluorescent green variant and a brown variant). The plate was created by drilling each hole to match the diameter of the fragment; they are looking healthy so far, with extended tentacles and one fragment has started to encrust.

28 fragments on last month’s coral plate (Aquarium One) have started to encrust, with a further 19 still to encrust (several other fragments have dislodged). The Acropora hyacinthus is taking longer to calcify compared with lower fragments with less light. Only the Acropora digitifera specimens remain a healthy golden brown colour, all other species/variants appear to be paling.

The coral plate in Aquarium two is growing well, with 43 encrusting fragments, 5 not yet encrusted, 2 dead, and 23 missing fragments.

  • Acropora digitifera – taking longer to encrust. Fragments at the top of the plate (closest to the light) are calcifying and spreading their skeleton faster than those towards the bottom (less light).
  • Acropora cytherea – two of the fragments have fused together.
  • Acropora millepora in row “a” – little change over 10 weeks; remain white, with no corallite growth on the calcified area. It is at the bottom of the plate (less light).
  • Acropora hyacinthus in row “b” and “c” – encrusting well. Interestingly, a partially shaded area (red circle) on one of the coral fragments does not have live polyps or zooxanthellae. All fragments secrete calcium carbonate, but sufficient light levels seem to trigger the formation of corallites and uptake of zooxanthellae within the tissue.
Reefscapers coral frames - marine life Maldives

Special Volunteer Program – Coral Restoration/Replanting (meet our Volunteers @Reefscapers Instagram)

To help out with our ever-expanding Reefscapers coral propagation project, we have recruited an international team of volunteers who will be working with us for 3 months, sponsored and hosted by Four Seasons. Each volunteer was chosen for their dive skills and passion for the environment, and our extended new team will be a great help in recycling many of our old coral frames and relocating frames to new sites around the island.

Mapping of the frames located at Blu to Al Barakat was done prior to the volunteers’ arrival by lead volunteer Louise Sabadel. It took 10 days to map a total of 757 frames, plus 270 old frames were given new tags (RE tags for ‘Recycled’) for future addition to the current frame database and monitoring cycle.

The 8 volunteers arrived between 7-15th August, and following a program introduction, coral fragment transplantation training and orientation dives, replanting began straight away.

By the end of August, a total of 803 frames were replanted with corals (Acropora and Pocillopora species), an impressive average of 49 frames/day with an average daily workforce of 7.7 people.

Harvesting of coral fragments is performed daily by 4 people, collecting 2 buckets of Acropora plus 2 buckets of Pocillopora species from around the island, from depths of 2 to 8m.

Reefscapers Volunteers Maldives - helping with coral propagation
Reefscapers Volunteers Maldives - helping with coral propagation

September 2019

At Landaa, 22 new frames were transplanted during September, and a further 531 existing frames were replanted and renewed as part of our 3-month volunteer program. In fact, our coral restoration efforts have been so successful that we have completely exhausted our stocks of cable ties at Landaa! 😊

  • Replanting work was completed inside the Jetty area (200 frames) and is continuing at the Dive site.
  • 500 recently recycled frames (August) were monitored and photographed at the Al Barakat, Parrot Reef and Dive sites.
  • 280 frames have been relocated around the island for increased resilience to bleaching, and moved from shallow (1-2m depth) to deeper sites (6-9m). At the Dive Site, 500 extra frames have been cleaned, making them ready for transplanting as soon as the cable ties become available next month.
  • To date, a total of 1434 frames have been successfully replanted with corals, mainly those that had died during the devastating 2016 global coral bleaching event.
Reefscapers coral reef propagation Maldives replanting by Volunteers

Our new coral biologist, Sam Burrell, started at Kuda Huraa on 1 September, and received 5 days of program training as part of Hannah’s handover. Training included a combination of field work and database tutorials, such as monitoring and mapping frames, coral collection and transplantation, navigating QGIS, and updating the master Excel database. Hannah also walked through the Reefscapers methods and procedures manual with Sam, discussing details like ordering tags and materials, dealing with frame bookings and build-a-reef, and priorities for the upcoming months. Duties have been steadily added for Sam as the month of September has progressed, and he has become more comfortable with the program heading into October.

Our coral staff and volunteers have transplanted approximately 4,200 coral fragments in September, including:

  • 14 new coral frame sponsorships for the month;
  • 33 newly recycled frames at the Water Villas;
  • approximately 150 monitored frames (repaired, retransplanted, photographed).

Our two Reefscapers volunteers at Kuda Huraa, Sorin and Martyna, arrived early September. They have been gradually trained in coral collection and transplantation protocols, including frame cleaning, frame recoating, and general field material maintenance. They have both been hard at work and have done many of their duties independently, fulfilling September’s goal of volunteer training. Sorin and Martyna will also be able to help train any additional volunteers we add in the upcoming months.

We have been busily cleaning (and recoating) hundreds of frames for retransplanting around the Water Villas and Channel areas. The harvested fragments we have been using are the more bleach-resistant species of Pocillopora and Acropora, mostly transplanted within hours of harvesting, with excess coral fragments being stored for up to a few days. However, we had an issue with rapid necrosis in our coral storage tanks (for both Pocillopora and Acropora), and we unfortunately lost several days’ worth of coral fragments. The culprit was likely bacterial build-up, so we are improving our procedures to include:

  • more frequent, thorough cleaning of the nets, tank walls, buckets and gloves;
  • separation of the two coral genera;
  • decreasing the time taken from harvesting to storage;
  • additionally, cleaning any Drupella snails from the corals.

Coral Attachment Experiments

We continue our experiments into alternative attachment methods for our coral fragments.

  • Using Raffia (palm tree) fibres proved to be very time-consuming, and the fibre ends up covering a large area of coral tissue. After 18 days, the coral fragments were still attached to the frame, but they have not encrusted and appear to have died.
  • Using rubber was also more time-consuming than cable ties, and the fragments could only be loosely attached to the frame. After 14 days, the coral fragments were all still attached; they showed signs of encrusting over the rubber tie, but not encrusting onto the frame.

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

Generally, Acropora hyacinthus seems to be encrusting faster than the other Acropora species. Tabling corals are fast-growing compared to other forms of Acropora, so that could explain why they are encrusting quicker (Stimson 1985).

KH01 – of the 47 surviving coral fragments, 43 have encrusted to some extent. A. digitifera has retained normal brown colouration, but A. hyacinthus and A. cytherea fragments have paled.

KH02 – 37 of 42 Galaxea fascicularis coral polyps have encrusted to the plate, across both colour morphs (pale brown polyps/brown tentacles, brown polyps/green tentacles). Many of the polyps have clumps of new, smaller polyps sharing the same coenosarc (the living tissue overlying the stony skeletal material of the coral), likely formed through budding from the original settled polyp (Davies 2017).

KH03 – 45 of 47 coral fragments have encrusted onto the plate. Fragments closer to light are encrusting faster, as seen in columns 2/3/6, where the calcified skeleton diminishes in size from top to bottom. Many of the fragments have paled, and the A. digitifera fragments are slow to encrust (maybe due to different lighting or orientation).

KH04 – 26 of 31 coral fragments have encrusted, 3 have fallen off, and 2 A.cytherea fragments have yet to encrust (perhaps due to less light availability compared to the other three columns).

Reefscapers mini coral frame Acropora digitifera - green huev

Mini coral frame of Acropora digitifera in our aquarium, displaying green hue

October 2019

At Kuda Huraa, we transplanted a total of 19 new coral frames, and our new coral/marine biologist, Sophie Plant, arrived on 11 October to begin her training in the Reefscapers coral program. Training included fieldwork protocol such as monitoring coral frames, how to clean frames, coral collections, and transplanting techniques. Database training was also given, including how to navigate QGIS and update the master Excel database. She has been brought up to speed for fieldwork and has already been transplanting with the coral team.

Our volunteers, Sorin Bridges and Martyna Socha, have been busy collecting, transplanting, cleaning frames, and recoating recycled frames during October. In total, we transplanted approximately 5,000 coral fragments during October; an increase of about 1000 fragments from last month. 70 frames were retransplanted at the Channel site; Montipora digitata is growing extremely well here.

Staff and volunteers also cleaned and prepared over 450 Water Villas frames, 150 Channel frames, and 66 House Reef frames, to be cleaned, recoated, and made into recycled frames for transplanting in the future.

The easternmost “arm” at the Starfish site has been suffering from sand accretion due to the changing direction of the ocean currents (east to west), and many coral fragments were buried. To solve this, we have been shifting all the Starfish structure’s 106 coral frames, and will soon be retransplanting with some new Pocillopora fragments.

Reefscapers coral propagation and reef regeneration Maldives

Coral Frame Transplantation and Monitoring

Our improved protocols on coral collection and storage techniques have resulted in lower rates of necrosis in our harvested coral fragments. Additionally, we will start to transplant Pocillopora fragments within 12 hours of collection, and we have installed a new water outflow system to provide greater inflow rates of fresh water. Acropora species remain healthier for longer, although some stress bleaching is often seen within the first few days after transplantation.

Experiment: Mortality Analysis

This month, we conducted a survey of Pocillopora and Acropora fragments, transplanted since the start of September, greater/less than 5cm in length. On the selected frames, over 1,000 coral fragments were classified as:

  • Alive (healthy, full colour),
  • Partially Bleached (paling, loss of colour on some areas),
  • Bleached (fully bleached from end to end),
  • Dead (covered in algae, total necrosis).

 Initially, we hypothesised that coral health would be better at the Water Villas site (compared to the Channel) due to the stronger ocean currents and better water flow (although too much water flow/energy can actually be detrimental to new fragments’ survival [Clark and Edwards, 1995]).

Our actual results show that coral health is very similar for both sites, so it seems as though any differences in water flow are not great enough to result in variations among newly transplanted fragment mortality. Results also showed consistently healthy corals within each site. Overall, Pocillopora seems to be healthier than Acropora, with healthy fragments of Pocillopora outnumbering healthy Acropora by 2 to 1.

Coral Plates in Aquarium-1 (plates KH01, KH02) and Aquarium-2 (plates KH03, KH04)

KH01 – the 37 remaining fragments have encrusted, and some Acropora cytherea fragments are beginning to meet one another. It will be interesting to see if they fuse together, or if they complete for the available space.

KH02 – the Galaxea fascicularis have undergone significant growth and budding from the original polyps, and the two colour morphs are also still present. Growth patterns seem to be upwards towards the light, however, the new polyps growing on the reverse side of the coral plate also suggest that G. fascicularis has a high resilience to low light conditions.

KH03 – 40 out of 47 fragments are encrusted, with fragments closer to the light sources continuing to encrust at a faster rate. Fragments at the top of the plate are beginning to encrust over the top, and there are indications of incipient axial corallites developing.

KH04 – 27 fragments are encrusted, and at a higher rate at the top of the plate. There is also paling on the top leading edges, which could indicate stress caused by high light intensity (directly beneath one of the aquarium’s lights). In general, Acropora hyacinthus continues to encrust at a faster rate than other species.

Reefscapers coral plate KH01 [KH 2019.10] [800]

Coral plate KH01

Reefscapers coral mortality survey [KH 2019.10] (2) [800]

Coral mortality survey – Channel site

Reefscapers coral plate KH03 [KH 2019.10] [800]

Coral plate KH03

Reefscapers coral mortality survey [KH 2019.10] (1) [800]

Coral mortality survey – Water Villas site

At Landaa, we transplanted 26 new frames this month. Our Reefscapers Special Volunteer Program has now come to an end, with a further 661 frames successfully recycled (cleaned and replenished) during October, bringing the final total to an impressive, target-beating 2044 frames. To gauge the success of the program, we surveyed 30 coral frames after 10-12 weeks, from both shallow (1-5m) and deeper sites (10-14m). The frames averaged a good survival rate of 84-90%, with 62-65% successfully encrusted coral fragments.

Coral Attachment Experiments

Rafia fibre – our experiments have ended, with most of the coral fragments failing to attach after 8 weeks; we found that the fibre covered too much coral tissue, causing local mortality.

Elastic “attaching gun” – after 7 weeks, good encrusting and survival rates with Acropora fragments, but Pocillopora fragments did not encrust at all. We will study this further.

New Coral Storage Tanks

Our 4 new fiberglass tanks were delivered this month, allowing us to increase the in-water storage capacity of corals and coral fragments. The tanks are being fed with sand-filtered water (to decrease sedimentation), each with individually adjustable inflow and drainage rates. They are installed on elevated concrete bases to improve the gravity-powered drainage and to prevent backwash at high tides. The standpipes in each tank are also elevated, to produce maximum water pressure. Two of the tanks have lids, and we have installed a permanent shade over the area (which also minimises leaf litter).

We will now be able to store many more coral fragments, separated by species if necessary, and for longer durations (currently increased from 2 days to 5 days, although we expect this to fall again during the warmer season March-April.) We have also successfully housed some of our clown fish brood stock and sea anemones in the tanks.

AI / Catamaran

We have ordered some replacement propeller parts, prepared a designated parking area on land, and will be working on a custom-designed trailer for transport to the ocean.

Our deep-learning model has now been trained on almost 400 coral frame photographs, comprising more than 6,000 individual pieces of coral, and is now relatively accurate at detecting and identifying corals. Next, we are using successive image processing algorithms to detect the metal bars, to then extract the shape of the frame for precise positioning of the corals on the structure.

[TOP] Healthy coral fragments encrusting onto the bars of our coral frames, photographed during the coral survey this month.
[BOTTOM] Our new coral storage tanks, with sand-filters and individually adjustable inflow.

Reefscapers transplanted coral fragments [LG 2019.10] (2) [800]
Reefscapers new outdoor coral propagation tanks Maldives (3) [800]
Reefscapers transplanted coral fragments [LG 2019.10] (3) [800]
Reefscapers new outdoor coral propagation tanks Maldives (2) [800]
Reefscapers transplanted coral fragments [LG 2019.10] (1) [800]
Reefscapers new outdoor coral propagation tanks Maldives (1) [800]

November 2019

At Kuda Huraa, a total of 18 new coral frames were sponsored this month, and overall, our coral team of staff and volunteers have transplanted 9,000 coral fragments in November (up 3,700 from October).

Our three-month volunteer program has been a huge success, thanks to the ‘Dynamic Duo’! From early September to the end of November, Sorin Bridges and Martyna Socha have helped to transplant 18,250 coral fragments! They have both been very valuable to the Reefscapers program, going above and beyond their duties in assisting our coral biologists and the wider Marine Savers team. A total of 477 frames were transplanted at the Water Villas site, plus a further 460 frames at the Channel were cleaned and readied for transplantation, plus an additional 80 old frames were recoated and repaired for future use. Congratulations, Sorin and Martyna, and thanks for all your hard work …  missing you already!

Tech Data Group

Last month, we were pleased to welcome 100 individuals from the Tech Data Group, who visited Marine Savers as part of a wider Kuda Huraa resort visit. Attendees were given a brief introduction to our Reefscapers coral propagation program, and then helped to transplant coral fragments onto their own sponsored coral frames. Later that evening, there was a turtle release event, including further discussion about our marine conservation efforts.

Coral Frame Transplantation and Monitoring

We have been continuing with our improved cleaning protocols (encompassing nets, collection tanks, buckets, gloves, tools) and our healthy coral fragments make the continued effort worthwhile. Pocillopora corals are harvested and transplanted the same day, and the increased water inflow of the new tank outflow system has helped lengthen the time for coral storage.

The Water Villas site is now finished, although some frames have suffered from build-up of Rhodophyta turf algae, which grows very quickly and can cover new coral fragments, blocking essential light. The algae seem to build-up to troubling levels in just 30-40 days, so we will continue to monitor and clean the frames each month to ensure the corals are not smothered.

At the Channel site, we have seen Chlorophyta algae growing on some of our frames, resulting in some coral tissue loss. Thankfully, these algae are much easier to remove than the Rhodophyta, and we will monitor and clean regularly.

At the House Reef, we have assessed coral growth and monitored the frames (cleaned, repaired, photographed). Sand is an issue for some frames, as the bottom bar is close to being buried by the shifting lagoon sands, smothering the lower coral fragments. Otherwise, much of the Acropora corals show healthy growth and they have responded well to the deeper water.

Mortality Analysis

For the mortality analysis this month, we focused on corals transplanted from early September onwards, looking for differences in survival of Pocillopora and Acropora fragments, greater than and less than 5 centimetres in length. A total of 600 fragments were classified as alive (healthy full colour), partially bleached (paling), bleached (white), or dead (covered in algae).

We were pleased to see that most fragments were healthy, and much improved on the bleaching we recorded last month. We assume that many of the partially bleached fragments have now recovered from the initial stressors of transplantation, which is a very positive sign. Results were quite similar between species, and at the two different sites, and we observed that the size of the transplanted fragment did not influence subsequent mortality.

Coral Plates in Aquarium-1 (plates KH01, KH02) and Aquarium-2 (plates KH03, KH04)

KH01Acropora digitifera and A. cytherea continue to grow well, with 2 A. cytherea fragments starting to fuse together. In contrast, the encrusting growth of the A. hyacinthus fragments appear to be forming a competitive ridge rather than fusing together. Additionally, where there is close contact between A. hyacinthus and A. digitifera, growth of the former is encroaching and winning over the latter.

KH02 – the Galaxea fascicularis coral polyps have continued to grow well, and now show budding from the original polyps. Polyps on the top side are larger and more numerous (more light) and show more budding at a faster rate, although polyps in much lower light on the reverse side are still growing well. New polyps have started to grow separately from the original polyps, suggesting they are able to spread and grow autonomously, not just from budding of the parent polyp.

KH03 – fragments closer to the light sources continue to encrust at a faster rate. The growth between A. hyacinthus and A. cytherea fragments appears to be forming a ridge (as KH01). Interestingly, A. valida has shown significant vertical growth and branching, with little encrusting onto the plate, whereas A. cytherea and A. hyacinthus fragments have encrusted well onto the plate but are showing little vertical growth.

KH04 – fragments continue to encrust faster at the top of the plate than the bottom, which is consistent across all the coral plates. There is also paling on the top of the leading edges, indicating stress caused by high light intensity. There is also evidence of bleaching on the underside of the fragments, suggesting they are not receiving enough light, and demonstrating that tabling corals appear to be very sensitive to light conditions.

Reefscapers coral plate Galaxea fascicularis

Galaxea fascicularis colonies fusing [coral plate KH02]

Reefscapers coral plate experiment

KH03: Growth towards light source (left);
A.valida fragments (top right);
A.hyacthinthus incipient axial corralite growth (bottom right).

Reefscapers Rhodophyta turf algae on coral frame

Rhodophyta turf algae on a coral frame

Reefscapers coral plate experiment

KH01: Ridge between A. cytherea and A. hyacinthus variant 1 (red);
A. hyacinthus > A. digitifera (yellow);
fusion between A.cytherea fragments (green).

Reefscapers Chlorophyta algae on coral frame

Close-up of Chlorophyta algae on the bars of a coral frame

At Landaa, 26 new coral frames were transplanted in November, and despite a decrease on the November 2018 figure, we have already beaten our annual target of 300 deployed frames, with the running total for 2019 now standing at 309 frames.

This month, we also mapped and monitored (cleaned, repaired and photographed) a total of 178 frames at the Water Villas, plus 100 frames at the ‘Blue Holes’ sites. We discovered some frames with lost/missing tags here, so for the first time, we plan to use monitoring pictures with our A.I. software to identify the correct tag numbers. If successful, this will save a large number of working hours, enabling us to quickly replace the tags, update G.I.S and upload the monitoring photos.
We have also installed 5 new ‘HOBO’ temperature loggers at the Blue Hole sites (at depths of 1-2m, 6-7m and 7-8m). We aim to closely monitor the health of the coral frames here, to determine if this site might be useful as a ‘refuge’ during the seasonal warmer months of March-April.

A.I. / Catamaran

Our catamaran is currently on stand-by as we are having quality problems with the propellers. We are in the process of replacing them and building a custom trolley to move it from the garage to the beach.

We are making good progress with the artificial intelligence. The aim is to identify which coral species are growing on the frames, just from auto-analysis of the monitoring pictures. This way we can identify frames which have lost their tags, and most importantly analyse coral survival and growth. There are several parts that need to be achieved for this to work:

  1. Coral detection: This is done by a deep learning framework, a convolutional neural network (CNN) that learns what coral fragments look like, from pictures that are manually annotated. We have had good results with this, and we continue to provide the network with new training pictures to widen the scope of successful situations. To date, we have analysed a total of 605 pictures with 9,442 annotations. The mean Average Precision is an encouraging 0.74-0.77, but this is highly dependent on the similarity between test pictures and training pictures.
  2. Frame detection: To know the position of coral fragments on the frame, we need an approximation of the 3D position of the frame, relative to the camera. We can detect the metal bars by merging the straight-line segments in the picture, to give the position of a few bars (we don’t know which ones) plus some false positives (rubble or other frames in the background). We then use a probabilistic method to try thousands of different camera angles and check how well the resulting pictures match the bars that we have detected. In the end, the algorithm proposes the most likely camera position it found. Once we know the camera position, we can calculate the proposed location of the whole frame on the picture. For now, we have an approximate 60% success rate.
  3. Combined information: Once we know the position of the frame and the corals on the picture, we can link them together. For each coral fragment that we detect, we can know which bar it is on, and its position on the bar. We can then merge the data from the 4 monitoring pictures to have a global description of the frame, specifically which coral fragments are present, with size, living state, taxonomic family and bar position.
Reefscapers coral frames GPS locations at Blue Hole

The ‘Blue Hole’ sites (West and East), showing the GPS positions of our Reefscapers coral frames

Coral Reproduction Pilot Study

This month, our new intern, Iris Van Djik, and our coral biologist, Simon, conducted a pilot study focused on the sexual reproduction of corals in our aquaria. The aim of this initial investigation will be to find the optimal method for the breeding of larvae from brooding corals.

There are two modes of sexual coral reproduction: broadcast spawning and brooding.

  • Broadcast spawners release their eggs and sperm in mass-spawning events once a year, governed by environmental factors such as lunar phase and temperature. The released gametes drift to the water surface where fertilisation takes place. After a few days, embryos will develop into planulae (coral larvae) and settlement will occur.
  • Brooding coral species have internal fertilisation and embryogenesis before releasing settlement-competent larvae. Brooders show extended reproductive seasons throughout the year, with some producing planulae almost year-round. In addition, they generally produce large larvae which already contain zooxanthellae (whereas the broadcast spawners uptake their zooxanthellae shortly after settlement). These factors make brooding corals an ideal subject for laboratory testing. Once released from the parent colony, planulae swim upward towards the light (positive photoaxis) entering the surface waters and being carried by the current. They will then use environmental cues (light) for habitat selection. Once the planulae settle, they metamorphose into polyps and form colonies through asexual reproduction.

Much less than 1% of coral larvae survive to see their first year. Reducing these early life-stage losses could result in a vast improvement of recruitment on the reef. This can be done by rearing the larvae in a controlled environment like aquaria. Therefore, the goals of this pilot study are to find the best methods for:

  • Collection of larvae from a coral colony.
  • Achieving best practice for settlement of coral larvae.
  • Achieving low mortality among settled planulae.

For the study, we used brooding corals of the genus Pocillopora. A colony of Pocillopora verrucosa of ±15 cm in diameter was collected from the reef at a depth of 3 metres. After careful removal from the substrate with the aid of a hammer and chisel, the whole colony was quickly transported to a continuous-flow aquarium. The aquarium was equipped with an air stone and Radion XR15w Pro lights, which mimic natural light patterns and the lunar cycle. Each morning and evening, and periodically through the day, the colony was monitored for release of planular larvae. Any planulae we spotted were transferred to a separate aquarium via pipette. We inserted ±250 sister planulae (same day cohort, released from a single mother colony) in this aquarium; these planulae were released 3 days before full moon.

Settlement substrate was available (bare coral rocks with CCA, crustose coralline algae). The flow was shut off to prevent planulae leaving the aquarium, however 75% water changes were made manually every day. We counted larval settlements in the first 4 days after their release, and found that 106 planulae had settled on the substrate. Most of the settlers had finished their metamorphosis into a primary polyp. After 7 days, the primary coral polyps were first observed feeding on rotifers, and they had also started budding (asexual growth).

The next step in this pilot study will be to achieve low mortality among the primary polyps, by creating a healthy environment. The rapid growth of algae in the aquaria has proven to be a challenge, so we plan to introduce grazing marine species in the future. Moreover, we want to get an indication of when planulae releases peak, according to the lunar cycle.

Irene's internship coral research Maldives
Reefscapers coral reproduction study

December 2019

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