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.
Children enrolled in our Junior Marine Savers helping with Reefscapers coral propagation projects
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.
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).
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).
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
Acropora tenuis (bottom) overgrowing Acropora millepora (top)
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.
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 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).
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.
Aerial shot of Reefscapers coral frames, arranged in a geometric pattern at Kuda Huraa water villas
Growth of macro-algae
Heavily-predated coral fragment
Coral plate in Feb (left) and March (right), showing competition between Acropora millepora (top of each photo) and Acropora tenuis (bottom).
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.
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.
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Coral spawning! You see all those little orange dots? They are actually coral gametes that are just about ready to be released from the coral species Acropora hyacinthus. With the full moon they release their gametes into the water to be taken by the tides. Hopefully they will form baby corals (planulae) and will be the next generation of reefs. It is hoped that they have the heat resistant genes to survive the warming ocean. 🌏🌞🌊🐠💙 . . . . #coral #coralreef #chasingcoral #coralspawning #climatechange #maldives #oceanlove #tropical #staysalty #blueplanet #oceans #marinelife #natgeo #natgeomv #polyp #marineconservation #marinebiology #microbiology #reefscapers #fsmaldives #fskudahuraa #marinescience #marinebiologist #conservation #conservationist
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.
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).
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.
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.
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.
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 ourcampaign to expand the development and research for our pioneering robotic catamaran project.
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.
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).
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.
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).
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.
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.
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).
Coral bleaching mortality by species 2019
Digital GIS mapping of our coral frames at Landaa Giraavaru