Monthly report updates from our Reefscapers coral biologists at Kuda Huraa and Landaa Guraavaru.
You may also be interested in our extensive report on Coral Bleaching (2016), last year’s Reefscapers Diary (2017), and the public gallery Coral Frame Collection to view photographs of your own sponsored coral frame as part of our Reefscapers coral propagation project.
During January, at Landaa Giraavaru we made 33 new coral propagation frames and recycled a further 50 frames, and at Kuda Huraa we made 16 new frames. We continue to line the Water Villa walkways with our small-sized frames, and hope to attract herbivorous grazing fish to the area to control algal growth by extending outwards towards the natural reef. We are siting larger frames along the boat channel at approximately 9m depth, close to large healthy colonies of Acropora species.
A storm at the start of the month displaced and even flipped some of our coral frames, so we righted these frames and verified their GPS mapping coordinates. We also noticed some juvenile Pocillopora coral colonies were showing signs of bleaching (on our frames and the natural reef), although no Drupella snails were seen.
Acropora coral colonies from the reef crest remain our go-to source for new propagation fragments, with new coral growth seen to quickly encrust the frame and cable tie (more successfully than Pocillopora fragments).
Our Junior Marine Savers busy attaching coral fragments to a frame
In order to test whether or not fragments with multiple breaks can survive, two small coral frames were created. Photos were taken of each side of the frame, so the fragments can be seen clearly; we hope to gain a better understanding of the survival and growth rates of different coral fragments.
We regularly maintain our coral frames – replacing dead or missing coral fragments, removing any algae, and taking reference photos from each of the 4 sides (to study survival rates and growth patterns, and to email to our coral frame sponsors).
During February, we transplanted 17 new coral frames at Kuda Huraa and 35 at Landaa Giraavaru. Many old frames have also been ‘recycled’ (replenished with new coral fragments), and we have been targeting the frames found across our popular snorkelling sites. We have also finished relocating vulnerable frames to a harder rubble substrate to minimise sand accretion and protect the lower bars (with rocks under the feet of some large frames).
During the past 12 months, one of our primary goals has been to diversify the sites where we deploy our coral frames, to increase resilience towards future bleaching events. Some of the variety of locations include:
- “Blue Holes” (5m deep) from sand dredging.
- 25m depths (staff beach).
- Shaded along the Water Villa Pathway, to receive lower levels of direct sunlight.
- “Coral Bommies” (separated from the natural reef by large sand patches), featuring large healthy wild colonies of Acropora and bouldering corals at depths of 9m.
Predation Recovery Experiment
A large colony of Acropora pulchra under attack from Drupella snails was identified and collected from the wild reef. We divided and transplanted the coral fragments onto a single test frame, and plan to take twice-weekly photographs to monitor how individual fragments recover from predation.
All current drone photographs for Kuda Huraa and Landaa Giraavaru have been successfully mapped with consistent and reproducible Ground Control Points (GCPs) for accurate alignment with future photographs. The image maps will enable detailed comparisons of the marine landscape over time (corals, sand movement, seagrass coverage). For example:
– areas of wild coral coverage (Montipora digitata and Porites cylindrica) on the easterly reef flats can be monitored for future growth or recession,
– the natural movement of sand around our Spa Island has already been revealed (which can help in siting future coral frames). The animation below shows 3 images in sequence from May 2017, Nov 2017 and Feb 2018.
3D generated image
3D generated image
3D generated image
Ground control points (GCPs)
This month at Landaa Giraavaru, we transplanted 25 new coral propagation frames (and recycled 10 old frames), and at Kuda Huraa we deployed a total of 18 new frames. We have been relocating our coral frames around Landaa’s Water Villa site, to create an unbroken chain of frames to encourage the movement of herbivorous fish to graze and remove any algae. The coral frames here are very healthy due to the plentiful shade from the over-water villas (reduced stress from the sun’s heat/UV rays). We have also been seeing more Acropora species recruits around this area.
The jetty pillar frames have been recycled (with mostly Acropora and some Pocillopora coral fragments) and we will closely monitor them for survival and mortality. Some fish predation has recently been observed in the house reef, so we are trialling transplantation of Acropora (and possibly Pocillopora) coral species to monitor potential predation.
Predation Recovery Test Frame
Last month, a large colony of Acropora pulchra that was being eaten by Drupella snails was transplanted onto a single frame. Fragments with scars were monitored for tissue loss or growth along the scar. In most cases, we observed no change or some overgrowth by algae. If the fragments overcome the initial bleaching, they may be able to overcome the algal growth and begin growing tissue over the scarred area.
NOAA has placed the Maldives at Alert Level 1 (from 3 April), with a 60% chance of bleaching in the first week of May due to seasonally warm ocean temperatures. If bleaching does occur as predicted, it will hopefully only last three weeks, and corals should be able to recover as the waters start to cool again. We will be closely monitoring our coral frames during this period, particularly at the Water Villas site where vulnerable frames can be moved into the shade under the board walks at the first sign of bleaching.
We recently attended a coral-line workshop, organised by Clare Baranowski and Emma Bell, resident marine biologists from Gili Lankanfushi. In attendance were marine biologists from resorts and projects around the Maldives including Bandos, Atoll Volunteers and Manta Trust. The aim of the workshop was to learn about the process and benefits of the coral-line methodology.
The coral line-method uses rope attached to a frame (frames are 2x3x5m, 5m lines) with coral fragments twisted into the rope at 5cm intervals to support 100 fragments per line. Since the programme started, large colonies have grown and the resultant heavy lines were moved to hang on the edge of the frame. As all the lines are in the same area, they are easily monitored and maintained, to provide stock for fragmenting. Predatory crown of thorns starfish are not able access the suspended corals, and a nearby sand patch prevents Drupella snails from reaching the nursery. Algal growth is removed from the lines simply by shaking them.
During the 2016 El Nino event, an impressive 68% of the corals on the Gili lines survived, higher than seen for both local reefs and other coral regeneration projects; the specific reasons for this comparative success remains unclear. The lines are located on the western side of the island at 6m depth on a sandy area exposed to minimal predation. Perhaps the exposure to local currents was a factor, or the high position of the ropes in the water column.
However, despite the success of the coral-lines, out-planting the growing coral colonies has been more challenging. Corals are transplanted to the same depth (using epoxy putty on bare reef-rock substrate), but often suffer from heavy fish predation as the surrounding natural reef is otherwise devoid of living coral. This is where the use of Reefscapers coral frames is more successful, being a single step process with no out-planting, the frames quickly establish to become part of the reef. As the primary goal of any coral propagation programme is to repopulate natural reefs, this is probably the largest downfall with the programme. However, the resilience of the coral-lines to bleaching effects cannot be ignored, so maybe a combination of propagation techniques, using both lines and frames, could yield better long-term results. Practically, lines could provide additional coral nurseries for fragment harvesting, to better withstand future bleaching events.
At Landaa Giraavaru, we made a total of 29 new coral frames, monitored 250 frames (repaired, cleaned, photographed) and removed 70 frames from Parrot Reef for recycling (re-transplanting with healthy coral fragments, following bleaching).
Pocillopora coral species has been the primary coral deployed due to its relative abundance. Acropora species are growing well on our frames at the Water Villas site, and colonies have even been observed growing on the jetty columns. We have installed structural bracing to our coral storage tank, allowing larger volumes of corals to be collected and stored for longer periods, aiding our frame recycling efforts.
The seasonally warm ocean temperatures have reached 31°C in the lagoon, increasing the temperatures in our large 3000L aquarium, which cycles fresh water directly from the sea. We have seen increased growth of filamentous algae, mainly at the top of the aquarium where the light is brighter, and we are closely monitoring our corals.
This month, we have started to repair and replenish the House Reef site with coral fragments of Acropora, Monitpora digitata and Porites cylindrica, and will be monitoring for predation from corallivores. Whilst diving in pairs, we lifted more than 40 dead frames onto our boat using rope hoists. These frames will be recoated with sand-resin mixture before recycling.
Fish predation continues to be an issue on the house reef. We recently observed a black-spotted pufferfish feeding on the branch tips of multiple Acropora species, although it’s unlikely that this fish species is responsible for the complete consumption of coral fragments we have witnessed on our Christmas tree frame and other parts of the house reef. So far, there are no signs of predation on Montipora and Porites corals, so we will increase their deployment alongside Acropora and Pocillipora species to ensure that some fragments survive predation stress.
This month, we removed over 40 crown of thorns (COT) from the Channel area, mainly from the wild coral colonies. These patches of wild Montipora corals in the lagoon seem to act as a buffer zone for the main channel site in terms of COT and Drupella predation.
Some Acropora coral paling was seen towards the end of April, so we relocated the most affected frames to the shade of the water villa boardwalk. A few fragments are fully bleached, and we will continue to monitor closely during these warmest few weeks of the year.
Black-spotted pufferfish (Arothron nigropunctatus)
Signs of pufferfish predation on Acropora tenuis
Coral plate (January)
Coral plate (April)
At Landaa Giraavaru, we transplanted 23 new coral frames and monitored 260 frames across our Parrot Reef, Coral Trail and Water Villa sites (this involved cleaning, photographing and updating QGIS satellite data). Our recycling work of old frames is also continuing at both Parrot Reef and Coral Garden. Very large mature frames are too heavy to relocate, but their coral skeletons provide a valuable habitat for marine life, so we are filling any empty bars with new coral fragments.
We have been developing our Marine Biologist Course for the Four Seasons Apprenticeship Programme, and have expanded the coral propagation component this month. We cover coral reef ecosystems and summarise our Reefscapers coral restoration project. We also outline coral structure and identification, and discuss threats to coral reefs. This is followed by ‘Build A Reef’, where the apprentices get hands-on with our coral biologist, transplanting their own coral frame. Field work involves placing and photographing the new frame out in the lagoon, and updating our coral frame database with the QGIS satellite location and new photos. Apprentices Hulaam and Saaniu have both completed our coral training, and are progressing well at our Marine Discovery Centre.
New coral fragments added to old frames
We were lucky to see one of the mushroom coral specimens in our aquarium in the act of spawning, as it started to excrete a fluorescent orange slime. We collected a sample and examined what we think are eggs under the microscope.
We have taken some time out this month to help staff at fellow resort ‘Club Med’ with their own Reefscapers programme, after being without an onsite marine biologist for some time. Club Med staff came to visit our Centre at Kuda Huraa, and then we went to visit their current setup. Interestingly, they have many healthy Pocillipora colonies growing on frames out in the lagoon, and in a good location (rocky substrate, strong current, close to the jetty). We visited the reef crest with the new onsite marine biologist, to harvest some Acropora coral fragments for propagation and transplanting onto empty frames.
Bleached coral fragments – Acropora puchra & Acropora digitifera
This month, we transplanted 13 new coral frames at Kuda Huraa, and 35 new frames at Landaa Giraavaru (mainly at the Water Villas site). In addition, our intensive recycling efforts have seen 3600 coral fragments added to existing frames at Coral Garden (LG) and a further 3000 fragments at the Channel site (KH).
We completed the geometric pattern at the Water Villas (KH); the old frames had a mixture of species (Montipora digitata, M.foliosa, Heliopora coerulea, Acropora sp.) but we transplanted each new frame with a single species to prevent competition (Acropora tenuis, A. digitifera, A. hyacinthus, A. millipora). We placed 15 frames on the House Reef (KH) to reintroduce Acropora species, although they were heavily predated upon and many fragments soon died. We will continue to try and overcome predation with more Acropora and other species (Pocillipora sp., Porites cylindrica and Montipora digitate).
We are pleased to see that natural recruitment of Acropora species is continuing to take hold around the lagoon, and where colony sizes allow this provides a useful source of new fragments for propagation.
Plot of the geometric patterned coral frames
Redfin butterfly fish eating Acropora coral fragments
Geometric patterned coral frames in the lagoon
grazed Acropora coral fragment
Is Algal Growth Correlated to Coral Frame Placement?
by Tiana Wu
Algae can be a problem on our coral frames, potentially overgrowing and killing live coral tissue (Jompa and McCook 2003). If frames are isolated from each other and from the natural reef, they are less likely to be grazed upon by algae-eating herbivorous fish so more likely to suffer from excess algal growth (Cramer et al 2017).
Existing coral frame monitoring photographs were selected from Landaa Giraavaru’s water villa area (a site with frames in both orderly rows and in isolated groups). Monitoring photos were assigned a value from 0 to 5 to represent the percentage of algal coverage (0-20-40-60-80-100%, Barott et al 2012), before mapping their locations to prevent bias. All the monitoring photos were assigned algae scores by Tiana herself, to prevent discrepancy between scores. The age of coral frame was also included in the dataset, to analyse coverage over time (0-6-12-18-24 months). The data set was then mapped using QGIS (QGIS Development Team 2018) to generate a map that displays all the frames with their corresponding algae score.
The youngest frames showed the least algal growth as expected but increasing age did not always result in greater algal coverage, suggesting a possible correlation with placement of the coral frame. Frames located at the outer edges of the rows tended to have more algae than frames towards the centre, suggesting coral frame placement might play a role in the accumulation of algae (perhaps the central clustered frames are easier to find and thus more grazed upon). The results are inconclusive and further studies are required.
- a relatively small sample of coral frames.
- algae scores were given by visual estimation (not precisely measured or computerised).
- the quality and clarity of the monitoring photos was variable (taken as they are by different staff under different environmental conditions over periods of several years).
- the effects of shade on the growth of algae.
- increased numbers of coral frames, of various ages across multiple locations.
- Barott KL, Williams GJ, Vermeij MJA, Harris J, Smith JE, Rohwer FL, Sandin SA.2012. Natural history of coral-algae competition across a gradient of human activity in the Linne Islands. Mar Ecol Prog Ser. 460: 1-12
- Cramer KL, O’Dea A, Clar TR, Zhao J, Norris RD. 2017. Prehistorical and historical declines in Caribbean coral reef accretion rates driven by loss of parrotfish. Ncomms. DOI: 10.1038/ncomms14160
- Jompa J, McCook LJ. 2003. Coral-algal competition: Macroalgae with different properties have different effects on corals. Mar Ecol Prog Ser. 258: 87-95
- Python Software Foundation. 2018. Python Language Reference, version 3.6.5. http://www.python.org
- QGIS Development Team. 2018. QGIS Geographic Information System. Open Source Geospatial Foundation Project. http://qgis.osgeo.org
- Smith JE, Shaw M, Edwards RA, Obura D, Pantos O, Smriga S, Hatay M, Rohwer FL. 2006. Indirect effects of algae on coral: algae-medicated, microbe-induced coral mortality. Ecology Letters. 9: 835-845.
A construction team from ‘Solar Swim’ was on site this month (LG), to complete preliminary work on a solar panel installation. We have started a shading experiment, harvesting Acropora coral fragments from the colonies found attached to our existing floating solar panels (at the Staff Beach) to transplant onto two small frames. One frame was located directly under the solar panels in permanent shade (5m deep); the second frame was placed at the Water Villas. After just 20 days, the shaded frame is already displaying better growth and attachment than its counterpart. The frames will be monitored regularly.
We retrieved our temperature loggers from the lagoon (KH) this month, to analyse the latest readings. Like our findings in 2017 (April to August), the temperatures of the Channel (28.9°C) and House Reef (29.0°C) were very similar, but with more daily fluctuations in the Channel. From our data, it seems the ocean temperatures this year have been slightly cooler than in 2017.
We recently removed around 40 of the corallivorous Crown of Thorns starfish (COTS), mainly from patches of Montipora digitata species at our Channel site (KH). The COTS remain well hidden during the day, so we plan night snorkel trips to better find them. We think the COTS are arriving via the small channel between the islands of Kuda and Bodu Huraa, as we sometimes spot them in sandy areas free from corals. This may explain how the COTS are quickly able to repopulate an area after removal, so we will be expanding the area of our night snorkels in future.
Acropora fragment after 3 weeks, with new corallites and increased calcification (experimental coral frame in our marine aquarium, Kuda Huraa)
Underwater temperature loggers data plot, Kuda Huraa
Transporting our coral frames by buggy
Crown of Thorns – possible route around Kuda Huraa
Frames at the Water Villas continue to grow very well, and we have started to take small fragments to spread the coral on the same frame (directly next to the mother colony where possible). Shaded frames under the boardwalk were moved into the sun, as coral growth was slow due to the spread of algae.
We witnessed an unusual phenomenon for the first time this month, with many of the 2,000 new Channel fragments dying off within a week. This was strange, as there were only minimal signs of predation (impacted tissue and corallite damage), and we had been following our normal protocols for fragment collection and transplantation.
When we noticed the die-off on several new frames deployed on the other side of the island, we suspected possible contamination. All gloves, buckets and collection/storage equipment were immediately and thoroughly washed and bleached. Currently, this problem seems to have subsided, and all new frames are being closely monitored.
Acropora fragment July [top] and August
Mysterious mortality on coral frame
Mysterious mortality – coral fragment closeup
A new Acropora coral plate was made this month. Steel epoxy putty was used to plug small coral fragments of various species into the plate holes:
- Acropora millepora (AMP),
- A.tenuis (ATE),
- A.cytheria (ACY),
- A.hyacinthus (AHY).
Each column on the plate consists of a single colony except for AMP, where the same colony was used for two columns. This was done so the effect of light exposure (decreasing with depth) can be observed without the influence of genetic variation within species. Fragments located at the top of the plate have the highest light exposure and seem to be in the best health following initial placement.
After sixteen days:
- 29% of fragments are alive but display some tissue necrosis (mostly at the base of the fragment, possibly a reaction to the epoxy putty). These fragments will be closely monitored to see if they are able to recover.
- 25% have died, mainly rows 4-7 of ACY and AHY (possible contaminant or placement error).
- 18% show small amounts of growth and encrusting.
- The remaining 28% of fragments appear healthy but are yet to start growing.
[L] healthy; [R] base necrosis
We have been attempting to replicate a video posted by Melissa Roth “Coral Bleaching Time-Lapse in White and Fluorescent Light” to study the physical changes that occur in corals during the bleaching process. Specifically, a bubble seems to form within the coral that seems to cause bleaching and death. We are using a webcam and magnifying glass for close-up filming, and have been experimenting with different methods of heating the water.
This month we caught the process on camera for the first time! It took 12 days for the fragment to bleach, at an average water temperature of 32°C (24hr light, no water changes, water level adjusted to compensate for evaporation). Whilst there was no recorded “bubble release” as expected, the footage did show some interesting behaviour.
We can see the final stages of bleaching and loss of tissue (occurring over an 8-hour period) with particulate matter being forcefully ejected from the fragment (highlighted in red). We are unsure what this could be, and have so far been unable to find similar events described in the literature (any opinions greatly received … drop us a line!).
Online video shows Heliofungia actiniformis forcefully ejecting its symbiodinium zooxanthellae after just a few hours at 32°C; however, in our experiment the phenomenon was seen after several days and after the fragment had already lost polyp motility (and was exhibiting tissue sloughing). We think that our video does not show the expulsion of zooxanthellae, but some other phenomenon.
We hope to repeat the experiment again, using a different coral species, and a reduced video frame rate (for easier data transfer and editing).