Monthly report updates from our Reefscapers coral biologists at Kuda Huraa and Landaa Guraavaru.
You may also be interested in our Coral Bleaching (2016) report, and the Coral Frame Collection to view the latest photographs of your own sponsored coral frame as part of our Reefscapers coral propagation project.
31 new coral frames and 65 recycled frames were transplanted at Landaa Giraavaru during January. 36 of the frames were located in our new ‘Water-Villa-300’ site, and 60 frames at the ‘Parrot Reef’ site (which now totals 458 frames). We only used Pocillopora species as healthy Acropora species are still rare and live mostly beyond 12m deep.
At Kuda Huraa, 9 sponsored frames and 13 recycled frames were placed in the Channel site during January.
Coral Growth Study
To closely study coral growth, we have placed new coral micro-fragments on Perspex sheets in an aquarium, where conditions are optimal and observations can be made regularly. So far, the coral fragments are showing good health overall. Holes were drilled in the Perspex sheets and fragments were sized accordingly (so we do not use glue or fixative substances that could impact the experiment). Several species have been used on the two sheets including encrusting, massive and digitate corals.
Coral mounted on Perspex sheets in our aquarium
Closeup of the mounted coral micro-fragments
At Landaa Giraavaru, 31 new frames were transplanted during February, at our new ‘Water Villa 300’ site. Fragments of Pocillopora species continue to be the only type of coral that we use, as healthy Acropora species are still rare and live mostly beyond 12 metres deep.
At Kuda Huraa, 19 new coral frames were made and a further 31 frames were recycled and deployed in our Channel area. Frames continue to show good health and have not been affected by predation. Frames that were transplanted with Acropora coral fragments have been doing very well; the colonies are growing nicely and now cover the cable tie that was used to attach them to the frame. Pocillopora coral fragments are healthy but are not growing as quickly. Efforts will be made to collect more Acropora colonies from the reef off Girifushi (Military Island) as they are showing to be more successful on our frames.
Recycled coral frames at Kuda Huraa’s ‘Channel’ site
Coral growth study
The coral micro-fragments have been showing good progress, and the skeleton of some fragments have started covering the Perspex sheet. We have been using a program called Pix4D to render 3D images, to closely observe and study the patterns of growth.
Our Coral Taxonomy Project is still ongoing during 2017.
38 new frames were transplanted at Landaa Giraavaru during March, using fragments of Pocillopora corals as large Acropora species have not been found at shallow depths. Juvenile Acropora colonies are starting to appear near our new ‘Blu Reef’ site. These colonies are budding from deceased colonies built upon the old square frames. Monitoring has begun on five of the small colonies to track growth and to observe whether bleaching occurs during the warmer months.
Acropora baseline study
At Kuda Huraa, we transplanted 16 new coral frames during March, and re-transplanted (recycled) 36 frames at our ‘Channel’ site using Pocillopora fragments collected from the reef flat off Girifushi. All frames in the Channel have been placed in parallel lines, to exploit the sand substrate as efficiently as possible by placing many frames within a small area. Frame monitoring will be easier, and the site will become an interesting feature for snorkellers.
We have 26 frames at the House Reef site deployed since the 2016 bleaching event. Surviving Acropora colonies on deeper frames (10m) were fragmented and replaced on old frames (recycling) to expand our strategically placed ‘nursery’ with better resilience against a future bleaching event.
The overall health of the House Reef has been decreasing, with digitate coral species becoming scarce, making coral collection for our frames more difficult. Most remaining Pocillopora colonies are diseased and partly covered in algae, making our Reefscapers work more important as colonies must be collected and propagated to reduce disease mortality. Species of ‘massive corals’ are showing scars from parrot fish feeding, and suffer from crown of thorns predation.
Coral growth study – 3 months
The corals on one Perspex sheet spent several hours out of water due to a pump malfunction, causing most of the micro-fragments to die. The Perspex sheet was bleached and photographed to show fragment growth at two months. The second Perspex sheet has done well and is still growing in our tank.
Drupella snails are a further pressure on corals, and feed in large numbers on the living tissues of diseased corals in particular. It is unknown whether the Drupella or the disease appears first – do the snails act as a disease vector or do the feeding scars later become infected? Or the Drupella may simply prefer to feed on the already-diseased corals.
We plan to study Drupella feeding preferences under controlled conditions by providing three coral feeding options: healthy, diseased, scarred. Our preliminary study compared healthy/diseased corals, with the snails seeming to prefer feeding on the diseased coral fragments. If this feeding preference is confirmed in our further trials, the threat of Drupella acting as a serious vector of disease would be minimal, and conservation efforts could be focused elsewhere.
Reefscapers experiments with coral micro-fragments
(click to enlarge)
Drupella snails feeding on diseased coral
coral frames in the Channel site (Kuda Huraa)
As the El Nino events persist around the world, we are seeing the effects on our corals in the Maldives. Elevated temperatures (up to 30 degrees Celsius) recorded on nearby reefs have caused some colonies to lose colouration. As we enter the warmest period of the year (April into May), careful monitoring has begun at each of our coral frame sites. This year is not predicted to be as catastrophic as last year’s bleaching event, however, we have already witnessed stressed corals of all sizes, with some bleaching on our coral frames and the smaller wild reef colonies. Although temperatures are not as high as those seen in 2016, we have observed bleaching in some areas, with natural Pocillopora colonies losing some colouration. Pocillopora fragments on our frames and the few surviving wild Acropora colonies have also been getting paler.
At Landaa Giraavaru, a total of 33 new coral frames were placed into the water during April, located at our ‘Blu Reef’ and ‘Water Villa 300’ sites. Once again, Pocillopora species were generally used, as they are the most predominant of the branching corals on our reef. Some Acropora were placed on frames when broken fragments were found.
To mitigate the effects of the warming ocean temperatures, we have been working to relocate some coral frames exhibiting stress. To test the resilience of our corals, frames were moved to shaded areas, deeper areas or left in place. The primary goal is to restore the reefs without needing to relocate vulnerable frames each time the ocean temperatures start to rise. We hope to find some coral genotypes that are naturally more resilient to the warmer waters.
At Kuda Huraa, 12 new coral frames were transplanted during April. We have also been busy relocating a total of 108 existing frames from shallower waters at the Channel site to cooler waters on our House Reef (at depths of 10 to 13m). The area we chose has a sandy substrate and healthy colonies of Acropora and Pocillopora nearby. 40 frames will remain in our Channel to act as a scientific control group for the experiment. Stacks of 5 frames were deployed using a lift-bag that acts as a ‘parachute’ to ensure the frames land the correct way up. We then removed the lift-bag by freediving rather than scuba diving, as this was faster and more efficient.
Further afield, we observed healthy coral cover on some wild reefs in Rasdhoo Atoll. Acropora recruits were found on reef flats at depths of just 50cm, with mature Acropora colonies at 5m. As we might expect, exposed sites on the outskirts of the atolls present the best cover of healthy corals.
May has brought some cloudy weather and seasonal monsoon rain, cooling the ocean temperatures and allowing any temporarily paled coral colonies to recover. During the month, we transplanted 10 new frames at Kuda Huraa and 14 at Landaa Giraavaru.
Currently, Landaa Giravaaru has 3,200 coral frames deployed in its waters; 2,500 of these will no longer be monitored as they are diseased or bleached following last year’s coral bleaching event. These frames still provide an important ecosystem for a myriad of marine life, so many with surviving colonies are being ‘recycled’ by removing dead corals and replacing them with new living fragments. To keep pressure off the natural reefs, all new fragments will be harvested exclusively from our frames, and we are photographing our work to discover which species work best as donors.
We have also observed many bouldering corals recruiting naturally to a cement block, attached to a buoy (photos below). So we have started to deploy some overgrown frames in this area of the lagoon, to add additional viable surface area for the recruits to attach.
Diseased Colony Experiment
We wanted to determine the best strategy for any diseased coral colonies, particularly as the warmer bleaching season approaches. We selected ten part-diseased colonies from our House Reef to photograph and tag for monitoring. These will be compared with ten part-diseased colonies that were fragmented and placed on recycled frames (at 8m depth). We will monitor progress and growth over the next few months, to see if fragmenting the partially diseased colonies turns out to be beneficial or detrimental.
We have started to map the island of Kuda Huraa and the surrounding lagoon by using drone imagery. Overlapping images taken with an aerial drone were merged and processed in PIX4D mapper to generate a high resolution geo-referenced image with specific GCPs (Ground Control Points). A GCP is a specific point (such as the end of the jetty) given accurate geographic coordinates (and altitude) using Google Earth.
This year, the ocean temperatures did not reach the deadly highs of 2016, however, we have seen stressed corals at each of our sites. To mitigate the effects of warmer ocean temperatures, we have been moving some frames to deeper areas at the Parrot Reef and Blu Beach sites, and to locations underneath the over-water villas. The coral fragments on these shaded frames currently have darker algae, and seem to be growing at a faster rate compared to adjacent frames exposed to partial or full sun. We will continue to monitor these frames closely.
During the month of June, we transplanted 30 new coral frames into the lagoons at Kuda Huraa and Landaa Giraavaru. We have also been busy recycling our older frames (following the recent coral bleaching events) and returning mechanically damaged frames to the local island of Fulhadhoo for refurbishment. We have also started to use a kayak for transporting frames around the shallower parts of the lagoon.
Diseased Colony Experiment
Out of 263 diseased fragments, only 4 have so far died (98% survival rate); this is higher than the standard fragment survival rate on our frames, perhaps because the fragments were transplanted during dives and were never exposed to the air.
Parrot Reef Re-Mapping Project
In June, we started a large project to remap and sort our Parrot Reef site. Through 5 dives, we rearranged all 400+ frames of Parrot Reef into straight lines, and then pinpointed their locations using QGIS geographical software. In the future, deploying frames in a linear fashion will become the standard, especially at large scale, enabling clear and concise mapping.
Reefscapers coral frames – under a water villa (left), open lagoon (right)
During July, 12 new coral frames were transplanted at Kuda Huraa and 31 at Landaa Giraavaru.
At Kuda Huraa, 32 old frames were recycled from the Starfish and Turtle sites and deployed in our Channel area; these are the frames that suffered during the recent coral bleaching event and have now been given a new lease of life. We have also transplanted new Pocillopora coral fragments onto some old frames at the Water Villa site, that had become a shelter for a variety of fish. We expect the corals to grow well here, as they are shaded by the jetty and exposed to strong currents.
At Landaa Giraavaru, we have monitored (cleaned, maintained, photographed) a total of 108 frames at the Parrot Reef and Landaa Water Villa sites. We will be designating specific areas of frames for monitoring every six months (rather than individual scattered frames), to facilitate easier and more efficient monitoring. Our coral frames at the Water Villas site were much healthier, with higher fragment growth rates and less mortality compared to the Parrot Reef frames. Frames that were found with dead fragments were recycled during the dives from nearby healthy colonies; the dead fragments were not removed to preserve the 3D complexity of the marine ecosystem.
What Is Coral Bleaching?
Coral bleaching is caused when the water temperature increases beyond a certain threshold, and can result in coral mortality if this temperature threshold remains exceeded for a relatively prolonged period of time. The symbiotic algae (zooxanthellae) that provide energy to the corals through the reaction of photosynthesis produce lethal levels of oxygen as the reaction speed is increased by the warm water temperatures. The quantity of light in the environment equally effects the production of oxygen, the latter increasing proportionally to the amount of light provided. Bleaching is a process during which corals expel the symbiotic algae to reduce the amount of oxygen produced.
In April this year, several colonies of Pocillopora showed signs of bleaching through lack of colour. This was alarming as 2016 was a year of widespread mass bleaching. In order to prevent bleaching on our coral frames a second year in a row, more than one hundred frames were relocated to deeper waters on our house reef, a cooler site with less light (so reduced risk of bleaching). Fortunately, the monsoon cloud and rain came early enough this year to interrupt the bleaching in the Channel area by lowering the water temperatures.
CoralWatch – recovery colour monitoring
Thirty frames were randomly chosen from both our Channel and House Reef sites at Kuda Huraa. Each fragment on these thirty frames was compared to a standardised colour chart to assess the recovery status in a standardised manner. This process equated to more than 600 monitored coral fragments per site. Each fragment was placed in a colour category ranging from one to six; category one corresponding to a completely bleached fragment (almost no zooxanthellae) and category six to a very dark fragment (large quantity of zooxanthellae).
The number of bleached fragments was found to be low at 1-2% across both sites, meaning most of the corals had recovered successfully (symbiotic algae had returned). However, the number of fragments remaining pale was found to be greater in the Channel (54%) than the House Reef (18%), possibly due to lower light and temperature levels at greater depths (average 3m deep at the Channel, compared to 12m at the House Reef).
Outreach with Kendhoo
We recently partnered with The Manta Trust to participate in their educational outreach program at the local island of Kendhoo. The team created an educational presentation aimed at educating the local students on the impact the coral reef has on their daily life, as well as how they can best protect it. After the short presentation and informational handout, everyone participated in a Coral Reef ‘Jenga’, a game designed to increase awareness of the positive and negative interactions affecting reefs and the ‘collapse’ of an ecosystem. The schoolchildren thoroughly enjoyed the game and seemed to take away a lot from it.
After the fun and games, we headed to the ocean for a brief snorkel on the house reef. As seems to be the norm throughout the atoll, large bouldering corals and some Pocillopora were present; on closer inspection, recruits of Acropora, Galaxea and other less common recruits were found in high numbers. We pointed out some of the various coral species, as well as any diseased and bleached corals we encountered, encouraging the children to continue visiting their reef and look for changes in the coral cover.
Sea Surface Temperature Monitoring
To further understand the impact of water temperatures at our different sites around Kuda Huraa, temperature loggers were placed in both the Channel and House Reef. The data recorded shows the daily variations of temperature in the shallower Channel area are greater (1.9◦C variation) than at the deeper House Reef site (0.8◦C variation) as might be expected. More surprisingly, the average daily temperature of the two sites was found to be identical, explained by the low temperatures observed in the Channel overnight.
It is likely that these variations in temperature at the Channel site are what have stressed the corals, causing paling and bleaching. Furthermore, corals on the House Reef (at 12m) bleach later in the year than Channel corals (at 3m) and are therefore more likely to be “saved” by the arrival of the monsoon.