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.

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