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
Coral frames at the Channel site (before relocation work)
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.