Healthy Acropora growing on our frames, photographed 1 month apart (May-June 2021) Kuda Huraa
Coral Propagation – Monthly Progress
June was a busy month for us at Landaa, transplanting 56 new coral frames (using 4,000+ individual coral fragments) plus retransplanting 37 existing frames (3,000+ fragments), plus recycling a further 20 frames from the ‘Moon’ site (700+ fragments). A big THANK YOU to our resort colleagues for all their invaluable assistance in our efforts to regenerate the reefs this month. In addition, we also monitored 380 frames at various sites around the island, and updated the QGIS mapping.
At Kuda Hura, we transplanted two new coral frames and retransplanted eight existing frames. We also continued our Coral Watch monitoring, relocated (and cleaned) 310 frames at the Water Villas, and remapped (and cleaned) 89 frames at the Channel site. While monitoring the reefs, we spotted and removed seven crown of thorns starfish (COTs) plus a pillow starfish (Clucita sp.), which can be destructive to living corals.
- Water Villas site – our frames remain healthy, and no additional bleaching has been observed. The site continues to be an important nursery area for a great diversity of reef fish.
- Blue Hole site – most of the coral colonies remain stressed (either bleaching or fluorescing) and a few of the colonies have died.
- Channel site – our frames continue to fight against the smothering cyanobacteria and overgrowth of algae.
- Sea Star site – species of both Pocillopora and Acropora are thriving, and all colonies have regained their colour since the paling observed in March.
- House Reef site – on 14 June, our resort Dive Team colleagues helped with a new coral frame in the shape of a ‘Cinderella Carriage’, transplanted with 200+ fragments of Pocillopora. The growth and encrustation of the fragments will be closely monitored in the upcoming months.
Coral Plates in Aquarium One (plates KH01, KH02, KH05) and Aquarium Two (plates KH03, KH04, KH06)
Overall, the coral plates in both aquaria remain healthy. Plates in Aquarium-Two continue to collect more algae, and weekly cleaning is necessary to prevent coral mortality.
- KH01 (Acropora digitifera, A.millepora, Galaxea fascicularis) – fragments remain very healthy and encrusting.
- KH02 (G.fascicularis) – healthy, with significant growth (especially towards the top of the plate, with more light). Crabs broke one fragment, which we promptly reattached.
- KH03 (A.valida) – overall good health, however, the one bleached fragment is now almost dead.
- KH04 (A. digitifera, A. millepora) – healthy and encrusting correctly, despite continuing to present significantly more algal growth than the other plates.
- KH05 (G.fascicularis) – the fragments continue to adapt to last month’s 90-degree rotation.
- HK06 (G.fascicularis, new Feb-21) – continuing to grow steadily; the six lowest fragments have now fused.
Coral Bleaching Experiment
In order to identify the threshold at which a coral species can recover post-bleaching, we are trialling various parameters to promote recovery. Once the coral fragment has bleached, the heater is turned off and the water flow turned on, to allow the water to return to ambient ocean temperature. After a few days, the coral fragment displayed no signs of recovery, likely because the seawater is filtered (50um), and most zooplankton and rotifers are larger than this (food shortage could have hindered early recovery).
Therefore, after four days, we added 450ml of rotifers into the tank and turned off the flow for 24 hours to allow the coral to feed. Coral polyp movement was not visible after a few days, however, this is likely due to the fact the coral had died before feeding. Next, we hope to trial a variety of post-bleaching ‘feeding’ options in the coming months.
Coral Larval Workshop
This month, our coral biologist took part in a two-day workshop run by CSIRO and the Maldives Marine Research Institute. This was primarily to understand the best coral larvae collection protocols and to gain a more in-depth knowledge of rearing larvae for large scale restoration on Maldivian reefs.
One of the key benefits from this workshop was the collaboration with other scientists within the Maldives, to help identify spawning events (which are dependent on coral species and atoll).
The workshop consisted of:
- Coral Reproduction
- Larval Cultivation
- Technical processes of upscaling in previous countries
- Ability to conduct larval restoration in Maldives
Coral Cooling Experiment
The previous analysis from our cooling experiment (at one month) revealed that outside temperature significantly affected the closed-tank system water temperature. Fluctuations in water temperature were more variable in comparison to the open-flow system in which seawater temperature remained fairly constant. In the open-flow system, microfragment fusion of Galaxea was also seen, and fragments have self-attached to the plate, in comparison to the closed flow system in which Galaxea did not display self-attachment or fusion.
We have now started a new experiment in which both tanks are in closed-flow systems. One tank will be aerated overnight, to determine if this cools the water mass.
Coralwatch health chart – colour range of Acropora humilis corals
We started our Coral Watch surveys in May at the Water Villas site, and expanded to other sites around Kuda Huraa this month.
A total of 174 colonies from 68 frames have been monitored and photographed each week since mid-May and the 1200 photos from 11 surveys were individually analysed with Coral Watch methodology (recording the lightest and darkest colour for each coral colony in each survey).
- 7% coral colonies were identified as bleached/dead, mostly due to disease or overgrowth (cyanobacteria or filamentous algae) and not due to increased ocean temperatures.
- 59% coral colonies presented paling during one or more of the surveys; 41% were healthy throughout.
- Coral health by species: Acropora hyacinthus (55% healthy), digitifera (39%), A. humilis (23%) and A. tenuis (21%).
- Our best site for coral health and species diversity is the Water Villas.
Bleaching evolution of A.digitifera, growing on Reefscapers coral frames [photographed weekly, May-June 2021, Kuda Huraa]