Reefscapers healthy Acropora corals Maldives

healthy Acropora coral colonies growing on our frames

Monthly Progress

At Landaa, we transplanted 21 new coral frames (thanks largely to a very generous online donation) and we monitored and photographed a further 115 frames (mainly at the Dive and Stingray sites).

At Kuda Huraa, we monitored (cleaned and photographed) 40 coral frames, and cleaned a further 353 frames, ready for transplantation later in the year. We noted that some Acropora digitifera colonies appear to be recovering from bleaching (photos below), whereas the newly transplanted fragments (from July) are healthy and have started to encrust onto the frames.

At the Channel site, we noted the colonies that survived the bleaching have regained colour and are now growing well. We continued to repair any broken tags and started GPS mapping of the south part of the channel. We also thinned-out and relocated some Montipora coral colonies that were dominating their Acropora neighbours.

At the Blue Hole site, we continued to place further frames upon rubble, as it seems to be helping prevent them from sinking into the sand. At the Spa site, increased sedimentation and accumulation of sand has caused most of the fragments to die, although a few fragments of Acropora and Pocillopora are surviving.

Reefscapers Acropora coral bleaching Maldives
Reefscapers Acropora coral bleaching Maldives

Coral Plates in Aquarium One (plates KH01, KH02, KH05) and Aquarium Two (plates KH03, KH04)

  • KH01 – the newly replenished fragments of Acropora digitifera and Acropora millepora have regained a healthy colouration and have now started to encrust onto the plate.
  • KH02 – the Galaxea fascicularis fragments remain healthy overall, and the fragments are fusing with one another (although seemingly at a slower rate).
  • KH03 – thoroughly cleaned of algae. The calcified areas are growing and about to fuse. The fragments of Acropora valida remain healthy and continue to grow, although they haven’t yet calcified onto the plate.
  • KH04 – also cleaned of algae. Only two original fragments remain (due to the loss from algal overgrowth) and of the 11 newly transplanted fragments, 4 have started to calcify onto the plate.
  • KH05 – 1 fragment died after bleaching, but the others have now regained a healthy colouration and continue to grow (2 fragments are encrusting).
Reefscapers Acropora valida coral KH03

Acropora valida growing on plate #KH03

Coral Reproduction Spawning Experiment

In our coral reproduction study, algal growth had started to cover the coral fragments, so we cleaned the rocks to reduce the effects of competition. Some smaller colonies declined in health, with reduced polyp activity and noticeable colour change, whereas the larger colonies were better able to cope with the algal competition and actually grew in size.

Reefscapers coral reproduction experiment algae
Reefscapers coral reproduction experiment algae

‘Coral Core’ Experiment

Health has remained stable in all the remaining coral plugs, except for R3 (Medium-2), which has deteriorated on the Coral Watch Health Chart from a ‘5’ to a ‘1’ (completely bleached). It is unclear what has triggered this response in previously healthy tissue, but perhaps it is in response to localised predation (as no evidence of sedimentation or other stressors could be identified, and the neighbouring plug is healthy).

Plug R2 (Large-1) has maintained good growth and has continued to spread over the substrate. The Medium plugs, from the same replicate, continue to maintain good health.

R1PlugsAll 6 were lost (no epoxy) or have died (4 weeks after transplantation; due to sedimentation?)
ParentQuickly recovered from slight bleaching, new tissue growth in the cavities.
R2Plugs3 plugs died; 3 plugs in excellent health (regained colouration, encrusting well).
ParentVery healthy, with good recovery around and over the holes; new tissue growth in the cavities.
R3Plugs3 plugs now dead; 2 plugs healthy; 1 plug newly bleached (August 2020).
ParentVery good health, with encrusting over the Epoxy for all 6 holes (but no new tissue growth.
R4Plugs[Vertical outplanting] 2 plugs dead; 4 plugs pale.
ParentVery healthy encrusting for all 6 holes (impossible to distinguish the removal sites).
Reefscapers coral core experiment R2-L1

Coral core experiment R2-L1

Reefscapers coral core experiment R3-M1&2

Coral core experiment R3-M1&2

Time Lapse Experiment to Record Coral Bleaching

This month, we successfully captured the time-lapse bleaching process for a second time, and recorded the release of a gas during the bleaching process (seen as bubbles on the fragment surface). We are unsure what the gas is, or the process behind its formation, but there are several scientific theories:

  1. Carbon Dioxide (C02) – Corals use dissolved inorganic carbon from seawater to create their calcium carbonate skeleton, producing carbon dioxide as a by-product. This CO2 can enhance the ability of zooxanthellae to complete photosynthesis. The calcification process can accelerate during the initial stages of bleaching, so these visible gas bubbles could be excess CO2 being expelled.
  2. Reactive Oxygen Species (ROS) – A type of unstable oxygen-containing molecule that reacts easily with other molecules in a cell. A build-up of ROS in cells may cause damage to RNA, DNA and certain proteins, and may cause cell death. High rates of photosynthesis can generate large quantities of dissolved oxygen that can form ROS. The zooxanthellae and polyp contain adaptations to manage ROS (to prevent cell damage) that can become overwhelmed during stress, perhaps expelling ROS bubbles in the process.
  3. Oxygen (O2) – During the initial phase of bleaching, there is a rise in photosynthetic rates and oxygen-production. Due to the low water flow rate in our aquarium, the oxygen may become trapped on the branchlets as visible bubbles (whereas under normal circumstances, there would be a breakdown of the boundary layer and the release of oxygen would not be visible).