Coral Propagation – Monthly Progress
At Landaa during July, we transplanted 36 new coral frames (24 guest-sponsored, 11 Resort-sponsored, one online order) adding a total of 2400 coral fragments onto the reef. We also monitored (cleaned, repaired, photographed) 108 coral frames at various sites around the island.
We are continuing to build our generous guest sponsorship of 50 large frames, adding a further 13 frames this month to give a total of 35 frames at Mudikaashi Reef (an area of degraded reef at the Dive Site). To ensure genetic diversity at this large new site, we have spent time harvesting coral fragments from all around Landaa Giraavaru. So far, we have repopulated this area with 3710 coral fragments, with a further 1590 fragments to go (15 remaining large frames.)
At Kuda Huraa this month, we transplanted 11 new coral frames (nine guest-sponsored, two Resort-sponsored). Additional coral work included monitoring and mapping at the House Reef, and extensive maintenance work in the Channel site by our apprentices.
Coral Bleaching Monitoring
Coral colonies across different temperatures and bleaching outcomes from earlier this year were photographed in our shallow coral propagation sites: the Water Villas, and the Turtle (rescue coral).
- The Water Villas is a shallow site with well-settled coral and optimum health. Corals of different species, colours and sizes were monitored for a period of 91 days. 16% of 400 corals presented signs of severe paleness or bleaching, but we saw recovery rates of 100%. (The Drupella outbreak that occurred after the bleaching season destroyed several colonies due to their higher susceptibility.)
- The shallow Turtle site is populated by newly imported rescue corals (with relocation stress) and so higher bleaching rates were observed (32% of 200 corals). We monitored this site for 73 days; although many corals did not recover, the colonies that did survive have now recovered well.
- Resilience of coral morphs: Green > Purple > Brown.
Published studies (Satoh 2021) find that brown morphs are more susceptible to bleaching (and death) than purple morphs, whereas green morphs appear to be the most resistant to thermal stress (as they maintain photosynthetic activity).
- NOAA Satellite and Information Service. (2019)
- Noriyuki Satoh et al (2021) – Colour morphs of the coral Acropora tenuis, show different responses to environmental stress and different expression profiles of fluorescent-protein genes, G3 Genes, Genomes, Genetics, 11(2).
Our control small-sized coral frames were monitored to estimate survival rates across the sites: 64% survival on average, but only 48% at the Channel site. Corals in the shallow areas of the House Reef and the Turtle site exhibited better health, possibly due to fewer corallivores (such as Crown of Thorns (COTs) and Drupella snails.)
At Kuda Huraa during 2021-2022, gametes have been observed in 12 different species, with actual spawning events witnessed and recorded in four species.
During July, we conducted five surveys (at night) to look for signs of coral spawning.
- Starfish site – white eggs in two species (A. humilis, A. secale).
- Water Villas – pigmented eggs in three species (A. digitifera, A. latistella, A. muricata); due to the later absence of gametes, we assumed that spawning occurred on 14 July in both A. digitifera and A. latistella.