Monitoring for signs of coral bleaching – Acropora colonies on our frames, photographed 1 month apart (May-July 2021) at Kuda Huraa
Coral Propagation – Monthly Progress
At Landaa, we transplanted 30 new coral frames, sponsored by guests (15), the Resort (13) and online (2), using a total of 1537 individual coral propagation fragments. We also monitored (cleaned and photographed) a total of 135 frames at various sites around the island, and sent out the regular updates to our kind sponsors.
We also focused on recycling and relocating older coral frames, with the help of a simple ‘raft’ made from three unused paddleboards. Frames were cleaned of dead corals and algae, and replanted with healthy new coral fragments (mainly species of Acropora and Pocillopora). This way, we added a total of 790 new coral fragments to the reefs around Landaa (including Bissie’s Reef, and select frames at the Coral Trail and Dive Site). In addition, we removed and cleaned a further 50 frames and sent them to Voavah for recycling.
A total of 1533 new fragments were transplanted, from a variety of coral species (Pocillopora verrucosa, P. meandrina, Acropora tenuis, A. vermiculata, A. digitifera, A. gemmifera, a. humilis, A. loripes, A. muricata, A. hyacinthus, A. grandis).
- Water Villas – corals remain healthy; any broken colonies from our relocation exercise were quickly retransplanted onto other frames.
- Turtle site – two additional frames were lost due to shifting lagoon sands (bringing the total to six).
- Blue Hole – mostly healthy, with some mortality. We harvested healthy donor fragments for the travel-group frames from here (subsequently deployed at the House Reef site).
- Channel – continued remapping the northern area (230 frames now mapped); cleaned affected frames of algae; repositioned 40 sunken frames.
- Sea Star – corals are very healthy; some Pocillopora colonies were found broken or unattached from their frames (due to unknown reasons) so these were reattached.
- House Reef – one Pillow starfish and two Crown of Thorns starfish (COTs) were removed; 24 frames have been recently deployed in this site; dedication tags were added to 15 frames.
- A heart-shaped frame [KH2833] was transplanted with Pocillopora fragments to commemorate PADI Women’s Dive Day (12 July).
Coral Plates in Aquarium One (plates KH01, KH02, KH05) and Aquarium Two (plates KH03, KH04, KH06)
- KH01 (Galaxea fascicularis; Acropora species replenished July 2021) – original fragments remain healthy and fusing. Twenty new Acropora fragments were attached to the plate (A. tenuis, A. digitifera, A. gemmifera, A. hyacynthus).
- KH02 (G.fascicularis) – overall healthy; upper fragments (closer to the light source) continue to grow faster.
- KH03 (Acropora species, replenished July 2021) – original fragments are in good health; 15 new Acropora fragments were added to the plate (A. tenuis, A. vermiculata, A. digitifera).
- KH04 (A. digitifera, A. millepora) – healthy and growing well.
- KH05 (G.fascicularis) – well-adapted, continuing to grow and fuse.
- HK06 (G.fascicularis, new Feb-21) – healthy, growing, fusing.
Coral Bleaching Experiment
A fragment of Galaxea fascicularis was placed into our aquarium and allowed to acclimatise for 24 hours before starting our coral bleaching observations. Coral bleaching occurs due to elevated temperature (and light intensity), leading to photo-oxidative stress within the coral.
After a few days of increased water temperature, the coral tissue demonstrated a high degree of swelling, likely due to the coral expelling symbionts (no additional nutrients were added to the water, which have been shown to effect polyp extension and coenenchyma swelling).
- Morris et al. (2019) – explained that nutritional mechanisms may be a factor, in which a “coral–Symbiodiniaceae symbiosis shifts from a mutualistic to a parasitic relationship under thermal stress”.
- Landsberg et al. (2020) – identified the disruption of zooxanthellae physiology in ‘Stony Coral Tissue Loss Disease’ and described similar ‘swelling’ (and necrosis).
- Kerswell & Jones (2003) – concluded that low-salinity seawater “involves impairment of the capacity of the algal symbiont for photosynthesis” that could prompt the dissociation of the coral-algal relationship during unfavourable conditions.
- Morabito et al. (2013) – revealed that when jellyfish (Cnidarian family, same as corals) are exposed to hypoosmotic media, the cells ‘swell’ within minutes.
On 12 July, we conducted a rapid health assessment of the east side of Landaa by using quadrats along the reef crest (see map ‘Points’). Within a given area, we can estimate percentage cover of specific categories of benthic communities (hard coral, soft coral, sponge, algae, etc).
We used 14 quadrats (2 m x 2 m) along a 1.5 km radius. Unknown species were photographed for later identification as part of our time-effective estimation (a future LIT survey would be more accurate).
- Most common hard coral species: Porites, Pocillopora, Brain corals, Galaxea fascicularis.
- Locations one to ten showed a higher degree of coral diversity.
- Location 5 revealed the highest degree of benthic diversity (14 species).
This month, we retrieved our temperature loggers from the lagoon at Kuda Huraa, and plotted temperature profiles for the recorded sea surface temperatures (SST) from 30 April to 2 July 2021.
- The temperatures decreased significantly after 26 May.
- Highest recorded temperature was at the Sea Star site.
- The SST averages from the three sites are very similar.
- Compared to March-April, SSTs for May-June decreased by 0.4°C (consistent with regional SST values reported by NOAA Coral Reef Watch).