Reefscapers Diary October 2021

Coral Propagation – Monthly Progress

At Landaa during October, we transplanted 1043 coral fragments onto 21 new coral frames (10 guest-sponsored, 10 hotel-sponsored, one online order). We also monitored (photographed, maintained) a total of 410 frames at various sites around Landaa Giraavaru, plus 30 old frames were recycled back onto the reef.

At Kuda Huraa this month, we transplanted 6 new coral frames and recycled a further 12 frames, using a total of 732 coral fragments (from 13 different coral species).

Water Villas (WV) – this site continues to be badly affected by the seasonally shifting sands in the lagoon, with one mid-October storm burying 17 frames overnight. We have been busy dismantling our aerial patterns, relocating 124 frames this month, bringing the yearly relocation total to 710 frames (including 30 recycled old frames).

The Dolphin-shape is at risk of the shifting sands, totalling 183 healthy frames that harbour a good diversity of mature coral colonies, with abundant resident populations of fish and invertebrates.
On 21 October, we spotted coral eggs on many mature colonies of Acropora tenuis. We hastily constructed several spawn-collection devices to harvest the eggs in-situ, but the spawning did not occur when predicted so we continued to monitor the corals closely. Changes in egg pigmentation were observed in Acropora tenuis, but the other Acropora hermaphroditic broadcasters were not yet close to spawning.

Blue Hole (BH) – we continue to remove the accumulated marine debris and drifting sea grass from this site, and the coral colonies remain healthy. On 27 October, mature coral eggs were spotted on colonies of Acropora secale (3m depth) and we observed coral spawning from 20:00 to 20:15 (Maldives time, GMT+5). We were able to harvest some eggs and placed them into our aquarium for observation, along with a dead coral skeleton as a settlement substrate. Some eggs were observed attached by 20:45 (30 mins after spawning) but we did not see coral larvae.
From our notes, we observed this spawning event occurred:
– 1.5 hours before the lowest tide (which was at 21:42);
– Seven days after the full moon (which was on 20 October);
– One day later than in Landaa Giraavaru (Baa Atoll).

Channel (CH) – 14 of the new monthly frames were located here, plus two mini coral frames, each with 19 fragments of Blue Coral (Heliopora coerulea, a reef-building octocoral with high resistance to thermo-stress and bleaching). A total of 54 frames were monitored and retransplanted (using fragments of Montipora digitata, Porites cylindrica and species of Acropora).

Sea Star (SS) – Aerial photographs of this site were taken to correct the QGIS location mapping, and we plan to construct a new aerial crab-shape.

House Reef (HR) – the temperature logger was redeployed on 8 October, and we removed two corallivorous predators (one Cushion starfish, one Crown of Thorns). The two new monthly coral frames at this site were transplanted with species of Acropora and Pocillopora verrucosa.

Coral Plates in Aquarium One (plates KH01, KH02, KH05) and Aquarium Two (plates KH03, KH04, KH06)

• KH01 (Galaxea fascicularis; Acropora species replenished Sep-Oct 2021) – added six new fragments of Heliopora coerulea.
• KH02 (G. fascicularis) – algal overgrowth has caused some coral tissue death.
• KH03 (Acropora species, replenished July 2021) – healthy and encrusting.
• KH04 (A.digitifera, A.millepora) – healthy and growing well.
• KH05 (G.fascicularis) – fragments continue to grow and fuse; cyanobacterial growth regularly removed.
• KH06 (G.fascicularis) – steady health, growing, fusing.

Preparation for Coral Spawning

This month, we took part in the second series of a two-day online coral larvae workshop in partnership with CSIRO, the MMRI and MUI (among others) to further understand and identify coral spawning events across the Maldives. This informative workshop detailed the use of coral larvae in reef restoration, to upscale future efforts. It is evident that sexual propagation will result in higher genetic diversity amongst species in comparison to asexual propagation. Moreover, corals are extremely fecund, meaning a large number of juvenile corals could be produced if mortality at early life stages of fertilisation and settlement are reduced. This technique could enhance coral propagation programs here in the Maldives, if the asexual technique is coupled with sexual broadcast spawning and rearing.

At Marine Savers, we have transplanted and grown many different species of corals over the years which are large enough to produce mature spawning colonies. Our large database allows us to pinpoint transplantation dates, identify age of maturity, track mature colonies, and record coral spawning across multiple years. This data can be used to ensure genetic diversity, as we can confirm gamete collections from different frames based on these dates.

To expand our knowledge of coral spawning around Landaa Giraavaru, we reviewed the data from our previously documented spawning events (2013 – 2020). It is incredibly difficult to predict when coral might spawn, therefore it is important to take note of tidal cycles, lunar cycles, and water temperatures from previous years, to be utilised as indicators for predicting spawning this year.