juvenile coral polyps (Acropora humilis) uptake of symbiodinium Reefscapers Maldives

Uptake of symbiodinium in our juvenile coral polyps (Acropora humilis)

Coral Spawning in the Maldives 2022 Q3-Q4 Updates

Please also see our main Coral Spawning reports page, from 2013 onwards, including our pioneering lab work in Oct-Nov 2021.

July 2022 Observations

Tracking Gametogenesis

This month we located immature oocytes in: Acropora tenuis, A. plantaginea, A. humilis, A. secale, A. rosaria, A. latistella.
Thus far we have located immature oocytes in nine species of Acroporidae from 72 various colonies. This is ongoing and we hope to locate more colonies from a larger sample area around Landaa.

Coral Settlement Update

Our settled Acropora polyps from Oct-Nov 2022 are healthy and continue to grow well. Regular maintenance includes removing competition (algae) and keeping tanks clean. Due to the aggregation of larvae upon settlement, juveniles are beginning to ‘fuse’ together and continue to thrive.

Published research describes aggregated larval settlement as chimerism (defined as ‘a single organism composed of cells with more than one distinct genotype’). This could be a competitive strategy to minimise early life mortality and enhance growth rates.
Puill-Stephan (2012) described Acropora millepora chimeras as threefold larger compared to solitary juveniles, while Giordano (2021) identified Mediterranean red coral chimeras to be 40% larger.

To assess growth of juveniles once outplanted onto the reef, we have attached a few fragments onto a mini frame and placed it on the House Reef. After only a few days, the recruits were damaged by predation (likely by parrotfish). Venera-Ponton (2011) demonstrated that removal of algae led to enhanced coral growth rates but increased predation of the juvenile corals by parrotfishes.

  • Giordano, B., & Bramanti, L. (2021). First report of chimerism in Mediterranean red coral (Corallium rubrum). Mediterranean Marine Science (Vol. 22, Issue 1).
  • Puill-Stephan, E., et al (2012). High potential for formation and persistence of chimeras following aggregated larval settlement in the broadcast spawning coral, Acropora millepora. Royal Society B: Biological Sciences, 279(1729).
  • Venera-Ponton, D. E., et al (2011). Macroalgae reduce growth of juvenile corals but protect them from parrotfish damage. Marine Ecology Progress Series, 421.
Reefscapers settled Acropora millepora

Coral polyp growth (Acropora millepora)

Reefscapers settled Acropora fusion

Fusion of settled Aropora polyps

August 2022 Observations

Environmental Data

In anticipation of the upcoming coral spawning events in the Maldives, we have created a new spreadsheet to track environmental data, including precipitation, weather, wind speed, lunar phase, and moon illumination. We have placed two HOBO loggers onto the reef, to record water temperatures at depths of 1m and 5m, located at the same site as recent spawning events (Oct-Nov 2021 and Mar-Apr 2022) to ensure continuity. We will also compile data from the following sources:

Coral Spawning Protocols

To maximise our efforts for coral gamete collection, we have built four more collection devices from 500-micron mesh. These structures are larger than previous devices, to ensure we collect the maximum number of gametes, from multiple colonies of the same species. The extra four nets will allow us to collect from two different species in a single night, maximising our fertilisation and settlement process.

In addition, we have created new protocols outlining our experimental work.

  • We will estimate egg densities to calculate the number of eggs that successfully reach the planulae and settlement stages. We can then quantify success rates to calculate the overall robustness of our methodology.
  • To better understand resilience, we will rear juvenile larvae exposed to different temperatures over a few months, to assess if pre-exposure to heat can prime recruits to better withstand future thermal stress.
  • To upscale our restoration practices, we will force settlement onto areas of degraded reef, to assess survivorship in-situ.

Coral Spawning Surveys

At Kuda Huraa during August, we conducted five surveys covering different species across all our coral propagation sites, and found gametes (mostly immature) on 27 wild and local colonies of Acropora species. We also found mature brown oocytes in one colony of Sarcophyton; this species can be either gonochoric or hermaphrodite, and oogenesis takes up to 24 months. Globally, spawning occurs in Nov-Feb (Australia), March (South Africa) and July (Red Sea), as described in Benayahu 1986, Schleyer 2004, Hellstrom 2010.

At Kuda Huraa during a 12-month period from 2021-2022, we have observed gametes in 14 species, and witnessed actual spawning events in four species; from our records, we can see that gamete development takes an average of 67 days.
From our surveys this month, we observed gametes in 48% of colonies, and only in the following corals: Acropora digitifera, A. gemmifera, A. humilis, A. secale, A. plantaginea, Sarcophyton sp., Acropora sp.1 (possibly A. rosaria), Acropora sp.2 (possibly A. retusa).


  • Benayahu & Loya (1986). Sexual Reproduction of a Soft Coral: Synchronous and Brief Annual Spawning of Sarcophyton glaucum (Quoy & Gaimard, 1833). Biological Bulletin, 170(1), 32–42. doi:10.2307/1541378
  • Hellström, Kavanagh & Benzie (2010). Multiple spawning events and sexual reproduction in the octocoral Sarcophyton elegans (Cnidaria: Alcyonacea) on Lizard Island, Great Barrier Reef. 157(2), 383–392. doi:10.1007/s00227-009-1325-8
  • Schleyer, Kruger & Benayahu (2004). Reproduction and the unusual condition of hermaphroditism in Sarcophyton glaucum (Octocorallia, Alcyoniidae) in KwaZulu-Natal, South Africa. Hydrobiologia 530, 399–409 (2004). doi: 10.1007/s10750-004-2683-3
  • Swanson, Bailey, Schumacher, Ferguson, Vargas-Ángel (2018). Ecosystem Sciences Division standard operating procedures: data collection for rapid ecological assessment benthic surveys. NOAA technical memorandum NMFS-PIFSC ; 71. doi : 10.25923/39jh-8993
  • Aeby, Shore, Jensen, Ziegler, Work, Voolstra (2021). A comparative baseline of coral disease in three regions along the Saudi Arabian coast of the central Red Sea. PLoS ONE 16(7): e0246854. doi: 10.1371/ journal.pone.0246854 TURTLE BIOLOGY

August 2022 Spawning Event
Kuda Huraa, North Malé Atoll, Maldives

  • 12 August: a Full moon/Supermoon.
  • 12-13 August
    Acropora digitifera at the Water villas, 0.5m depth.
  • 12-13 August
    We sighted the characteristic surface slick of pink/orange gametes from an unknown broadcaster species at the Back Jetty site. We collected a large sample of the spawn and transported it to our Fish Lab, where we followed our protocols:
  • Spawn was gently stirred for 1 min in intervals of 5 min (for a total of 20 min) to induce bundle dissociation.
  • The eggs were scooped out and transferred to a tank with a low drainage pipe (to remove leftover sperm).
  • After 30 mins, samples were analysed to look for signs of fertilisation (none observed).
  • By the six-hour mark, it was obvious that the eggs had degraded due to low rate of flow in the aquarium.
Reefscapers coral spawn process

September 2022 Observations

Coral Spawning at Landaa

Coral spawning can occur in the Maldives during the month of September, but we have not yet recorded the presence of pigmented gametes in any Acropora colonies. So as not to miss any events, we conducted in-water night surveys around the September full moon for seven nights, and around the new moon for three nights. Unfortunately, we did not observe any bundling, spawning or coral slicks.

We are continually checking our coral frame colonies and wild colonies for changes in gamete colour (indicating maturation and upcoming spawning). So far at Landaa we have recorded:

  • White eggs in eight species of Acropora (A. plantaginea, A. secale, A. tenuis, A. humilis, A. rosaria, A.valida, A.aspera, A. squarrosa).
  • Pale pigmented eggs in two species (in secale and A. humilis).
Coral Spawning at Kuda Huraa

This month we conducted 12 surveys to look for coral gametes of different species at our coral propagation sites and the reef flat that surrounds the island. We found that 41% of the 125 coral colonies checked since August presented gametes, adding 25 colonies of Acropora species to our monitoring this month.

Most corals have non-pigmented eggs, although one colony of Acropora digitifera from the Water Villas was recorded with mature eggs (first observed with mature eggs on 23 May 2022, 100 days ago!)

  • 8 September – coral slick from unknown broadcaster at the Back Jetty (sunrise side)

Gamete Monitoring

Wild, relocated, and local coral colonies continue to be regularly monitored in five different sites around Kuda Huraa.

  • 7 September – eggs found in gemmifera, A. humilis, A. plantaginea.
  • 17 September – eggs found in tenuis, cf A. tenuis.
  • 18 September – eggs found in secale, A. muricata, A. millepora.
Reefscapers coral spawning Acropora immature eggs

White immature eggs in Acropora

Reefscapers coral spawning Acropora pale eggs

Pale-pigmented maturing eggs in Acropora