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 A. gemmifera, A. humilis, A. plantaginea.
  • 17 September – eggs found in A. tenuis, cf A. tenuis.
  • 18 September – eggs found in A. 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

October 2022 Spawning Events

Coral Spawning at Kuda Huraa

This month at Kuda Huraa, we recorded spawning at the Blue Hole site (depth 3m) in Acropora secale and A. plantaginea. We collected gametes – fertilised ex-situ, and settled successfully. The development and health of the coral larvae is closely monitored and documented through routine microscopic examinations. Larval feeding began on day-5, using a krill-based food source (‘Coralific Delite’).

Gamete Monitoring – This month, in addition to our daytime gamete checks at six sites around Kuda Huraa, we conducted 16 separate night surveys to look for spawning at the House Reef and Blue Hole sites. We found 48% of 142 colonies checked since July presented gametes, adding up to a total of 67 monitored Acropora colonies. Pigmented gametes [PHOTOS] were recorded in: A. secale, A. plantaginea, A. tenuis, A. muricata.

Reefscapers coral spawn Acropora secale collection fertilisation process

coral spawn collection fertilisation process (Acropora secale)

Reefscapers coral gametes mature
Reefscapers coral gametes mature

Coral Settlement Update in our Lab

From the March 2022 spawning event, our settled juvenile corals of Acropora millepora continue to grow and thrive in our lab aquaria after six months.

Reefscapers Acropora millepora juveniles 6-months

Acropora millepora juveniles (6-months)

Reefscapers Acropora millepora juveniles 6-months

Acropora millepora juveniles (6-months)

Wild Colony Gamete Check and Tagging

To study any discrepancies in coral spawning synchronicity of frame and wild colonies, we have increased our survey area to include a ‘bommie’ (a natural coral outcrop). Here, we have tracked gametes from pale to pigmented, as they matured in multiple wild colonies, and tagged them for later identification during night dives.

Coral Gametogenesis

To better understand the difference in gametogenic cycles of a variety of Acropora species, we have been documenting changes in gamete pigmentation over time. We have observed the progression of maturing gametes as follows: white (in July), pale pigmentation (September), pigmented (late October).
This month, we recorded pale and pigmented gametes in both wild and frame colonies of eight Acropora species: A. secale, A. humilis, A. plantaginea, A. rosaria, A. globiceps, A. tenuis, A. valida, A. squarrossa.

Coral Spawning at Landaa Giraavaru

October represents the second year running in which we have collected data on coral spawning consistently around Landaa Giraavaru (see 2021 report).

  • 5 October – we observed pigmented gametes in one wild colony (Acropora globiceps) and seven frame colonies (A. secale, A. humilis, A. plantaginea). Interestingly, these are the only colonies that had pigmented by the start of the month.
  • 10 to 17 October (19:00 – 22:00 MV time) – we conducted nightly surveys.
  • 10 October (Full Moon) – published research has identified an inter-annual variation of spawning synchronicity in relation to lunar phases (Sakai 2020), sometimes giving rise to ‘split-spawning’ over two consecutive months (Gilmour 2016). This is apparent in our spawning observations this year (not all coral species presented maturing gametes).

Published research has shown that the duration of a period of calm winds is directly related to the length of the spawning period, which would maximise fertilisation rates (van Woeski., 2010). Interestingly, the weather this month brought strong winds, large waves, and sedimentation (not the calm weather we have previously observed during spawning). We observed that spawning was correlated to a decrease in wind speed and a decrease in lunar illumination. Research has shown that moonlight acts as a regulatory factor to determine coral spawning events, with the period of darkness between sunset and moonrise triggering mass spawning (references below).

  • 23 – 31 October (19:00 – 22:00 MV time) – we conducted nightly surveys around sunset and low tide. A total of 10 colonies spawned this month, taking our database totals to 58 recorded spawned colonies. All spawned colonies were measured, and ecological volumes calculated.
Coral A. humilis bundling Reefscapers

A. humilis bundling

Coral A. humilis spawning Reefscapers

A. humilis spawning

November 2022 Spawning Events

Coral spawning in Acropora Maldives Reefscapers

Coral Spawning Preparation

Following on from October’s coral spawning event, we continued to track species-specific coral spawning patterns into November. As this is the second year running that we have collected data at this time of year, we are particularly interested in understanding spawning cycles on a temporal scale. To assess both wild and frame coral spawning, we split into two teams to cover a larger area and to track wild spawning on a ‘coral bommie’ just off Landaa. We collaborated with our Four Seasons colleagues and the Dive Team (thanks, everyone!) to ensure safe night-working practices.

Environmental Cues

  • Environmental factors prior to spawning months include precipitation (Mendley 2002), rise in sea surface temperature (Keith 2016), and regional wind fields (van Woesik 2009).
  • Environmental cues that are linked to the synchronised release of gametes include lunar cues (Kaniewska 2015), sunset times, and solar light cycle (Sweeney 2011; Brady 2009; Babcock 1986).

Utilising both the scientific literature and our own knowledge from 2021 spawning patterns allowed us to better understand the spawning events this year. Although our temporal data is still limited, we are beginning to formulate ideas on spawning synchronicity of a variety of Acroporidae within the Maldives, to better predict these events in the future.

Upon identification of environmental cues around the full moon (8 November) and new moon (24 November), we started nightly in-water surveys between 17:00 and 22:00. Interestingly, November’s full moon was a total lunar eclipse. This takes place when the ‘Earth comes between the sun and moon and its shadow covers the moon’.

Coral spawning Maldives Reefscapers
Coral spawning mature eggs Reefscapers

Average Environmental Conditions

From our own observations, it seems that coral spawning might be linked to:

  • a decrease in lunar illumination,
  • stable average sea surface temperature,
  • zero precipitation.

During November, peak spawning dates occurred when wind speed increased (although average monthly wind speed for November was much lower than during October).

Decrease in wind speeds during spawning months in comparison to preceding months have been shown as advantageous to increased fertilisation success (Rosser 2008; van Woeski 2009).

Identifying Mature Colonies

Nightly gametogenic surveys were conducted to identify the presence of pigmented gametes. During November, we observed a change in gamete pigmentation from pale to highly pigmented in several Acroporidae including:

A. secale, A. plantaginea, A. rosaria, A. tenuis, A. squarrosa, A. humilis, A. globiceps, A. aspera.

Colonies with eggs were then tagged with red/white tape to identify them during nights of coral spawning.

Coral Spawning – November

During November, a total number of 196 colonies were closely observed while spawning, with key timings collected over the full moon and new moon periods. Although we saw many more corals were spawning, we limited ourselves to collecting more complete data from a select number of colonies (mainly on our coral frames, with a few wild reef colonies).

We are collating data for a more complete write-up, but nightly highlights included:

  • 43 Acroporid colonies were observed spawning, mainly plantaginea and A. tenuis, with some A. secale, A. humilis, A. retusa.
  • 65 Acroporid colonies were observed spawning, mainly A. plantaginea, A. secale and A. humilis, with several A. tenuis, A. aspera, A. squarrosa.
  • 26 Acroporid colonies were observed spawning, mainly A. plantaginea, A. tenuis and A. humilis, with a few A. secale, A. squarrosa, A. rosaria.
  • 30 Acroporid colonies were observed spawning, mainly A. plantaginea, with several A. rosaria, A. retusa, A. tenuis.
Coral spawning mature eggs Reefscapers

Collecting Coral In-situ

As Acroporid coral gametes are buoyant, they float to the surface and can be collected using a variety of methods. Our 2021 collection devices were utilised again this month, along with four new larger nets. Nets were placed on tagged frames during the predicted spawning dates. Attachment took ten minutes per net utilising SCUBA or freediving techniques, with a total of eight nets placed in-water at various locations at our Dive Site. The plastic collection bottles were labelled to keep track of gametes before fertilisation, to differentiate between the species collected.

This year, our key aim was to collect gametes from both wild and frame colonies to ensure genetic diversity, while recording discrepancies in coral spawning synchronicity (for both wild and frame colonies).

November Spawning at Kuda Huraa

Coral Spawning

This month, our Kuda Huraa team divided across two sites for 18 nights of spawning surveys around the time of the full moon. To further maximise our data collection, we also conducted morning surveys, to check for presence of gametes at unmonitored sites.

We successfully observed and documented a total of 52 coral colonies, spawning over eight nights in five locations, representing six different species: Acropora tenuis, A. plantaginea, A. humilis, A. retusa, A. secale, A. rosaria.

We collected gametes from five coral colonies of A. tenuis (from frames at the Blue hole and Water Villas sites), fertilised them, and observed successful settlement on substrate.

Gamete Monitoring

A total of nine species of wild, relocated, and local colonies (at six different sites around Kuda Huraa) were found to have gametes: Acropora monticulosa, A. gemmifera, A. humilis, A. plantaginea, A. millepora, A. tenuis, A. cf. tenuis, A. muricata, A. retusa.

Coral larvae development Reefscapers Maldives
Coral fertilisation settlement Reefscapers Maldives

Larval Development

  • Acropora tenuis – larvae have continued to grow since settlement, but have not shown signs of symbiont (zooxanthellae) uptake.
  • Acropora secale – due to water flow problems in our coral pool, most larvae became stressed and consequently lost their pigmentation. Microscopic analyses revealed that some of the larvae were starting to uptake symbionts. As the month progressed, the symbiont density within the larvae greatly increased (darker colouration).
  • Algal removal – we trialled the addition of snails (Trochus species) to control algal growth, but this seemed to adversely affect the coral larvae. We have now resorted back to gently brushing the rubble substrate with toothbrushes, while continuing to research alternative methods.


Fertilisation and Embryogenesis

Gamete bundles of A. tenuis were collected in-water from four frames (six colonies) and mixed ex-situ into four separate buckets of fresh seawater. Gentle mixing for 30 minutes dissociated the gamete bundles and allowed fertilisation to take place.

Post-mixing, eggs were further separated from sperm mixture and placed into four open-flow tanks with specialised drainage.

We worked overnight to accurately track the embryogenesis developmental stages, and successfully observed blastomere development from early evening to mid-morning the following day.

Approximate milestones for A. tenuis include:

  • Day #1 at 20:30 – first 2-cell blastomere cellular divisions
  • 21:00 – 4-cell blastomere divisions
  • 22:00 – both 4- and 8-cell blastomeres
  • 22:30 – 16-cell blastomeres
  • 23:00 – morula stage
  • Day #2 at 02:30 – prawn chip shape
  • 04:30 – bowl
  • 08:00 – round
  • 10:00 – tear drop
  • Day #3 at 09:00 – fully formed planulae

The same procedure was followed for gamete bundles of A. secale (collected in-water from eight colonies of both wild and frame colonies). A similar timeline was observed, however, overall development was slower and took an extra 24 hours from fertilisation to planulae (development slowed from the ‘bowl’ stage, onwards).

Settlement Success

  • Both A. secale and A. tenuis have settled and metamorphosed into juvenile coral polyps, but they have not yet fully taken up their symbiodinium (symbiotic zooxanthellae).
  • One year from initial settlement, A.plantaginea is continuing to grow nicely in our open-flow tanks systems.
Coral spawning settlement of A.secale

Settlement of Acropora secale

Coral spawning settlement of A.planaginea at 1 year

Settlement of Acropora plantaginea at 1 year


We have been plotting our coral spawning data to visualise differences in species-specific spawning times from our observational data (2021 and 2022 at Landaa Giraavaru). The majority of Acropora species spawned at similar times, and spawning on our frames compared with wild colonies was very similar for each species observed. We will run statistical analysis to confirm any correlations, and use visuals for baselines.

Studying the abundant literature on coral spawning for various Acroporidae from around the world, it is apparent that certain species (notably A. tenuis) spawn around sunset, compared to other species that spawn hours later (Harrison 1984; Hayashibara 1993; Fukami 2003; Baird 2022). Our own observations at Landaa and other Reefscapers sites are in accordance with this.


December 2022 Spawning Events

Reefscapers coral spawning monitoring Acropora tenuis

Coral spawning monitoring – Acropora tenuis colonies (Kuda Huraa, December 2022)

Coral Spawning at Landaa

  • 8 December (full moon) – we started nightly snorkels around the full moon period.
  • We observed spawning in five frame colonies of tenuis.
  • Several days later, we observed spawning in 18 frame colonies of plantaginea.

🗓️ Reefscapers 2022 Key Findings – Coral Spawning

  • A total of 15 Acroporidae and one Goniastrea from 341 colonies were recorded spawning.
  • We tracked key bundling and spawning timings, oocyte development and embryogenesis.
  • Utilising our methodologies developed in 2021, we successfully collected, fertilised and settled four Acropora species (A. tenuis, A. secale, A.millepora, A. digitifiera).

Gamete Monitoring at Kuda Huraa

Currently, nine species of corals continue to be monitored, across five different sites around Kuda Huraa. We have been monitoring gametes in some colonies for five months during 2022!

Coral Spawning

In Kuda Huraa, we set our own new record this month for the greatest amount of coral spawning recorded!

  • 20 spawning monitoring surveys were conducted; gametes were present in ten species at all four sites.
  • We witnessed 153 colonies (of eight species) spawning over three nights, across four locations. This was mainly in colonies of Acropora tenuis (66%) but also: plantaginea, A. digitifera, A. humilis, A. gemmifera, A. retusa, A. monticulosa, A. muricata.

Coral Settlement

  • This month, gametes were collected from Acropora muricata, fertilised, and successfully settled in our Lab.
  • Over the past three months, our settled coral species continue to present steady health (three species: secale, A. tenuis, A. muricata). Symbiont (zooxanthellae) uptake was first observed in A. tenuis on 18 December, and is now present in most of our tiny coral polyps. Our A. secale polyps continue to darken as they take up further symbionts.
  • We are very proud of these achievements, and plan to continue our efforts in 2023!