Multi-specific coral spawning and monsoonal transitions: assemblage-level observations from Baa Atoll, Maldives

Abstract

Coral reefs support a vast diversity of marine life but are increasingly threatened by anthropogenic activities. To assess changes in community composition and the recovery potential of coral reefs in a changing climate, documenting sexual reproduction and understanding its environmental drivers are essential.

Here, we report the exact timing and reproductive strategies for 375 individual coral colonies across 28 species from 10 genera between February 2024 and April 2025 at a near-shore reef in Baa Atoll, Maldives. We identify two peak periods of multi-specific spawning, coinciding with the monsoonal transition seasons. We note variations in spawning patterns within and between taxa, documenting the occurrence of extended breeding via asynchronous spawning of colonies within a species and split-spawning of individual colonies across lunar months and bi-annual seasons. Our results show that larger spawning events in a given month are significantly correlated with lower wind speeds, higher sea surface temperatures, and higher levels of solar insolation.

These findings highlight the influence of environmental cues on the timing and extent of coral reproduction and provide the first detailed spawning records for several non-Acropora genera in the Maldives, contributing a critical baseline for future research.

Conclusion

This study provides new insights into the timing, synchrony, and species-specific patterns of coral spawning in the Maldives, offering the first detailed records for several non-Acropora genera in this region. We found that larger spawning events in a given month were significantly correlated with lower wind speeds, higher sea surface temperatures, and increased solar insolation, highlighting the influence of environmental conditions on both the occurrence and extent of coral reproduction. Because more frequent and severe bleaching events can damage the reproductive fitness of corals, studying the successful reproduction and recruitment of surviving colonies is central to maintaining coral populations and restoring reef structure and function.

Understanding when and how corals reproduce is critical for evaluating the potential of coral populations to recover following disturbance. With restoration initiatives in the Maldives increasingly utilising sexual reproduction (e.g. larval propagation and assisted fertilisation), these findings serve as an important baseline for reef managers, researchers, and restoration practitioners. However, as this study is based on a single year of observations from one atoll, caution must be taken in extrapolating trends across space and time. Long-term, region-wide monitoring is needed to identify the environmental drivers of coral spawning and assess how spawning patterns may shift under future climate scenarios.

Synchrony on the reef: how environmental factors shape coral spawning patterns in Acropora corals in the Maldives

Sheridan K, Monfared MAA, Dixon SP, Errington AJF, Le Berre T. 2025. Synchrony on the reef: how environmental factors shape coral spawning patterns in Acropora corals in the Maldives. PeerJ 13:e19447 – https://doi.org/10.7717/peerj.19447

Key Findings

Over three years, the team at Reefscapers (Kate Sheridan, Margaux Monfared, Simon Dixon, Amelia Errington & Thomas Le Berre) monitored 3,026 colonies across 24 Acropora species in North Malé and Baa Atolls—uncovering the complex environmental cues that drive one of the ocean’s most extraordinary events: mass coral spawning.
As coral conservation increasingly turns to in-situ larval settlement and nature-based interventions, being able to predict when and how corals spawn is more important than ever—especially following the severe bleaching that hit Maldivian reefs during the ongoing fourth global bleaching event.

Key findings:

📈 Temperature: Rising sea surface temperatures don’t predict when spawning starts—but once underway, they do influence how many corals spawn and how synchronized they are.
🌕 Lunar cycles & tides: Most spawning events clustered around the full moon, coinciding with lower tide depths—suggesting that moonlight and tidal forces work together to cue reproduction.
🌧️ Rainfall: Daily precipitation showed surprising correlations with spawning in some species—highlighting the importance of localized strategies.
🧬 Species-specific responses: Even closely related corals reacted differently to the same environmental factors—critical insights for restoration planning.
📚 These findings offer vital guidance for reef managers, restoration practitioners, and policymakers seeking to future-proof coral ecosystems against climate change.

Coral spawning patterns of Acropora across two Maldivian reef ecosystems

Monfared MAA, Sheridan K, Dixon SP, Gledhill M, Le Berre T. 2023. Coral spawning patterns of Acropora across two Maldivian reef ecosystems.
PeerJ 11:e16315 https://doi.org/10.7717/peerj.16315

Abstract

Understanding patterns in coral reproductive biology at local and regional scales is crucial to elucidate our knowledge of characteristics that regulate populations and communities. The lack of published data on coral spawning patterns in the Maldives hinders our understanding of coral reproductive biology and limits our ability to assess shifts in reproductive phenology over time.

Here we document baseline environmental cues, spawning patterns, exact timings and oocyte development of restored and wild Acropora, inhabiting shallow water reefs, across two Maldivian atolls. A total of 1,200 colonies were recorded spawning across the two sites between October 2021 and April 2023. These colonies represent 22 species of Acropora, with coral spawning observed over an extended period of eight months. This research details exact spawning times of multi-specific spawning, asynchronous spawning and ‘split spawning’ of Acropora, across multiple lunar phases; and highlights the need to consider restored colonies when discussing the sexual reproductive patterns of Maldivian Acropora in the future.

Overall, corals spawned earlier in North Male Atoll compared with Baa Atoll. Earlier spawning events were significantly correlated with lower tide depths, wind speeds, daily precipitation and higher sea surface temperatures which helped explain inter-atoll, inter-annual, and intra-annual variations in spawning day. This study contributes to understanding sexual reproductive cycles of Acropora in the Maldives; knowledge that is vital for effective management of a critically endangered ecosystem in a changing climate.

Stages of sexual reproduction in Acropora, Maldives.

(A–C) Development of oocyte colouration from white (immature; (A)), to pale (B), to pigmented (mature; (C)) in A. millepora. These classifications were used to inform field monitoring for spawning. Photographs by Margaux A.A. Monfared.
(D) Observed gamete ‘setting’ in A. secale prior to spawning. The presence of ‘setting’ as shown in this image is what observers were looking for during nightly surveys. Photograph by Kate Sheridan.
(E) Photograph to show moment of gamete bundle release in A. rosaria, defined as the spawning time per colony. Photograph by Simon P. Dixon.
(F) A colony of A. gemmifera spawning egg-sperm bundles. In situ observations suggested these oocytes were white-pale. Photograph by Kate Sheridan.

Conclusion

Our research details for the first-time exact spawning times of Acropora across two Maldivian atolls elucidating patterns of multi-specific spawning, asynchronous spawning and ‘split spawning’ across multiple lunar phases.

It is clear the Maldives experiences two distinct spawning seasons throughout the year, but spawning events can occur over an extended period of eight months.

Inter-atoll variations in spawning day are likely influenced by local environmental factors, however further research into coral reproductive patterns of multiple study sites within atolls and across the Maldives needs to be conducted to ascertain regional disparities and seasonal variations.

The preliminary findings of spawning patterns based on reef type in this study demonstrate the need to consider restored colonies when discussing the sexual reproductive patterns of Maldivian Acropora in the future.

Insights into Coral Spawning Patterns on Maldivian Reef Ecosystems

Introduction

Methodology & Results

We examined baseline environmental cues, spawning patterns, timings and gametogenic cycles of Acroporidae in naturally occurring wild colonies and asexually propagated restored colonies. We analysed shallow water reefs across Landaa Giraavaru (Baa Atoll), Kuda Huraa (Kaafu Atoll), and Sheraton Full Moon (Kaafu Atoll).

Differences in tide height across 4 days in November 2021, with time of spawning overlayed for 3 species of Acroporidae in Baa atoll.

The difference in day of species spawning is highly significant between atolls in Autumn (p<0.001) and significantly different in Spring (p<0.05). For both seasons Kaafu Atoll spawns before Baa Atoll. This is linked to significantly different environmental conditions at each latitude: low tide (p<0.001), wind speed (p<0.0) and tidal depth (p<0.001).

Key Findings & Future Implications

• • 18 species of Acroporidae observed spawning and one species of Goniastrea
  • Two spawning cycles occur each year during spring and autumn
  • Multi-specific synchronous spawning and split spawning observed
  • Kaafu Atoll coral species typically spawn before Baa Atoll
  • Environmental cues identified that coincide with spawning windows
  • Species spawning variation across atolls and seasons

Coral bleaching decreases reproductive potential of survivors (Leinbach et al., 2021), reduces gamete numbers (Ward, Harrison & Hoegh-guldberg, 2002) and leads to a long-term impact on reproduction over multiple spawning periods (Levitan et al., 2014).
As the persistence of Maldivian reef ecosystems rely on natural recruitment through reproduction, it is imperative we understand reproductive rates to predict population recovery following disturbance. This information will help us to understand regional spawning patterns and shifts in reproductive phenology over time.

Researchers: Margaux Monfared, Simon Dixon, Amelie Carraut, Kate Sheridan, Matthew Gledhill, Thomas Le Berre & Alejandra Woolrich

Acknowledgements: Thanks to the whole Reefscapers team, and to our Resort colleagues at both Four Seasons and Sheraton for their support.