Coral Spawning in the Maldives
Reefscapers Coral Spawning Reports, 2013 onwards
Reef-building corals can reproduce both asexually (via fragmentation) and sexually (via ‘brooding’ or ‘broadcast’). Hermaphroditic broadcast coral species (such as the Acroporidae) reproduce by releasing bundles of gametes (eggs and sperm). These bundles contain fatty lipids and are therefore buoyant, allowing them to travel to the surface of the water column where fertilisation takes place.
This spawning cycle is one of nature’s most spectacular events and only occurs once or twice each year, on cues from water temperature, wind speed and the lunar cycle. A rapid increase in water temperature has been shown as a predictor in coral spawning as it helps mature gametes. Wind speed, notably low wind speed, has also been shown as an indicator to optimise fertilisation.
Coral species are sessile organisms that must synchronise their gamete release to increase chances of fertilisation (gametes only survive for a few hours). Mature colonies develop gametes within their tissues over several months in a process known as gametogenesis, a timely process that utilises a substantial amount of energy and is likely why they only spawn once a year.
This phenomenon has been well-documented around the world (Australia, the Caribbean), however, there is little documentation from the Maldives about species-specific spawning and time of year. It is imperative that we begin to understand synchrony and timing of spawning here in the Maldives, with important implications for the management of coral reef ecosystems and identifying the health of reefs.
Insights into Coral Spawning Patterns on Maldivian Reef Ecosystems
Insights into Coral Spawning Patterns on Maldivian Reef Ecosystems 
These preliminary findings may be subject to change. None should be cited without prior written permission from the authors.
Insights into Coral Spawning Patterns on Maldivian Reef Ecosystems
Introduction
Understanding coral reproduction timings is crucial to expand our knowledge of populations and communities, particularly through recruitment rates and ecosystem connectivity, with important implications on coral reef management and conservation.
Little research has been published on coral spawning synchronicity in the Maldives, despite being the world’s seventh largest reef ecosystem (3% of global reefs). This hinders our understanding of coral reproductive biology at a regional scale, and limits our ability to assess shifts in reproductive phenology over time.
Method & 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) and Kuda Huraa (Kaafu Atoll), and partnered with our colleagues at 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 differences in the day of species spawning is (highly) significant between atolls in both Spring and Autumn. For both seasons, Kaafu Atoll spawns before Baa Atoll, due to different environmental conditions at each latitude: low tide, wind speed, and tidal depth.
Spawning in Kaafu and Baa Atolls – the number of coral colonies per species:
During Autumn 2021
During Spring 2022
Key Findings
- Observed coral spawnings: 18 species of Acroporidae, one species of Goniastrea.
- Two spawning cycles occur each year, during spring and autumn.
- We observed multi-specific synchronous spawning and split spawning.
- Kaafu Atoll coral species typically spawn before species in Baa Atoll.
- Environmental cues identified that coincide with spawning windows.
- Species spawning variation across atolls and seasons.
Future Implications
Coral bleaching decreases reproductive potential of survivors, reduces gamete numbers, and leads to a long-term impact on reproduction over multiple spawning periods. As the persistence of Maldivian reef ecosystems relies on natural recruitment through reproduction, it is imperative to 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.
🪸 Coral spawning patterns of Acropora across two Maldivian reef ecosystems 🪸
Our Reefscapers published research paper: 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.
Conclusions
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.
