CORAL SPAWNING
What is Coral Spawning?
Coral spawning is a synchronized reproductive event where corals simultaneously release gametes (eggs and sperm) into the water column. Coral spawning is a precisely timed event that plays a crucial role in the life cycle of coral reefs. The successful fertilization of the gametes that are released leads to the formation of coral larvae, which eventually settle and grow into new coral colonies, thereby ensuring the continuity and genetic diversity of coral populations.
Why is Coral Spawning Important?
Coral reefs are among the most biologically diverse and ecologically significant ecosystems on the planet, and many different species of coral spawn. Coral reefs provide habitat and shelter for approximately 25% of all marine species, despite covering less than 1% of the ocean floor. These vibrant underwater structures also offer critical services, such as coastal protection, sources of food, and livelihoods for millions of people worldwide. However, one of the most remarkable yet lesser-known phenomena contributing to the vitality and regeneration of these ecosystems is coral spawning.
“Based on the World Register of Marine Species (WoRMS), there are currently c. 242,000 known valid marine species living in the world's oceans and marine biota continue to be discovered and named steadily at a current average of 2,332 new species per year.”
Bouchet et al. (2022)
When Do Corals Spawn?
The synchronized reproductive process of coral spawning is influenced by a combination of seasonal patterns, lunar cycles, and various environmental cues. The lunar cycle, particularly the full moon, serves as a natural cue for coral spawning, with moonlight playing a crucial role in triggering these events. Typically, coral spawning occurs once a year, often during late spring or early summer when water temperatures are warmer. This seasonal timing ensures that the conditions are optimal for the survival of the coral larvae.
“Many broadcast spawning corals in multiple reef regions release their gametes with incredible temporal precision just once per year, using the lunar cycle to set the night of spawning. Moonlight, rather than tides or other lunar-regulated processes, is thought to be the proximate factor responsible for linking the night of spawning to the phase of the Moon.”
Brady et al. (2016)
Does Water Temperature Affect Spawning?
Water temperature is another critical factor in triggering coral spawning. Corals are highly sensitive to changes in their environment, and a slight increase in water temperature can signal the onset of the spawning season. Other environmental cues, such as day length and tidal patterns, also play a role in coordinating the timing of these events. For instance, the Great Barrier Reef in Australia experiences mass coral spawning typically in November, a few days after the full moon, when water temperatures have risen sufficiently. Because of this correlation, the effect of climate change and warming seas on coral spawning patterns warrants significant further investigation.
Rapid increases in sea surface temperature are the best predictor for coral mass spawning across large geographical scales, suggesting that spawning is timed for optimal fertilization success.
Keith et al. (2016)
By understanding the mechanics and importance of coral spawning, we can better appreciate the complexities of coral reef ecosystems and the critical need for their conservation amidst growing environmental threats. Check out these great resources to learn more about coral spawning around the world!
REFERENCES AND ADDITIONAL READINGS
https://oceanservice.noaa.gov/education/tutorial_corals/media/supp_coral06d.html
https://www.barrierreef.org/news/explainers/what-is-coral-spawning
Babcock, R., Bull, G., Harrison, P., Heyward, A., Oliver, J., Wallace, C., & Willis, B. (1986). Synchronous spawnings of 105 scleractinian coral species on the Great Barrier Reef. Marine Biology, 90, 379-394. https://doi.org/10.1007/BF00428562.
Boch, C., Ananthasubramaniam, B., Sweeney, A., Doyle, F., & Morse, D. (2011). Effects of Light Dynamics on Coral Spawning Synchrony. The Biological Bulletin, 220, 161 - 173. https://doi.org/10.1086/BBLv220n3p161.
Brady, A., Willis, B., Harder, L., & Vize, P. (2016). Lunar Phase Modulates Circadian Gene Expression Cycles in the Broadcast Spawning Coral Acropora millepora. The Biological Bulletin, 230, 130 - 142. https://doi.org/10.1086/BBLv230n2p130.
Cowen, L., & Putnam, H. (2022). Bioinformatics of Corals: Investigating Heterogeneous Omics Data from Coral Holobionts for Insight into Reef Health and Resilience.. Annual review of biomedical data science. https://doi.org/10.1146/annurev-biodatasci-122120-030732.
Bouchet, P., Decock, W., Lonneville, B., Vanhoorne, B., & Vandepitte, L. (2023). Marine biodiversity discovery: the metrics of new species descriptions. , 10. https://doi.org/10.3389/fmars.2023.929989.
Nozawa, Y. (2012). Annual Variation in the Timing of Coral Spawning in a High-Latitude Environment: Influence of Temperature. The Biological Bulletin, 222, 192 - 202. https://doi.org/10.1086/BBLv222n3p192.
Keith, S., Maynard, J., Edwards, A., Guest, J., Bauman, A., Hooidonk, R., Heron, S., Berumen, M., Bouwmeester, J., Piromvaragorn, S., Rahbek, C., & Baird, A. (2016). Coral mass spawning predicted by rapid seasonal rise in ocean temperature. Proceedings of the Royal Society B: Biological Sciences, 283. https://doi.org/10.1098/rspb.2016.0011.
We welcome observations you would like to share or corrections you might note. Contact us!
Photo credits: Christine Zalewski for Dear Ocean and Unsplash via Squarespace.