Every year, in the stillness of the ocean here in Bali and under the glow of the full moon, coral reefs enter one of the most important phases of their life cycle: spawning. It is not merely a biological event, but a natural spectacle that occurs only a few times a year—when corals release millions of new lives into the sea, triggered by the lunar cycle. A phenomenon that not only marks the birth of a new coral generation but also brings hope for reef ecosystem restoration as this sexual reproduction preserves genetic diversity and allows reefs to be more resilient to future threats.
The year 2025 was a particularly meaningful one for me at Ocean Gardener, as it was the first time I took part in monitoring coral spawning at the Mero site in Tulamben. In 2025, Ocean Gardener carried out intensive coral spawning monitoring programs across Tulamben, Nusa Penida, and Pemuteran.
Why Is Coral Spawning Monitoring So Important?
Coral spawning is the foundation of reef regeneration. Without healthy and synchronized gamete release, the chances of larvae becoming fertilized and successfully settling as new coral colonies are extremely low. Through monitoring, we can understand when and how corals spawn, and use that data to support larval-based restoration or assisted sexual reproduction (where scientists better the odds of larvae survival by raising baby corals in the labs). Think of in-vitro fertilization, but for corals. This is one of the key strategies in coral reef conservation today.
The Beginning of the Journey: Preparations Before Spawning
Long before those nights arrived, our journey had already begun. The Ocean Gardener team conducted a series of workshops and training sessions, both online and offline in various locations. We used data on full moons, sunset times, and spawning records from previous years to estimate when the spawning peak would occur. We learned how to read “setting” signs, identify coral gametes, and install funnel traps above coral colonies without damaging their structures. We also practiced how to use nets to collect gametes at night — when the only light on the seafloor comes from our dive lamps.
These workshops became the scientific foundation for everything that followed.
The Monitoring Days: From Light to Darkness
Coral reef monitoring lasted approximately ten days. The first day began two days before the full moon phase, with the installation of twenty funnels on various corals: Acropora, Montipora, Platygyra, Goniastrea, Duncanopsammia, Turbinaria, and several other genera. Each following day, we dove again to check, adjust, or replace any funnel that had detached. Currents shifted, visibility fluctuated, yet the rhythm of diving felt almost like a ritual — descend, check, record, and resurface with the same curiosity that never seemed to fade.
During the daytime, the sea of Tulamben felt welcoming — bright, clear, and full of small life. But nighttime brought forth an entirely different world.
Night dives began three days after the full moon. When the spawning peak nights approached, divers get ready 30 minutes after sunset and get in the water 60 minutes after sunset, searching for the first signs of “setting” and preparing to deploy the nets over egg-filled colonies, and monitoring other colonies.
No Gametes in Amed, but Many Lessons
By the final day of monitoring — even after the last funnel was removed — not a single trap contained eggs or sperm. Scientifically, this was not a disappointing result. Instead, it provided clear insight that the corals in Mero did not spawn during this period, or they spawned in a very short window or in locations our funnels did not cover.
The absence of detectable spawning in Tulamben this year is a significant finding that strengthens the long-term monitoring baseline and contributes to a clearer understanding of coral reproductive dynamics at this site.
Such results are crucial for long-term spawning pattern mapping. Corals do not always spawn in the same month each year, even when the lunar phase or environmental conditions appear favorable. Temperature changes, prior weather conditions, or certain stress factors may have influenced the reproductive timing this season.
Even without witnessing spawning firsthand, I felt an even deeper connection to the process. Monitoring is not just about results — it’s about understanding that corals move to rhythms far more subtle than what we expect.
Coral Spawning In Pemuteran, Bali
Although there was no spawning in Tulamben, we are happy to report that the corals in Pemuteran, Bali spawned as scheduled! Plenty of Porites cylindrica, Porites lobata and a few Acropora like this Acropora humilis last night.
Thanks to Easy Divers for being our coral spawning monitoring partners in Pemuteran.
Inviting More People to Become Part of the Story
Coral spawning is a story of hope — of the beginning of new life that happens only a few nights each year. Our team descended into the dark, waiting for signs that sometimes appeared, sometimes not. But when they did appear, they reminded us why this work is so important. Whether a night resulted in spawning or not, every observation adds to our understanding of coral biology, coral spawning timing, and potentially how we can use this data for future coral restoration efforts.
The essential work of observing and recording the natural cycles of coral reefs remains critical. Crucially, the good news comes from our partners in Pemuteran, Bali, where the corals did spawn according to the predicted timeline. As long as these precious corals are reproducing successfully in nearby locations, the genetic diversity of the region is preserved.
This successful spawning offers a profound source of hope, as a large and varied gene pool increases the chance that some offspring will possess resilient traits capable of better resisting diseases, warming waters, and other environmental challenges. We will continue our monitoring, fueled by the success of our Pemuteran colleagues and the deep commitment to protecting these precious reefs of Bali.
Are you dive shop or resort that is interested in partnering with us to monitor spawning or build more coral nurseries, don’t hesitate to reach out to us.
