Coral Spawning — The Ocean's Greatest Event
Quick Fact
During coral spawning, a single reef can release billions of egg-sperm bundles in a single night — the ocean turns pink with the density of reproductive material.
About This Species
Once a year, triggered by the full moon and rising water temperatures, coral reefs around the world release billions of eggs and sperm bundles simultaneously in a spectacular mass spawning event. The synchronisation is extraordinary — entire reef systems spawn within the same few hours, maximising the chance of fertilisation. The fertilised eggs develop into free-swimming larvae that drift in the plankton before settling on the reef and growing into new coral polyps. Coral spawning is essential for reef recovery and genetic diversity.
Why It Matters
Coral spawning is the primary mechanism by which reefs recover from bleaching events and physical damage. Rising ocean temperatures are disrupting spawning cues, threatening the reef's ability to regenerate.
Transcript
Once a year, on a night determined by the full moon and rising water temperatures, something extraordinary happens on coral reefs around the world. The corals spawn. Millions of coral polyps — across an entire reef system, sometimes spanning hundreds of kilometres — simultaneously release tiny bundles of eggs and sperm into the water. The ocean turns pink and white with the density of reproductive material. It looks like an underwater snowstorm in reverse. The synchronisation is one of nature's most remarkable feats of coordination. Corals have no nervous system, no brain, no way of communicating with each other. Yet they respond to the same environmental cues — water temperature, lunar cycle, day length — and spawn within the same few hours. The mass release maximises the chance that eggs and sperm from different coral colonies will meet and fertilise. The fertilised eggs develop into free-swimming larvae called planulae, which drift in the plankton for days or weeks before settling on the reef and growing into new coral polyps. This is how reefs recover from bleaching events and physical damage. This is how genetic diversity is maintained across vast distances. But coral spawning is being disrupted. Rising ocean temperatures are shifting the timing of spawning events, decoupling them from the lunar cycles that trigger them. Bleached and dying corals don't spawn at all. I've been fortunate enough to witness coral spawning. It's one of the most beautiful things I've ever seen in the ocean. And one of the most fragile.