Coral Baby
How do corals make baby corals if they can’t move?
Great question!

Corals may be stuck in place but they have a special way of making babies. It is a phenomenon called coral spawning. Only once a year on carefully timed nights, influenced by temperature, moon cycles, and sunset many coral species release millions of eggs and sperm into the ocean all at once. This synchronised event creates colourful underwater ‘snowstorms’ of reproductive cells. When these gametes (sperm & egg cells) meet in the water, they join to form tiny coral larvae called planulae.

These baby corals float through the ocean, carried by currents, looking for a new place to settle. Some may find a home in just two weeks, while others drift up to two months! But the odds are though – only about 1% of these larvae will actually survive long enough to settle and grow into adult corals.

How do coral larvae decide where to settle?
This is another fascinating part! Coral larvae listen for their new home. Healthy coral reefs are noisy places, full of crackling, popping and other natural sounds made by fish and reef life. Larvae are drawn to these sounds, which help guide them to vibrant, living reefs.

Scientists are now using this knowledge to restore damaged reefs by mimicking these sounds and releasing chemical cues that simulate healthy environments – like creating an irresistible invitation to coral babies.

Corals are very delicate
Corals thrive only within specific temperature, salinity and light ranges. Most reef building corals require:

Water temperature between 23 and 29° C
Clear shallow water for sunlight (they rely on symbiotic algae called zooxanthellae)
Stable salinity
Corals are sensitive to stress. Even slight stress such a s 1 – 2° C rise in temperature can cause coral bleaching, where they expel their algae, turning white.

Most corals grow just a few millimeter to a few centimeters per year. So damage from anchors, pollution, drift nets or storms can take decades to heal.

Odd that coral spawning happens only once a year and that only 1% of the larvae survives.