Interesting mass spawning facts:
- This spectacular event was only first described by scientists in 1984. The phenomena was observed on the central Great Barrier Reef and has since been observed in other countries at other times of year. The team responsible was awarded the Eureka Prize for Environmental Research in 1992.
- Scientists once assumed that coral colonies picked up sperm in the water and fertilised eggs internally. Since the discovery of mass spawning, it is now realised that for many corals fertilisation takes place in the water.
- Most corals are hermaphrodites! Being both male and female, they have both egg and sperm which are released in small bundles which float to the surface, hopefully allowing eggs and sperm to get together.
- Synchronised spawning of many coral species is thought to help prevent everything being eaten up by predators like fish – there is simply too much coral spawn at the same time for all to be eaten.
- The timing for mass spawning on the reef can be predicted, taking into account water temperatures, moon phases and possibly factors such as day length and salinity. A few nights after the full moon in November is a good guess. Cues for the mass spawning are sensed by the corals through photoreceptors, plus a chemical that allows them to ‘smell’ each other spawning.
- Mass spawning does not happen on the entire reef at once. Inshore reefs usually start one to six nights after the first full moon in October, whereas those in outer reefs spawn during November or December.
- Soft corals usually spawn before the hard corals, and the spawning can go on for several nights.
- Sometimes over 100 species of corals can be observed spawning on the same night.
- Spawning can be replicated in aquarium settings, which provide unique opportunities to researchers. The Australian Institute of Marine Science’s (AIMS) has a ‘Sea Simulator’ where large numbers of coral larvae are produced for scientific experiments.
- Early indications are that 2019 could be a bumper year, with large volumes of coral egg and sperm creating what looks like an underwater snowstorm!
Images Katie Chartrand-Miller