Great Barrier Reef Coral Spawning Guide

The outer Great Barrier Reef is home to so many fish and coral species – they come in all shapes, sizes and colours! Here’s a guide to some of the colourful and quirky creatures you might meet on your day trip or overnight trip.

What Is Coral?

Coral is not a plant but an animal, since they do not produce their own food like plants do. Most coral structures are built up of hundreds to thousands of microscopic coral animals called polyps. Each soft-bodied polyp secretes a hard outer skeleton of limestone (calcium carbonate) that clings to either rock or the dead skeletons of other polyps. Corals have small tentacle-like arms that they employ to grab food from the water and scoop it into their ‘’mouths’’.

What Is Coral Spawning?

This mass reproduction of coral occurs just once a year. It includes coral polyp colonies and species releasing microscopic egg and sperm bundles into the water from their stomach cavity at the same time. These bundles then gradually climb to the surface, where the fertilisation process begins. If fertilisation is successful, the fertilised eggs will settle on the ocean floor and eventually grow into coral. The coral boosts the probability of fertilisation by discharging both eggs and sperm at the same time.

When does the coral spawning happen?

To be frank, no one exactly knows! Every year, the spawning occurs within a week of the November full moon but using tests and measures, scientists can predict when it is going to occur during a timeframe of a few days. One reliable factor is that the coral spawning does happen at night, when all plankton feeders are sleeping, allowing eggs more time to settle into the protection of the Reef and increasing their chances of survival.

How do we know when it’s going to happen?

The time of year at which corals spawn is determined by their location. Inshore reefs typically begin spawning one to six nights following the first full moon in November, whereas outer reefs spawn later. Several environmental conditions influence when corals are likely to spawn:

  • For the eggs to develop, the water temperature must be at or above 26 degrees Celsius for at least a month.
  • When there is less tidal action, the coral will reproduce three to six nights following the full moon in November or December (in the northern Reef).
  • The length of the day and salt levels also appear to be variables in determining when the spawning will occur.
  • Short-term control of the coral getting ready to spawn is reliant on lunar cues and the sunset determines the ultimate release, or spawn.

Why does the coral all spawn at once?

Spawning is a mass coordinated phenomenon because male and female corals cannot migrate into reproductive contact with each other, so the timing of a broadcast spawning event is critical to success.

Does the coral spawning happen on the same night across the whole Great Barrier Reef?

No, the coral on the Great Barrier Reef does not all spawn at exactly the same time. The time at which corals spawn is determined by their location. Inshore reefs typically begin spawning one to six nights following the first full moon in November, whereas outer reefs spawn later.

How Can I See the Coral Spawning?

The best way to see the coral spawning is with Divers Den! We offer evening snorkel and dive trips specifically to see the coral spawning. For 2023 these dates are Friday 3rd November, Saturday 2nd December and Sunday 3nd of December 2023. The trip includes dinner and refreshments to refuel you after your time in the water.

Do I need to be a diver to see the Coral Spawning?

No, you do not have to be a certified diver to join a Divers Den coral spawning evening trip. The expedition is open to those who can snorkel, and Divers Den even offers guided snorkel sessions during the trip.

What does it feel like to swim in all the coral spawn?

TThe idea of swimming in a sea of coral sperm might sound weird, but it’s just how Mother Nature works her wonders! The eggs may stick to your skin, hair and wetsuit, and you may feel a bit slimy afterwards, but can be easily washed off with a hot water shower (which are available on board the vessel during our coral spawning tours!).

Does it smell?

It does! Our Course Director Charlotte describes its smell like salty seaweed. Some have also said it smells like the ocean, so not too different to an ordinary night on the Reef!