Coral Spawning 1 Coral Spawning 2 Coral Spawning 3

Coral Spawning

Corals cannot move around to find mates, but instead reproduce through a technique known as spawning. In coral spawning, all of the corals from one species will release their eggs and sperm into the water over about 15 minutes, which rise to the surface and fertilize.  This event, which usually happens just once a year for most corals, is one of the most amazing and miraculous events in all of nature. Not only is it amazing that corals can all time this event without having a brain or any means of communication, this is also where the next generation of corals will come from. Each coral that settles successfully is called a coral recruit, and is a distinct individual genetically. These recruits replace any adults that die, and also help to keep corals adapting to changing conditions in the planet’s oceans.

In our Coral Spawning and Larval Rearing Project, we go out and observe this event, and then collect eggs and sperm to stock out culturing ponds with larvae. We then take care of the larvae for several years, until they are big enough to be transplanted to the natural reef or artificial reefs as part of our different restoration programs. Most coral restoration programs  focus on the asexual reproduction (cloning) of corals, but we are working on methods to increase the availability or using coral spawning capture and rearing to restore damaged reef areas.


Goneastrea coral spawning

A goniastrea coral releases egg and sperm bundles into the water in Chalok Ban Kao, Koh Tao, 2012.

Did you know that Charles Darwin is actually attributed with being the world’s first coral restorationist? He discovered that a broken coral rolling around in the sand would usually die, but by securing that coral to a piece of bamboo driven into the sand it could be saved. In the 150 years since, coral restoration has not come that much further – the materials and techniques have evolved, but the concept is still mostly the same: securing broken pieces or corals so they can regrow.


In fact, most programs around the world use what they call ‘donor corals’ to create feedstocks for their nurseries and restoration work. This means they select healthy corals from the reef, break them up into hundreds of pieces, and then grow new colonies from those pieces (cloning corals). Short term success is usually very high when this method is used, it is easy to get new coral colonies to grow from the fragments.


coral eggs

The red bundles in this cross section of Goniastrea are the egg and sperm bundles, almost ready for release after the full moon

Unfortunately, most of these projects overlook the problems with diversity created by filling reefs with cloned colonies. Some inherent problems include:

  • Reduced species diversity (reduced habitat diversity for other animals)
  • Genetic bottle necking or founder effects
  • Inbreeding or the inability to breed (coral cannot ‘self’ or reproduce with other colonies that have the exact same DNA)
  • Reduced ability to adapt to climate change
  • Reduced Reef Resilience (the ability of the reef to withstand or rebound from disturbances)

Due to these problems the long-term success of these projects are often low, and in some cases leads to reduced health, abundance, or diversity of the coral populations and reefs.


Since 2010, we have been developing this program alongside the Prince of Songkla University (Hat Yai), with the hopes that one day most of our feedstocks for restoration are derived from larval culturing projects.  This allows us to create feedstocks for restoration that are all genetic individuals. With these techniques we hope to increase our long term success and create more resilient reefs around our island that will better adapt to changes in our local and global climate.


Students in our program learn about coral life cycles, taking a genetic approach to coral restoration, coral spawning timing, gamete collection, and coral larvae culturing. Twice a year (around February and March) we dive to observe coral spawning and capture coral eggs and sperm for our selective breeding program. These gametes are then cross fertilized, reared up in tanks on land, and then transplanted back to the local reefs. Furthermore, we are developing a manual to teach other local or community based managers how to implement the same techniques in their areas to increase the long-term success of their coral restoration efforts.


Check out the links below to learn more about our spawning programs:

– Coral Spawning and Larval Culturing Programs for Reef Restoration

– ‘A Coral’s Journey,’ A Documentary by Alex Aubert

– The Magic of Coral Spawning, 2014

– Coral Reef Restoration for Increased Genetic Diversity


Volunteers Look after the coral embryos in 2010

Volunteers Look after the coral embryos in 2010

Coral Gametes are fertilized in buckets on the boat

Coral Gametes are fertilized in buckets on the boat

A 2.5 year old colony of goneastrea growing on aritficial substrates from our 2010 project

A 2.5 year old colony of goneastrea growing on artificial substrates from our 2010 project

A colony of Goneastrea growing on the artificial substrate

An 11 month old colony of Goneastrea growing on the artificial substrate from our 2012 project

Contact Us Button