CORAL SPAWNING AND LARVAL CULTURING

Corals reproduce through a mechanism known as coral 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 water's surface and are fertilized. 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, but this is also where the next generation of corals will come from. Each coral larvae that settles successfully is called a coral recruit, and is a genetically distict individual. These recruits replenish the reefs with new individuals, and increase the reefs diversity and ability to adapt to changes.

What we are doing

In our Coral Spawning and Larval Culturing Program, we go out and observe document this event, and simultaneously collect the gametes (eggs and sperm) which are brought back to our nursery. From here, they develop as larvae for several days, then are settled onto artificial substrates, a sort of concrete mushroom. We then take care of the juvenile corals 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 with unqie, and possibly better adapted corals.

Why Coral Spawning

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.

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 bottlenecking 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.

The larval culturing process

The process of coral larval culturing is a slow and laborious. Once a coral's gametes have been fertilized, they enter the free-floating planktonic phase of their life cycle as a planula. These near microscopic planula take several weeks to metamorphize and settle onto the seafloor, or in the case of our larval culturing program, small concrete molds that we've covered in the chemical cues that encourage the coral larvae to recruit to them.

Once the larvae have settled to these concrete molds they're often too small to observe with the naked eye, so a microscope is necessary to find out when they've done so. After we've confirmed that they've entered the polyp stage of their life cycle, we can then transplant the concrete molds out onto one of our artificial nurseries, where our little "coral babies" can grow in optimal conditions. After a couple of years, depending on the genus of coral, they'll be roughly the size of a golf ball, and not long after that will they be ready for transplantation to their final resting place, where they'll continue to thrive and grow into healthy, genetically unique colonies that will help spawn the next generation of beautiful corals.

Pictured here are several colonies of Goniastrea edwardsi that were cultured from one of the first efforts of our Larval Culturing Program.

How to get invovled

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.

See some of our papers and reports relevant to coral spawning

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