Coral Spawning and Larval Culturing on Koh Tao
It was another successful year of coral spawning and larval culturing on Koh Tao, our 9th successful season since we started this project in 2010 with the Prince of Songkla University, Hat Yai. This year was extraordinary for the number of corals that successfully released their gametes, with our team observing species from 9 different genera going over the 3 nights of observation in March. And, for the first time on Koh Tao, we also observed a species of soft coral (Sinularia) releasing their egg bundles. This miraculous event happens only a few times per year, and we are increasingly able to be there at the right time and place, and equipped with the knowledge and skills to help improve their reproductive success.
What does our team do during spawning?
This year, we collected gametes (eggs and sperm) from several genera of coral including Goniastrea, Platygyra, and Cyphastrea.. The gametes are collected from the corals in three different locations as they are released, using butterfly nets. From there, they are transferred to bottles while underwater, and then brought to the boat for fertilization. On the boat, the eggs and sperm are combined in several mixing tubs, this not only increase the fertilization rate several-fold over natural conditions, but also protects them from predation. Furthermore, they are fertilized according to our selective breeding matrix to increase the likelihood of intraspecific hybridization, increase genetic diversity, and reducing founder effects or genetic bottlenecking.
After fertilization, the eggs are transferred to our culturing tanks on land to develop into embryos and eventually swimming coral larvae. After about a week and half, the larvae will be fully developed and ready to settle down. At that point, our team places pre-conditioned settlement plugs into the culturing tanks and uses special chemical cues to trick the corals into thinking they are on a coral reef. From there the plugs are transferred to our mid-water nurseries to grow and mature before being outplanted to the natural reef or our artificial reef structures.
Why is this better than propagating or ‘fragging’ coral?
By using coral larvae, we are creating a feedstock of coral on our nurseries which are each genetic individuals. This means that each coral colony is uniquely adapted and have a diversity of physical responses to changes in climate or immunities to disease. This is very different from projects which use fragging (the asexual reproduction of corals through breaking up large colonies into smaller pieces) which creates feedstocks of coral with little to no genetic diversity, much like monocropping on land. Such projects are easy, and can create a lot of daughter colonies for a nursery, but the long-term success of those projects is generally low, and they may even be harming the future of the reef. By reducing the genetic diversity of reef populations, such projects encourage reproductive failures, the spread of disease, mass mortality during disturbance events, and genetic effects such as inbreeding depressions and genetic bottlenecking. All of which leaves reefs less able to adapt to climate change and chronic disturbances caused by human activity.
Do coral spawning projects help corals adapt to climate change?
While fragging programs make corals less adaptive to changes in their environment, the opposite is true of coral spawning projects. First, these projects improve the rate of fertilization and larval survival during the sexual reproduction of the corals, leading to greater reproductive success and higher genetic diversity on restored reefs. Genetic diversity and survival of offspring are the keys to adaptation and evolution, something which normally happens very slowly for long lived species such as corals. Furthermore, our program also uses methods of selective coral breeding in the same way that humans have done with plants and animals in agriculture for hundreds of thousands of years. Our selective breeding program uses the most fit corals and both intra- and inter-specific hybridization to create offspring that may survive better in changing reef environments than their parent populations.
How can I get involved?
Although some corals spawn at various times during the year, the peak spawning seasons on Koh Tao are generally during February-April. If you want to join this exciting program to assist or conduct your own research project please let us know. We are always happy to develop this program further, and currently have many research questions that we hope to investigate over the coming years.