Genetic diversity is unfortunately rarely taken into account in reef restoration projects. Our Reef Conservation Program has just completed its third year of a new type of coral restoration process that focuses specifically on increasing the amount of diversity on the coral reef. This process is called coral larvae culturing, and is a newly developing technique for use in local and community based reef management programs such as ours.
The process utilizes the natural phenomenon known as mass coral spawning, whereby corals across the reef synchronously release egg and sperm bundles into the water column. These bundles then burst, allowing the eggs and sperm from different colonies to interact and fertilize, leading to the development of coral larvae. These larvae then travel through the ocean for a few days, and then settle down to create new coral colonies. Through this reproductive strategy, corals are able to spread to new areas, regrow areas that have been disturbed, and adapt to changing environments over successive generations.
This strategy of reproduction has worked for about 240 million years in hard corals, but it is not necessarily efficient, and coupled with reef threats and climate change, recruitment on many reefs cannot keep up with mortality rates. There are many examples as to why corals would fail to successfully reproduce due to the reef decline being experienced globally, such as; adult colonies are too far apart or too few to successfully fertilize, water quality is too low or pollution negatively affects the unprotected coral larvae, larvae are brought away from reefs during storm events, there is not good substrate available on the reef for the larvae to settle onto, or conditions are so bad that the settled larvae cannot survive. However, due to the fact that corals release millions of eggs into the water during spawning events, there is a lot of room for reef managers to positively intervene in the process.
Our coral larvae culturing program is focused on increasing coral recruitment on our reefs and also providing us with corals to use in restoration projects that are all genetic individuals with differing traits. We do this by going out to collect gametes (eggs and sperm) from the spawning corals across the reefs, and then fertilizing them in buckets on the boat. We then rear the larvae in our culturing center tanks for about 1 week, ensuring that they have all of the requirements they need to successfully survive. This is in very different from conventional coral restoration techniques in a number of ways.
Most coral restoration projects are use the process of propagating and transplanting corals, this means they break up or find broken coral colonies, let them grow, and move them to the restoration area. This process does have many benefits and is an important tool for any reef manager, but it also has some major drawbacks. One of the biggest ones is that it does not actually increase the genetic diversity on the reef, since all the corals created are clones of each other. This has the effect of leading to reefs that are not resilient, meaning they will not too well when a major problem occurs, or will struggle to come back from that problem.
Coral culturing projects not only increase the genetic diversity of the corals in a reef, but they can aid in the adaptation of reefs to climate change by reducing generation times, increasing the available genetic material for future reefs, breeding high fitness corals through cross-fertilization or hybridization, and more.
The possibilities of coral larvae culturing for restoration are only now being realized as this field develops, and we are proud to be a part of this movement. You can find out more about our corals spawning activities on our coral spawning page or facebook group. If you would like to receive training in these techniques and assist us a coral culturing project you can sign up for one of our marine conservation courses.
You can also check out our youtube films on coral spawning:
Coral Spawning 2012, Koh Tao Thailand