My niece is at the age where she’s asking lots and lots of questions. She’s especially interested in learning about how different animal young are born. She recently asked me about baby fish and I’ll admit I was stumped. So I had to do some research to answer her questions. I love it when she thinks of these great questions! Taking that line of questioning into account, I decided that the next section for my coloring book should be all about coral babies would be a fun thing to learn – for me as well as my niece!
Learn About the Coral Life Cycle
Coral can reproduce two different ways; they can clone themselves by creating an exact duplicate of themselves or they can produce eggs and sperm and reproduce sexually. Most of the year, coral grows by creating copies of polyps. This is advantageous for the coral because as long as there are at least a few polyps, it can always keep growing. When we plant coral to restore the reefs, we rely on that cloning ability by taking tiny pieces of coral and protecting it in nurseries until it is big enough to be planted out on the reef. The pieces are secured to the ground and then left to keep growing into a big healthy reef.
Coral also undergoes a reproductive cycle called sexual reproduction. This is very important because while a clone is an identical copy, a new baby coral has unique DNA. Scientists use this to help grow coral that are stronger and better able to survive in places where all the other coral have died.
The reproductive cycle of coral is pretty amazing. Coral are Broadcast Spawners – this means they release their eggs and sperm into the ocean where they float around and mix together, then the fertilized eggs begin their journey to become new baby coral.
Releasing Gamete Bundles
Once a year, coral releases their gamete bundles in one amazing synchronized event. It always happens at night after a full moon in the summer when the warm temperatures have signaled to the coral that it’s time. The whole event can last a few days up to a week because different species of coral release their gametes on different days. The gamete bundles are a mix of eggs and sperm that float to the surface and then break apart so all the eggs and sperm can mix together at the surface. This is how the coral eggs get fertilized.
Fertilization and Development
Just a few hours after fertilization, the fertilized eggs begin to divide and develop into a coral embryo. There are fun names for the different stages of embryo development like Morula and Prawn Chip. The final stage of embryo development is called Gastrula. Finally, the embryo becomes a planula larva. A Planula larva is a free-swimming larva that can swim with tiny little hairs all over its body called cilia. The cilia aren’t very effective at moving the larva so it tends to get swept along by water and wind currents. A coral larval floats around on the surface for days or even months while it looks for the perfect spot to make their home. This is also when it may start to collect its symbiotic partner, zooxanthellae.
Settlement and Growing
When it’s ready, a mature larva will sink into the ocean and attach itself on the ocean floor. Once it settles on a surface or substrate, it becomes totally stationary and will grow in that spot for the rest of its life. Once it is attached to a surface, the larva begins its stages of metamorphosis in order to transform into a polyp. The polyp will then grow, and make copies of itself through cloning in order to create its new colony. Like most living organisms, corals take a few years or more before they begin to reproduce.
- Humann, P., DeLoach, N., & Wilk, L. (2013). Reef coral identification: Florida, Caribbean, Bahamas.
- Zooxanthellae … what’s that? Corals Tutorial. National Ocean Service, NOAA. https://oceanservice.noaa.gov/education/tutorial_corals/coral02_zooxanthellae.html
- What is the life cycle of coral? (slideshow) https://encounteredu.com/multimedia/images/what-is-the-life-cycle-of-coral