How Do Corals Reproduce?
Corals reefs are remarkable environments that comprise of less than 0.1% of the sea floor yet support 25% of all marine life. Corals may appear as lifeless rocks, but they are animals that undertake astonishing cycles of reproduction that have been ensuring the continuation of reef ecosystems for millennia. With the threat of climate change, it is more important than ever to understand the mechanisms of coral reproduction.
Asexual Reproduction
It is easy to confuse corals for plants too, as they “grow” with the sunlight, thanks to a symbiotic algae they have in their tissues that photosynthesise and give the corals sugars and oxygen. Corals use these sugars that the algae provide to asexually reproduce, where the polyps divide and bud to produce more individual polyps that are all genetically identical – expanding the colony’s size. Colonies can also break into fragments from physical disturbances like storms. These fragments can establish new colonies upon settling in a suitable habitat. This is widely taken advantage of in coral restoration as a simple technique to propagate new coral colonies! (read our other blogs for more)
These are the most common forms of asexual reproduction in corals, but they are a very diverse group of animals, and some species have been known to demonstrate some quite unique examples of asexual reproduction. For example, the species Seriatopora hystrix does something called polyp bail-out; when stressed, individual polyps are isolated and detach themselves from their skeleton, falling to a new location that may have more favourable conditions where they can reattach and form a new colony, almost like the last coral lifeboat leaving the sinking ship!
Sexual Reproduction
Sexual reproduction in corals however is something truly spectacular. The primary mechanism for coral reproduction is known as broadcast spawning. One of nature’s most magical events, where millions of coral colonies release their gametes simultaneously. This synchronicity boosts the chances of fertilisation and overwhelms predators with sheer abundance. But how do colonies from thousands of miles away know to release their gametes at the same time??? The answer – environmental cues such as lunar cycles, time of day and water temperature help corals time these events with insane levels of precision.
Once the gametes mix in the water column, the egg and sperm meet, and a planula larva is formed! This is the only time in a corals life cycle that they are able to swim! The planula larvae will seek out a healthy reef based on the sounds it produces and will find a rock or hard substrate to settle on. After a few days, the first coral polyp is born, and asexual reproduction can begin!
Some corals are capable of a method of sexual reproduction known as brooding. Rather than dispersing the gametes into the water column, the fertilisation between the male and female gametes is internal and the planula larvae are released once its internal development is complete.
Species Focus: Porites rus
Here in French Polynesia, we have been participating in the global citizen science project Tama No Te Tairoto (Children of the Reef). This global collective of scientists and coral enthusiasts had more than 400 observers from 21 different countries monitoring the coral Porites rus and its spawning event. Porites rus is a gonochronic species, meaning it has male and female colonies that spawn. The males usually spawn first with the females following suit not long after. This is the first time that Porites rus has been studied at such scale, with spawning observed in both the North and South hemisphere simultaneously! This global synchronization suggests that Porites rus coordinates its spawning over distances exceeding 18,000 km, influenced by environmental cues such as sunrise times.
Why Does Coral Reproduction Matter?
Understanding coral reproduction isn’t just for scientists — it is essential for conservation and restoration. As coral reefs face increasing threats from climate change, pollution, and ocean acidification, knowing when and how corals reproduce helps us time restoration efforts, collect larvae for reef seeding, and predict how populations may adapt in the future.
The WiseOceans Bora Bora Team
Did you enjoy ‘Mechanisms and Environmental Triggers of Coral Reproduction’?
Read More WiseOceans Discovery Blogs
Read More Marine Conservation Blogs
