Marine Science

Coral Gametes 101: Introducing the Birds and the Bees Under the Sea

Acropora  coral gametes gathering at the surface during a spawning event in Belize, 2019.

Acropora coral gametes gathering at the surface during a spawning event in Belize, 2019.

What are gametes anyways?

Well, in biology lingo, gametes are male and female reproductive cells… eggs and sperm.

Corals have sperm and eggs?

Yes, that’s right. Acropora species, like many (but not all) corals, are hermaphrodites. This means they contain both male and female reproductive gametes. Although Acropora can asexually reproduce, sexual reproduction is essential to maintain their genetic diversity.

How does spawning work?

It takes two to tango. One egg and one sperm join to create an embryo, which develops into a coral larvae. Coral species either rely on internal fertilization or external fertilization for sexual reproduction. Acropora species fall under into a category of coral called broadcast spawners, who release gametes into the water column for external fertilization to occur. Brooders, on the other hand, fertilize inside their bodies and release fully formed larvae.

Acropora package their gametes into tiny pink bundles, which they synchronically release during a spawning event. For Acropora cervicornis (Staghorn coral) and Acropora palmata (Elkhorn coral), this event takes place a few nights after the full moon in August. Some species spawn more often, but Acropora species prefer that late summer mood lighting…

Gamete bundles are fully of fatty lipids, causing them to float up to the ocean’s surface. Water movement and wave action agitate the gamete bundles, eventually causing them to break apart into eggs and sperm. At the surface, eggs and sperm mix with gametes released from other colonies … and the rest is history…

Gamete Blizzard 2019

Imagine a blizzard where the snowflakes are pink and instead of falling down, they float up. And instead of snowflakes, it’s precipitating the last few crab legs at an all you can eat buffet...

You following? Great. This is essentially what coral spawning is like.

All the creepy crawlies come out during spawning events. And when corals release their gamete glitter into the water, everyone on the reef wants a bite. Researchers are sure to dawn hoods, gloves, and full body wet suits to protect against the onslaught of brain-sucking worms that emerge during spawning events (Okay, maybe not brain-sucking, but who wants to test that…). The fatty gamete bundles provide a nutritious snack for many reef organisms, making these night dives particularly lively.

Take a look at this video for a glimpse at the pink blizzard that takes place beneath the waves.

Elkhorn (Acropora palmata) and Staghorn (Acropora cervicornis) corals reproduce by releasing egg-sperm bundles into the water. This event takes place at night, a few days after the full moon in August.