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Small, BB-like spheres floating up from a coral head during spawning. These bundles contain egg and sperm.
Gamete release by star coral (Orbicella (Montastraea)franksi) during mass coral spawning. Photo: Hickerson/FGBNMS

Every year, 7-10 days after the full moon in August, the reef-building corals of Flower Garden Banks National Marine Sanctuary put on a fantastic spawning display, one of the most abundant displays in the entire Caribbean. In ways that we still don't understand, each coral species times its gamete (egg and sperm) release for maximum benefit.

Close up view of Montastraea cavernosa polyps releasing egg bundles during spawning
Polyps of Montastraea cavernosa releasing egg bundles during spawning. This is a gonochoric species of coral.
(Image: FGBNMS/Schmahl)

Most scientists agree that these mass spawning events are designed to allow genetic mixing and dispersal of offspring over large distances. And, the sheer volume of the events allow for the fertilization and survival of a significant number of larvae despite the best efforts of predators.

Close up of Orbicella franksi coral polyps releasing gamete bundles during the annual mass spawning event.
Polyps of Orbicella franksi releasing egg/sperm bundles during spawning. This is a hermaphroditic species of coral.
(Image: FGBNMS/Schmahl)

Each year, sanctuary scientists and researchers from other facilities visit the sanctuary to observe this phenomenon in an effort to decipher even more pieces of the puzzle.

A transcript of this video is available in our Video Library.

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What We Know

  1. Not all species of coral are broadcast spawners (participate in mass spawning events).
  2. Most broadcast spawners are hermaphroditic, meaning that both sexes are represented in each coral polyp.
  3. Hermaphroditic species release bundles that contain both egg and sperm (gametes). These bundles rise to the surface and break open, allowing for mixing and fertilization.
  4. A few broadcast spawners are gonochoric, meaning that they have separate male and female colonies. (e.g. Montastraea cavernosa, photo above)

Stream of small, light pink particles floating on the surface of water at night.
Coral gametes floating on the surface of the ocean

  1. In gonochoric species, female colonies release bundles that contain only eggs while male colonies release a smoky, white cloud of sperm. Egg bundles float toward the surface then break open to mix with the sperm for fertilization.
  2. Floating gametes and gamete bundles create a sheen on the surface of the water.
  3. There is a distinctive odor above the water's surface during spawning.
  4. Mass spawning occurs in approximately the same sequence each year.
  5. Timing of the mass spawning at Flower Garden Banks is different from that on other reefs around the world.
    A cloud of small white spheres rising from a coral reef at night.  The spheres are gamete bundles released during the mass coral spawn.
    2007 mass coral spawning. Photo: FGBNMS Volunteer

At Flower Garden Banks National Marine Sanctuary we have observed the following species participate in the annual mass spawning event and we can predict quite accurately on which night(s) and at what time each species will spawn.

Orbicella (Montastraea) faveolata
Pseudodiploria strigosa
Montastraea cavernosa*
Orbicella (Montastraea) franksi
Stephanocoenia intersepta*
Colpophyllia natans

* gonochoric species.

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What We Don't Know

  1. The exact cue(s) for spawning to begin--although we do know that it is some combination of lunar cycle, solar cycle, water temperature, and chemical or light cues.
  2. How the corals coordinate their efforts so that multiple colonies of the same species are spawning at the same time
  3. Why some species are hermaphroditic and some are gonochoric

Through continued research and observation we hope to find the answers. For a listing of current research, please visit our Science Projects page.

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Coral Spawning in The Sanctuary

For more information about the annual mass spawning event at Flower Garden Banks National Marine Sanctuary, please visit our Coral Spawning at FGBNMS web page.

Spawning Expeditions

Coral Spawning 2014

Coral Spawning 2013

Coral Spawning 2011

Coral Spawning 2010

Coral Spawning 2009

Coral Spawning 2008

Coral Spawning 2007

Coral Spawning 2006

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