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Divers in the Florida Keys have become subsea voyeurs of sort, witnessing a fascinating yet fragile annual reproductive phenomenon on coral reefs.

Coral spawning occurs in August and September a few days after the full moon.

Continued survival of coral reefs is dependent upon the reproductive strategy among boulder corals like brain and star corals, as well as elkhorn and staghorn branching corals.

Millions of gametes, or reproductive cells, are released underwater in a synchronized mass-spawning exchange, enabling the eggs and sperm to enter the water over a broad geographic area to maximize the chances of fertilization.

When egg and sperm unite, newly formed larvae, or planulae, ascend to the surface to free-float in the current for days or sometimes weeks. Some planulae settle to the bottom to grow into polyps and potentially form coral colonies.

In the Keys, a number of dive shops stage special trips to view the spectacle that many describe as an “upside-down underwater snowstorm.”

Fla keys

Annette Robertson photographs corals discharging gametes in the Florida Keys National Marine Sanctuary late Tuesday, Aug. 27, 2013, off Key Largo, Fla. During the first few days after full moons in August and September corals in the Florida Keys go through an annual ritual where reproductive cells are released in a synchronized mass-spawning exchange, enabling eggs and sperm to enter the water over a broad geographic area. When egg and sperm unite, newly formed larvae can settle to the bottom to grow into polyps and potentially form new coral colonies.

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