Coral spawn's a great show

August 18, 2013 

Brain coral releases eggs during a spawning event at a reef.

Each year around the August and September full moons, divers have a rare opportunity to witness a fascinating yet fragile annual reproductive phenomenon among coral reefs.

On Aug. 20, underwater enthusiasts eager to witness the phenomenon also can experience specially planned dive activities during the inaugural Upper Keys' Reef Crawl.

Continued survival of coral reefs is critically dependent on a reproductive strategy among boulder corals like brain and star corals, as well as elkhorn and staghorn -- two protected branching coral species. 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. Predators are unable to consume all of this food.

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. Eventually the planulae settle to the bottom to grow into polyps and form coral colonies.

Scientific observations indicate multiple environmental cues may be responsible for the coral spawn such as seasonal lunar cycles, water temperatures, and tidal and 24-hour light cycles. The polyp release date is not exact and can occur before or after a late summer full moon.

In 2013, the full moons fall Aug. 20 and on Sept. 19. Divers can check with dive operators throughout the Keys about joining coral spawning night dives scheduled around the full moon dates.

During the Upper Keys Reef Crawl, which runs through Sunday, three participating dive operators are offering specials on scheduled night dives around the coral spawn. Activities also include several daytime coral reef, artificial reef and wreck dives to explore the abundant sea life on dive sites between Key Largo and Islamorada.

For details and dive trip schedules, visit

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