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Florida Keys Reefs’ Annual Reproduction is a Fantastical Underwater Occurrence

Night divers soon can submerge on Florida Keys reefs for a chance to witness a fascinating yet fragile underwater reproductive phenomenon that occurs when coral polyps release millions of gametes (eggs and sperm) in synchronized mass-spawning rituals.

Typically sparked by full moons in August and September, the unique natural event illustrates the underwater environment’s sensitive circle of life.

The explosion and exchange of gametes into the water means the critical, continued survival of coral reefs, including boulder corals such as brain and star corals and branching species of elkhorn and staghorn corals.

Typically the eggs and sperm enter the water in massive quantities, a milky white excretion that, by nature’s design, spreads over a wide area to increase the probability of fertilization. At the same time, this overwhelms nearby predators with more food than they can consume.

When egg and sperm unite, the newly formed larva or “planula” rises to free-float in surface currents. Within just days or weeks, the planulae settle to the bottom to grow into polyps and eventually form coral colonies.

The coral spawn is scientifically observed and documented each year. What triggers the event remains unclear, though scientific observations indicate a strong connection to seasonal lunar cycles as well as multiple environmental cues such as water temperature and tidal and 24-hour light cycles.

After twilight, several critters and creatures come out of the coral reefs to feed and move about, offering extraordinary opportunities to see marine life that normally hides during sunlight hours. Colors are especially vibrant when they are illuminated with divers’ underwater lights.

Divers interested in a chance to view the underwater phenomenon of coral spawning can contact Florida Keys professional dive operators to join coral spawning night dives scheduled on or after the full moon dates of Aug. 26 and Sept. 24.