Moon's Over Miami: Coral Spawning Under the Stars


Last night’s full moon marked the starting cue for thousands of corals off of Miami Beach, to fall in love.


Within a week or two, trillions of eggs and sperm will swirl in the warm currents in a mass spawning ritual that hopefully results in a single coral polyp surviving thousands of years well into adulthood.

Beauty below the surface

Florida’s coral reefs extend 150 miles from the Dry Tortugas north to Martin County.  They began forming 5,000 to 7,000 years ago and have grown into the 3rd largest barrier reef system in the World.  Our coral reefs play host to hundreds of species of fish and invertebrates making for a beautiful underwater canvas of colorful life.


A single coral head is made up of individual but genetically identical polyps. Each polyp has a central mouth and tentacles.  It is from the central opening that either eggs or sperm are released.


Timing is Everything

This year, the delicate branching Staghorn coral (Acropora cervicornis) is expected to spawn on August 20th or 21st between 7:00 p.m. and 10:30 p.m. The timing is always spot on.  Not a second too early, not a second too late.

I have seen corals spawning underwater as part of my marine biology graduate studies and it really is this magical event that out of the underwater darkness, you suddenly see a couple of bright pink eggs burst from a few polyps then…

Boom! You’re in the middle of an underwater snow globe!


Understanding The Basics

A threatened species, scientists have paid close attention to the reproductive behavior of the Staghorn coral.  Understanding coral reproduction aids recovery of threatened populations and strengthens efforts to limit coastal pollution and sedimentation that can interfere with successful coral spawning.


It Starts as a Moonlit Romance

So, how is it that thousands of individual corals know when it’s go time?  It was thought that the moon’s phase was the trigger as it controls the tides.  It would be beneficial for corals to reproduce during a time when their buoyant embryos could ride stronger currents as far as possible to populate other reefs.

New studies have shown, though, that the moon most likely acts as a visual cue for the timed affair.  Primitive photoreceptors like the ones found in sunflowers have now been found in corals and respond quite directly to moonlight.


Then it Gets Hot Under There…

A more long-term cue for corals to let it all go is water temperature.  There is a seasonal difference in the timing of coral spawning in the southern hemisphere versus the northern hemisphere.  In the southern hemisphere, where water temperatures are warmer earlier in the year, corals spawn from January to March, in middle latitudes, March to May, and in Miami, between June and October.


Changing Times

In today’s quickly changing climate and coastline, the resiliency of corals to keep up is being tested.  Already, several scientific studies are reporting that sediment particles from dredging can stick to eggs and sperm weighing them down and preventing them from reaching the sea surface.  This will ultimately reduce their chances for successful fertilization. We may end up seeing residual negative effects to the coral population as a result of the dredging disaster that is the expansion of the Port of Miami.

As global temperatures rise, the timing of these massive spawning events may change causing a ripple-effect to other species like, whale sharks, who feed on coral embryos. We may even see coral populations shift further north as water temperatures in higher latitudes grow warmer.


See Them for Yourself

We are lucky to have 3 coral reef tracts within easy access from shore to provide us with plenty of opportunities to catch the magic as it happens.


Check into these local dive charters offering evening Coral Spawning Dives:

Read the full article at Midtown Miami Magazine