The Ocean is a Strange Place After Dark

November 2021

Some phenomena in the ocean can only be witnessed after dark. Many fear what lies beneath. Now, we’ll dive into the inky depths and discover an extraordinary world. The blacker the night, the more wonders these waters reveal. Our dark seas are the stage for the most magical night on Earth.

Bioluminescence fluorescence ocean (Doug Perrine)

Bioluminescence makes the sea shimmer

The moon isn’t the only thing that illuminates our seas. Sometimes, the sea puts on a particularly special show. Luminous tides. Waves are breaking on the beach. The water is sparkling with electric blue lights. What we’re looking at is caused by billions of single-celled creatures, the Dinoflagellates. When disturbed, they emit blue light via a chemical reaction. This ephemeral phenomenon can be found throughout the ocean where there are dense gatherings of dinoflagellates, best-known places to witness are bays in Puerto Rico and Jamaica.

Animals glow in the dark

Bioluminescent firefly squid (Solvin Zankl)

During the moon’s darkest phase, the ocean puts on its most magical displays. Helped by the new moon’s tidal surge, thousands of female firefly squids migrate hundreds of meters up from the abyss. Using special cells called photophores, the squid makes their own light to communicate in the deep. Only females make this one-way trip, to bring their fertilized eggs up into the shallows to be dispersed by strong currents at the surface. The Japanese consider firefly squid a delicacy. By collecting them after they’ve released their eggs, they make little impact on their population.

Japanese fisherman collecting firefly squid (Toyama Bay)

Moonlight triggers the planet’s biggest orgy

There is nothing more romantic than a moonlit night, especially if you’re a coral on the Great Barrier Reef off Australia. One night a year in spring, the biggest orgy on earth is triggered by lunar light. Over 130 coral species simultaneously release their eggs and sperm into the water. This might be the most extraordinary example of synchronized behavior in the natural world. The corals also glow and it only becomes apparent after dark. By night, they can no longer use the sun to produce food but they can keep feeding. Corals possess stinging tentacles that catch minuscule creatures floating by.

Underwater photography of fluorescent coral (Cherie Bridges)

For more incredible ocean stories, watch the documentaries on BBC Earth YouTube Channel and on Night on Earth Netflix’s original limited series.