One of the biggest thrills of a yacht voyage for guests and crews alike is to dive into a nighttime sea that explodes with a stunning underwater firework display. Just as this greenish light outlines otherwise invisible dolphins playing in your bow wave, you own body glows with thousands of tiny lights. Float on your back, wave your arms and legs and make glow-angels for the folks on deck... ahhhh!
But what exactly is this shimmering display?
If you said phosphorescence, sorry, no. Phosphorescence is caused when inanimate objects absorb energy, then slowly glow. The light you see in the sea is alive – hence its name bioluminescence – literally, “living light.”
Apart from the light emitted by a few land animals like fireflies, the vast majority of bioluminescence is only seen in the oceans, whether warm or cold. But why do sea creatures put on such a show?
Scientists believe that the ability to glow in the dark has evolved over 30 separate times in nature – and there are many different theories as to why:
Glowing lights don’t seem like great camouflage, but sometimes truth is stranger than fiction.
The underbelly of the cookie-cutter shark glows, camouflaging it against the brighter surface of the water when seen from below – except, that is, for a small patch which doesn’t glow. This dark part just happens to be bait fish-shaped. It attracts predators, and the cheeky shark grabs a bite when they are tempted close. It even has special cookie-cutter teeth so it can take a chunk and swim away before the other fish knows what’s hit them!
Perhaps the most famous example of this are Anglerfish that lure their prey within reach with a “lamp” on a dangling “rod” hung in front of their jaws.
But the bioluminescence you’re most likely to see is caused by much smaller lifeforms. Dinoflagellates are mostly single-celled plankton that use a whip or “flagellum” to propel themselves along. Many can photosynthesize, employing a light-giving chemical that’s similar to the chlorophyll they use to get energy from sunlight. This makes their bioluminescence even brighter after a very sunny day. When they detect a predator, they luminesce to attract even larger predators to attack their attackers! And as they can’t differentiate between a fish, a yacht or a human, they’ll flash their alarm whenever the water is violently disturbed. Hence the starburst you get when swimming, as well as the glowing trail in your yacht’s wake....
Other creatures flash for love rather than out of fear . Ostracods (tiny crustaceans sometimes known as seed shrimp) attract their mates under the sea like fireflies.
Just as squids use ink to confuse predators in the daytime, some can squirt out a cloud of glowing liquid at night. Other sea creatures emit a really bright flash to try to temporarily blind and confuse predators.
Bacteria seem to use light to communicate – it helps them group together and join host organisms and It’s known that squid use color to communicate during the daytime.
Perhaps the most obvious reason sea creatures produce light is to see, and of course, some of them simply use their light as a spotlight to find prey. But once again, nature can be even more cunning than that. The evil-looking deep-sea monsters called Black dragonfish produce a red glow so they can detect red prey (normally invisible in the deep ocean where the red light is filtered out). The prey can’t see the dragonfish – next thing it knows it's been grabbed by a row of jagged teeth.
Now you’re an expert on bioluminescence, how do you find it when you want to see it? The best times are around the new moon, when the sky is darkest – and it’s even better if the days are really sunny in order to prime those dinoflagellates. So bust out those snorkels and dive into the living light – just beware if you’re skinny dipping as it makes everything it outlines glow!
Have you seen bioluminescence from the yacht? Where's the best region to look for it?