Going for a night paddle in a protected cove on the British Columbia coast, I first tested the water by throwing a rock into the sea. A green flash radiated from where it ker-plunked into the water. The bioluminescence was in. A few minutes later we were paddling along, glowing green whirlpools trailing our paddle blades. Below us, streaks wiggled through the depths: the disturbances of small fish in the bioluminescent water. A few minutes later, we saw a glowing cacophony of green splashes: four sea lions were feeding on fish, and the thrashing created a churning, glowing sea.
The glowing-sea phenomenon is known as bioluminescence. It’s caused by a tiny critter called Noctiluca scintillans, commonly known as sea sparkle.
What is it?
Noctiluca is a tiny dinoflagellate, a form of plankton too small to see with the naked eye. It exists in the sea nearly worldwide. Like many types of plankton, Noctiluca photosynthesize energy from the sun via by a symbiotic relationship, in this case most commonly with green algae, which is why the light they emit often has a greenish hue.
The bioluminescence is trigged by a mechanical disturbance: wave action, a paddle blade, or a fish swimming through a patch of Noctiluca-dense water. This starts a chemical reaction that releases light through enzymes inside its cells. The more distinct the disturbance, the more sharper the flash.
The adaptive advantage of this light release is the greater mystery. One theory is that the flash startles away predators. Another is that the light actually attracts even bigger predators, which would scare off whatever was a potential threat to the plankton. If this is true, it’s the plankton equivalent of calling the bouncer when there’s a troublesome guy at the bar.
Where to See It
It’s hard to predict the best times and places see bioluminescence, because noctiluca occurs nearly worldwide, and its concentration varies with weather, seasons, and ocean patterns. Some spots, like Bioluminescent Bay in Puerto Rico or the German Bight, are famous for concentrations of sea sparkle. But it’s also a not-uncommon, if less predictable occurrence in many places around the world. Bays with a narrow outlet tend to collect higher concentrations of plankton than those that are flushed by currents, and tend to have more bioluminescence.
When To See It
More important then where is often when. Bioluminescence is mostly a summer phenomenon, when algae blooms often occur. There’s always an element of luck, but look for a new moon and a place with little light pollution: the dark skies will make the glow stand out.
Not So Great For You
Dense concentrations of Noctiluca aren’t great to ingest, as they can be high in ammonia. It’s great to throw rocks at and paddle through, but not the best for swimming.
It’s Not Just Plankton
Tiny dinoflagellates aren’t the only critters to use bioluminescence. Deep sea Vampire squid have bioluminescent cells on their skin that allow them to turn themselves “on and off”. The anglerfish, also a resident of the extreme depths, uses a bioluminescent “lure” on a slender tendril to “go fishing”. The glowing lure attracts other fish, which the anglerfish promptly gobbles up.