A few days ago, photographer Patrick Coyne filmed the exceptional images of dolphins lighting up California waters in the middle of the night. The video shows how, as the dolphins swim following the boat, flashes of light ignite around them, creating a magical and hypnotic image. These flashes are actually caused by small bioluminescent phytoplankton organisms found on the surface of the water.

What is bioluminescence?

Bioluminescence is the ability that some organisms have to create light naturally. This light is produced because of a chemical reaction which generates energy through light. Usually, the molecule involve is called luciferin, and when it reacts to oxygen, in a reaction catalysed by the enzyme luciferase, produces a cold light, generally blue, but sometimes it can be green, yellow or, rarely, red.

Many different types of marine organisms are luminescent, such as bacteria, dinoflagellates, jellyfish, worms, crustaceans, cephalopods, fish, and sharks, among many others. There are also organisms that cannot produce light on their own, but they incorporate other bioluminescent organisms into their bodies in order to have this ability. It is believed that in deep waters of seas and oceans where light doesn’t reach, more than 90% of species have the ability to emit light.

Bioluminescence can have several functions: offensive, to attract prey or to illuminate around and find it; partner recognition and / or attraction; communicative or defensive, to distract the predator, give away his position or even help the individual to camouflage himself with the light from the surface so they can’t be seen from below.

Bioluminescent phytoplankton

In these images, the organisms responsible for the bioluminescence are small unicellular organisms called dinoflagellates, that are part of the phytoplankton. The dolphins are swimming in an area with a high concentration of these organisms and when they are agitated by the movements of the dolphins, dinoflagellates react by emitting a flash of blue light of about 100ms duration, as a defense mechanism. In this case, dolphins are not their predators, but dinoflagellates are adapted to have this response to any physical disturbance. Thus, for example, when large concentrations of these organisms occur on sea surface, we can also observe the ocean lighting up with the movement of the waves, whether they are naturally originated or created by a ship in the open sea.

But, how does bioluminescence help dinoflagellates defend themselves against predators?

It is an alarm system. On the one hand, the flash of light surprises and scares the predator. On the other hand, the light reveals the position of the body responsible for the movement, therefore, its position is revealed and could become an easy prey since its predators know where it is. Another species that has this reaction in our waters is the luminescent jellyfish (Pelagia noctiluca) and in times of large concentrations of jellyfish on the surface, you can also see how their bodies light up with the movement of water caused by boats, waves or even dolphins.

Observing this phenomenon is a very special experience and difficult to capture with the camera, that’s why these images are exceptional. But bioluminescent waters not only occur in California, dinoflagellates can be found in tropical and temperate waters, even in the Mediterranean, creating magical nights on the coasts and in the open sea when right conditions for the proliferation of these organisms exist.