Every year on beaches all around the globe something amazing happens. Late at night, long after the sun has disappeared and the darkness has settled, the surf of the waves along the shore begin to glow. This however is not some crazy way of light reflecting off the water or some poisonous runoff from a nearby construction site, but the result of natural phenomenon called bioluminescence.
A special type of phytoplankton - a single celled alga called dinoflagellates, has evolved a chemical reaction, which causes them to emit light whenever agitated. They live only in seawater and are mostly very tiny, although some of them can grow large enough to be seen with a naked eye. During the day they tend to rise to the oxygen rich surface, where they collect sunlight and begin to bloom. This gives the ocean a rusty, reddish hue, which is why the phenomenon is often referred to as a Red tide.
Movement in the water, like that of swimming fish or crashing waves, sends small electrical signals along their cell membrane, triggering the reaction. The membrane has special, voltage sensitive channels which convey the electrical pulse to small compartments inside, filled with luciferase – a protein which emits a neon blue light. At night, whenever they are in high enough concentrations, this causes whole beaches to light up. Scientists believe this is a defense mechanism, meant to startle predators into thinking they aren’t safe to eat, as well as attracting other, even larger predators, who can get rid of the danger for them.
There is another, even less understood, but very closely related phenomenon, called the Milky seas effect. Instead of along the shore, here large areas of seawater, hundreds or sometimes even thousands of square kilometers start to illuminate. Sometimes they are so bright, that they can be seen from satellites, orbiting the Earth. It is an event, described by sailors for centuries and which keeps baffling scientists to this day. As opposed to the Red tides, where the lighting effects last for only a couple of seconds, these tend to go on for hours or days even. So far there isn’t any evidence to support the idea, that dinoflagellates or any other known bioluminescent creatures are capable of such an achievement.