One of the most spectacular sights on a night dive in the ocean is to witness the hundreds of tiny star-like bioluminescent phytoplankton scintillating like a starry sky as you move through the dark water. Towards the end of a dive, just shield your underwater flashlight and wave your hands through the water in front of you, and be mesmerized by the tiny glowing specs of plankton. So what kind of plankton are these? And how do they emit that bluish glow that you see in the below picture of the plankton washed on shore?
Certain creatures both on land and sea can produce light through chemical reactions taking place within their bodies known as Bioluminescence. The bioluminescence results from a light-producing chemical reaction also called chemiluminescence. Certain types of chemicals when mixed together produce energy which ‘excites’ other particles on vibration and generate light which causes the glow. The group of chemicals involved to make plankton glow are broadly termed luciferins and the light is produced by a series of oxidation reactions set off by a catalyst called luciferase. The bioluminescence in plankton is very high in several forms of Plankton and is a form of cold light or luminescence.
Plankton consists of any drifting organism (plant or animal) that inhabit the oceans and provide a vital source of food to larger aquatic organisms such as fish. A vast range of plankton, both zoo plankton and single-celled animal plankton are known to be bioluminescent. Bioluminescent phytoplankton occur in all the world’s oceans.The most common of these are Dinoflagellates which are tiny unicellular marine plankton also known as fire plants.
Dinoflagellates are the most common source of bioluminescence in our oceans and the chances are the sparks flying off your oar, the bow or wake of your boat are billions of tiny dinoflagellates or copeopods. These creatures get their name by their ability to swim by two flagella, which are movable protein strands attached to their bodies.
Bioluminescence is used to evade predators and acts as a defense mechanism in dinoflagellates. Dinoflagelletes produce light when disturbed and will give a light flash lasting a fraction of a second. The flash is meant to attract a predator to the creature disturbing or trying to consume the dinoflagellate. The light flash also surprises the predator causing it to worry about other predators attacking it, making the predator less likely to prey on the dinoflagellate.
However the experience of swimming in the midst of these amazing creatures is something that must be witnessed at least once by every scuba diver or avid snorkeler. Several Dive Operators offer special bioluminescent phytoplankton dives or snorkeling expeditions, in seasons when plankton is at its peak brought by ocean currents. These swims would usually be in absolute darkness to witness the both the starry skies above and the starry seas below.