A scene from ‘Life of Pi’ depicting the bio-luminescent wonders of the sea.photo: AP
Have you ever wondered how fish and other marine life navigate deep in the ocean? At great depths, sunlight doesn’t penetrate as well. It is mostly dark except for a faint bluish glow – the part of sunlight that is able to penetrate that far. How then, do fish and other aquatic life see what’s in front of them? Like bats, there are some animals that seem to navigate using sound. But many others something even more fascinating: they manufacture their own light in a process called ‘bio luminescence’.
Many of you may have seen fireflies and glow-worms. Those little creatures that seemingly magically dance in the night are also bio luminescent. There are also fungi and mushrooms that can manufacture their own light. But deep inside seas and oceans, there are plenty more animals that do.
How do they do this?
Typically bio luminescence requires a chemical (often called a luciferin) and an enzyme called luciferase. With the help of the enzyme luciferin combines with oxygen and produces light. Such light is often also called “cold light” owing to the fact that these life forms are able to produce light with very little accompanying heat (unlike tungsten and CFL bulbs) earning the title “cold light”.
Making your own light is obviously very energy intensive. So animals use the process very economically, making light only when required and using it for some very specific purposes. The reasons vary from species to species. Some animals use it to navigate the waters. Others use it to attract prey and mates. The cookie cutter shark makes light in a positively sinister style. It has a small patch on its underside in the shape of a small fish. When that patch alone lights up through bioluminescence, it attracts a large predator to approach it thinking it is a tiny fish. The shark uses to opportunity to bite and nip into the clueless predator.
There are others, like plankton that uses it when they’re suddenly disturbed. The precise reason for why light is needed during a disturbance is not known although it some theories suggest that it is a way of denoting a danger-zone to others of their ilk. Then there are others that use it to show that they’re toxic and ward off predators. Few species use it ingeniously to camouflage with the colour of the blue light that penetrates through the water.
Deciphering the glow
Given that there are so many interesting uses for bioluminescence, many animals synthesise different compounds to produce light. Some do not synthesise light themselves but form symbiotic associations with other organisms such as bacteria to live inside them and synthesise the light. But despite so many animals being capable of bioluminescence, it has been a trying adventure for scientists attempting to study the phenomenon. For the large part, animals once held captured or killed are rendered incapable of producing such light. Light producing organs may critically fail. It becomes even more difficult for those trying to examine how the mechanism is regulated, turned on and off. And prevalent though it may be in the salty waters of seas and oceans, it hardly occurs in freshwaters. This too has puzzled scientists. Some suggest that freshwater life has been of existence for a very short time where species may not have had time to evolve the mechanism of making their own light. Others believe that freshwater tends to be muddy and murky where making one’s own light may not have much benefit.
While everyone scrambles to understand this intriguing phenomenon, it appears that for some time yet, species in the deep seas will be enjoying a whole new kind of special paradise.
This feature is from Agastya International Foundation (www.agastya.org), which runs hands-on science programmes for students
The cookie cutter shark makes light in a positively sinister style. It has a small patch on its underside in the shape of a small fish. When that patch alone lights up through bioluminescence, it attracts a large predator to approach it thinking it is a tiny fish. The shark uses to opportunity to bite and nip into the clueless predator.