"THE BURNING OF THE SEA"

New Zealand Herald, Volume LXXVII, Issue 23719, 27 July 1940, Page 7 (Supplement)

"THE BURNING OF THE SEA"

Nature Notes

By A. G. STEVENSON.

Yachtsmen sailing in the Gulf often notice that the sea at night is highly luminous. A stroke of an oar or any other disturbance of the water causes it to break into a myriad points' of light, while the dinghy trailing astern seems to be sailing on a sea of fire. This luminescence, or phosphorescence, as it is commonly called, is caused by millions of jelly-like creatures called salps, which drift into the Gulf from time to time. Normally they are invisible bits of jelly in the ■water, but any disturbance causes them to become brightly luminous for a moment or two. Minute Marine Creatures The power of producing light is not uncommon in the animal world and is far more widespread in the sea than on land. It is quite common among. the many minute marine creatures, as well as crustaceans, molluscs, worms and even fish. On land it is restricted mainly to insects, although it appears also in some kinds of centipedes and worms. As for plants, it is confined to bacteria and funtri. When largo numbers of luminous creatures congregate in one spot the whole sea appears to be lit up and such phenomena have aroused interest from the earliest times. Aristotle mentioned it in his writings, and no doubt long before that fishermen have marvelled at the "burning of the sea" 85 it was sometimes called. Many theories have been advanced to account for this strange light. great-explorer, Franklin, considered it to be due to friction between the various salts in the water setting myriads of tiny electric sparks. But in 1667 'the great chemist, Robert Boyle, was able to show that the production of light could take place only in the presence of air, an . observation that practically proves ■ organic luminescence to be a chemical P r °ces S in the nature of oxidation. < further researches have confirmed 1 *ae theory that the production of light i

is the result of the interaction between ferment substances secreted by the animal. A substance called luciferin unites with oxygen from the air to produce light and a second ferment, called luciferase. acts as a kind of chemical lubricant which assists this uniion in some mysterious way. Both luciferin and luciferase can be isolated from the animals which produce them, so that it is possible to produce animal light in the laboratory and experiment with it in various ways. A peculiarity of this light is that it is a "cold" light. It is unaccompanied by heat of any kind and is thus far more efficient than any artificial light produced by man. In producing artificial light we expend heat and our methods are highly inefficient because only a very small percentage of the energy used manifests itself as visible radiation. All the rest is wasted heat. Almost all drifting marine creatures are capable of producing light and occasionally they will swarm together in such countless numbers _ that the whole sea seeitns to glow with a pale coldl light. Darwin gives a picturesque account of such an occurrence which he witnessed when sailing on a very dark night just south of the River Plate. He said that there was a fresh breeze and tliat the crest of every wave raised by it gleamed with pale light. The- vessel's bows raised two billows of liquid phosphorus while her wake was like a milky train. As far as the eye .could see the ocean was lit up by the glowing crests of waves. Like an Electric Torch

Such displays are usually caused by immense numbers of single-celled organisms, called Protozoa. Two especially, Noctiluca and Pyrocystis, have exceptional powers of producing light. Many jellyfish, too, have the power of general luminescence, appearing like globules of fire waxing and waning in brightness. Some marine worms secrete a luminous substance over almost the entire surface of their bodies, and produce a brilliant violet or blue-green

light. fThe crustaceans, creatures of the shrimp or prawn type, are often equipped with definite light organs of great complexity, and are able to turn the light on or off just like an electric torch.

Among the molluscs there is a delicate white bivalve commonly called the Piddock.'lt lives in the soft rock and spends the whole of its life within

the walls of its self-made prison. Strangely enough, this shellfish is one of the most luminous of all marine animals- It produces a very powerful greenish-blue light and one wonders what purpose this could serve within the close confines of a hole in the rock. The octopus and its near allies are never luminous but in the squids lightproducing organs are common and often very elaborate. On land the lowest forms of life producing light aro certain kinds of bacteria. These are responsible for the light which appears on dead fish and they occasionally gather in groups on living animals, giving them a luminous appearance. In fact, one school of investigators considers that those bacteria live within the luminous organs of many animals and are really the cause of the light produced there. In the insect world we have the well-known firefly and glow-worm. The firefly is common in some parts of America and a display of their dancing lights on a dark night is said to be truly entrancing. I have seen fireflies

in JFiji, but only at rest. What struck me particularly about them was that a gentle blowing caused them to glow more brilliantly, just as a hot ember would do. Our own familiar glow-worm is really the larva of a fungus-gnat, Arachocampa luminosa, related -to the crane-flies and mosquitoes. Its light is produced by special organs situated in the tail segments of the larva's body, and acts as a lure for midges on which it preys. Attracted by the light the midges become entrapped in a system of hanging, .sticky threads. While it appears fairly obvious in the case of insects the reason for the production of light in marine animals is in most cases a complete mystery, and wo can only hazard a guess as to what part it plays in the life of the animal. Perhaps it is to attract prey or perhaps it aids members of a species to recognise each other. But wo can be certain of nothing at present and the function of this light is likely to remain a puzzle for scientists for some timo to come.