ANIMAL LIGHT AND THE MOON
By PROFESSOR C. M. YONGE
ANIMALS are possessed of many strange powers ; they can fly through the air, change their colour to harmonise with different backgrounds, and they can produce electric shocks. But none of these impress us more strongly than the ability, possessed by many of them, to emit light. This animal light, or bio-luminescence, is not a common sight in this country. Glow-worms may be seen in the summer-time like scattered points of light in the hedge sides in our southern counties. In some years immense swarms of microscopical animals, well named Noctiluca, may appear in the sea. These glow with phosphorescent light when they are disturbed and may illumine the waves as these break on the shore, or they may pick out in light the path of a ship as it cuts its way through the waters. But in the tropics fire-flies flit like dancing points of light over the surface of ponds and swamps, while the warmer seas contain innumer- able luminescent animals which drift past a vessel by night like balls and candles of light Animal light may be produced in the form of a luminous slime poured out by many marine animals when they are disturbed or sexually excited. In other animals the light is formed within special organs and can be turned off and on like a bull's eye lantern. The most complex of these light organs possess a reflector behind and a lens in front for focussing the light. They may even be screened to emit light of different colours. Deep-sea fish and squids possess the greatest variety of such organs. The darkness of the profound depths is broken only by flashes of such light or by the passage of a fish with light streaming from a series of organs along the sides of its body like that from the port-holes of a liner at night.
We associate light with heat, but this is only because we have as yet failed to produce light without wasting some of the energy expended in an accompanying formation of heat. Luminescent animals are more efficient. As long ago as 1667 Robert Boyle showed that bio-luminescence could only be produced in the presence of air. This is so because the process demands oxygen. A substance called luciferin is oxidised by the aid of a ferment, luciferase, and energy is liberated in the form of light. The reaction is essentially similar to all other oxidations, for instance, that which occurs when a candle is burnt, but the energy liberated takes the exclusive form of light.
This cold light which glows by night thus resembles nothing more closely than the light of the moon which fre- quently accompanies it. And, in a strangely indirect manner, the moon would appear in some cases to control its appear- ance. There is a widespread, although very imperfectly understood, association between the spawning of many diverse marine animals and the phases of the moon. In some of these animals the emission of light occurs only at the period of spawning, and so is associated, indirectly, with the moon.
In Bermuda and in the West Indies there occurs a small worm known to science as Odontosyllis. It lives in crevices in rocks where it normally lies hidden. But from time to time the animals come to the surface of the water to breed. This they do only in the third quarter of the moon, in some cases as often as six times in the year. They do not swarm in such vast numbers as their better known relative, the papolo worm of the South Seas, and some means of attract- ing the males to the females is therefore necessary.
The females appear suddenly about dusk or when it is fully dark and discharge simultaneously with the eggs a stream of brightly luminescent slime. This occurs several times and immediately attracts adjacent males, which rush in discharging short flashes of light and proceed to liberate their sexual products which fertilise the eggs. In many cases the biological significance of bio-luminescence is obscure, but there can be little doubt that in this case its production has the fundamentally important effect of attract- ing the males and so ensuring fertilisation of the eggs. Thus the moon, which in some mysterious manner appears to condition the period when these animals spawn, also con- trols their luminescent activities.
Dr. L. R. Crawshay, who observed the habits of these animals for many years when he was in charge of the Sponge Fishery Investigations at the Bahamas, has pointed out that their habits may well prove the explanation of a certain historical mystery. On the night before Christopher Columbus landed on one of the easterly islands of the Bahamas at the end of his first voyage across the Atlantic, at about to o'clock on the evening of October tith, 1492, he and his crew saw a strange light over the sea. This appeared from the poop of the ' Santa Maria ' like the flame of a small candle alternately raised and lowered.
Various explanations have been offered as to the origin of this light ; that it came from a native canoe, that it was a shore light or that it existed only in the excited imaginations of Columbus and his crew. But the vessel must have been over thirty miles from any land at the time when the light was seen which renders the first suggestion most improbable and the second impossible, while the record of the occurrence is too explicit for it to be lightly explained away by the third suggestion. But it is also recorded that the moon rose about one hour later which indicates that it was about one day before the last quarter.
It is at this period of the year, this phase of the moon and this time of day that Odontosyllis spawns with accom- panying luminescence in the surface waters. Dr. Crawshay has thus good reason for suggesting that this sudden waxing and waning light might very well have been due to this biological agency. The matter has further interest in connexion with the identity of the island on which Columbus first landed. This distinction is usually awarded to Wat- ling's Island, although some authorities claim that it was Cat Island. If Columbus had sailed to the north of Wat- ling's Island he would have passed near a shallow bank, from which Odontosyllis would rise to the surface for spawning, about four hours before, sailing at the speed he records, he could have encountered Cat Island. And this period did elapse between the appearance of the mysterious light and the first sight of land. Biological evidence thus favours Cat Island as the site of the landfall of Columbus. But whether we accept this as sound evidence or not it does remain a distinct probability that the first record of animal light associated with the phases of the moon was made by the eyes and recorded by the hand of no less a person than Columbus.
Previous page
