Animal Life in ttie Deep Sea.

Star (Christchurch), Issue 4996, 7 July 1894, Page 6

Animal Life in ttie Deep Sea.

♦ ■ ,•■: {Popular Science Monthly.) '■'■:..-: It is not surprising that the naturalist* : of the early part of the present century : could not believe in the existence of a fauna at the bottom of the deep seas. Tha absence of any evidence obtained by' accurate systematic research, together with the consideration of the physical charaoter of the ocean bed, were quite sufficient to lead scientific men of that period to doubt the existence of any • animal life in water deeper than a few hundred fathoms. We now know, how ever, that there is a very considerable' fauna at enormous depths in all the great oceans, and we have . acquired, moreover, considerable information concerning some of thoae peculiar physical conditiona of the abyss that fifty years ago were merely matters of speculation among scientific men. The peculiar physical conditions of the deep seas may be briefly stated to be these : It ia absolutely dark aa far aB actual sunlight ' is concerned, the temperature is only a few degrees above freezing point, the pressure is enormous, there is little or no movement of the water, the bottom is composed of a uniform fine soft mud, and there ia no plant life. All of these phy_ieal con* ditiona we can appreciate except the , enormous pressure. Absolute darkness wa ' know, the temperature of the deep seas is : not an extraordinary one, the absence ot ' movement in the water and the fine soft' mud are conditions that we can readily 1 appreciate; but the pressure ia far greater ' than anything we can realise. At a depth, of 2500 fathoms the pressure is, roughly speaking, 2. tons per square inch— that is 1 to say, several times greater than the pre.Bure exerted by the steam upon the ' piston of our most powerful engines. Or, to pub the matter in other words, tkfi pressure per Bquare inch upon the body of every animal that liveß at the bottom of • . the Atlantic Ocean ia abont twenty-five times greater than the pressure that will drive a railway train. It is only reasonable to suppose that the ability to sustain this enormous pressure can only be acquired by animali after generations of gradual migration- from shallow waterß. Those forms that ara brought up by the dredge from the depths , of the ocean are usually killed and die* ' torted by the enormous and rapid diminution of pressure in their journey to the surface, and it ia extremely probable that Bb allow water forms would be similarly killed and crushed out of shape were they suddenly plunged into very deep water.The fiah that live at these enormous depths are, in consequence of the enormous . pressure, liable to a curious form of accident. If , in chasing their prey or for 1 any other reason, they rise to a considerable distance above the floor of the ocean, 1 the gaßes of their swimming bladder become considerably expanded and their specific gravity very greatly reduoed. Tip to a certain limit the muscles of their bodies can counteract the tendency to float upward and enable the fish to regain its proper sphere of life at the bottom ; but beyond that limit the muscles are not Btrong enough to drive the body downward, and the fish, becoming more and more distended as it goes, ia gradually killed on its long and involuntary journey to tbe surface of the sea. The deep sea fish, then, are exposed to a danger that no other animals in this world are subject to — namely, that of tumbling upward. That euch accidents do occasionally occur ia evidenced by the fact that some fish, which. are now known to be true deep sea forms, were discovered dead and floating on the surface of the ocean long before our modern investigations were commenced. .Until quite recently, everyone agreed, that hb raya of sunlight could possibly '" penetrate the Bea to a greater depth "than a few hundred fathoms. Within the last few years a few authors haye maintained ■ that it is quite possible that a few rays o?~v sunlight do penetrate even to the greatest' depths of the ocean — a view mainly baaed - on the fact that so many deep sea animals possess extremely perfect and complicated eyes and very brilliant^ colours. There seems to me to be very alight grounds for this view. We have no sound information to go upon to be able to judge of the amount of light given off by phosphorescent animals ot the bottom of the "deep sea. The faint light they show on deck after their long journey from the depths in whioh they live to the surface may be extremely small compared with the light they give in their natural home under a pressure of 2\ tons to the square inch. The complex eyes that many deep sea animals exhibit wero almost certainly not evolved as such, but are simple modifications of eyes , possessed by a shallow water ancestry... The more recent experiments that have been made tend to show that no aunlight whatever penetrates to a greater depth, to take an extreme limit, than 500 ... fathoms. But although it ia very highly, probable that not a glimmer of aunlight ! ever penetrates to the depths of the ocean, there is in some places, undoubtedly, a very considerable illumination due to the phosphorescence of the inhabitants of the deep waters.