The Open Sea: The World of Plankton

EDITORS:

JAMES FISHER, M.A.

JOHN GILMOUR, M.A.

JULIAN HUXLEY, M.A., D.SC, F.R.S.

L. DUDLEY STAMP, G.B.E., D.LITT., D.SC.

PHOTOGRAPHIC EDITOR:

ERIC HOSKING, F.R.P.S.

The aim of this series is to interest the general reader in the wild life of Britain by recapturing the inquiring spirit of the old naturalists. The Editors believe that the natural pride of the British public in the native fauna and flora, to which must be added concern for their conservation, is best fostered by maintaining a high standard of accuracy combined with clarity of exposition in presenting the results of modern scientific research. The plants and animals are described in relation to their homes and habitats and are portrayed in the full beauty of their natural colours.

Table of Contents

Cover

Title Page

Editors

Editors’ Preface

Author’s Preface

CHAPTER 1

INTRODUCTION

CHAPTER 2

THE MOVEMENT OF THE WATERS

CHAPTER 3

PLANTS OF THE PLANKTON

CHAPTER 4

SEASONS IN THE SEA

CHAPTER 5

INTRODUCING THE ZOOPLANKTON

CHAPTER 6

LITTLE JELLY-FISH AND LESSER FORMS OF LIFE

CHAPTER 7

SIPHONOPHORES AND THE LARGER JELLY-FISH

CHAPTER 8

MORE ANIMALS OF THE PLANKTON—BUT NOT THE CRUSTACEANS

CHAPTER 9

THE PLANKTONIC CRUSTACEA

CHAPTER 10

PELAGIC LARVAL FORMS

CHAPTER 11

THE PUZZLE OF VERTICAL MIGRATION

CHAPTER 12

LIFE IN THE DEPTHS

CHAPTER 13

PHOSPHORESCENCE AND PHOTOPHORES

CHAPTER 14

SQUIDS, CUTTLEFISH AND KIN

CHAPTER 15

PLANKTON AND THE FISHERIES

Glossary

Bibliography

Index

Colour Plates

Plates in Black and White

Copyright

About Publisher Page

EDITORS’ PREFACE

PROFESSOR HARDY began his marine biologist’s life over a third of a century ago on his return from service in the first world war. After Oxford and a scholarship to the Stazione Zoologica at Naples, he soon became a member of the Fisheries Department in the Ministry of Agriculture and Fisheries; and, in the middle ‘twenties, served as Chief Zoologist to the R.R.S. Discovery expedition, to the Antarctic seas, making a special study of plankton. His subsequent professorships—first at University College (now the University of) Kingston-upon-Hull; next at Aberdeen; and since 1945 at the University of Oxford—have brought him the highest academic status and honours, but have not kept him away from his beloved sea. In the closing stages of the writing of this volume, as the editors well remember, he was correcting the typescript, and completing his unique and wonderful colour illustrations, on the deck of the latest Royal Research Ship, Discovery II, scanning the contents of each netting or dredging, sketching new or rare creatures of the sea before their colour faded, applying himself to his research with an enthusiasm excelling that of most naturalists of half his age.

If the editorial board were asked to select from Professor Hardy’s many scientific qualities that which has contributed most to the creation of this extraordinary book, they would perhaps settle for enthusiasm. Throughout The Open Sea it is quite apparent that he is devotedly obsessed by, and interested in, animals; he is eternally curious about the nature of their adaptations and lives, brilliantly critical in the examination of their mysteries, acutely lucid and at the same time highly artistic in his depiction of them in his remarkable plates. It was a welcome burst of enthusiasm that caused Professor Hardy to write so much and so well of the life of the sea that he has written us two books instead of one. It is the first of these, concerned with the general natural history of the open sea and the world of its plankton, that we here welcome. The second part of The Open Sea concerns the open sea’s fish and fisheries, and will be published some time in 1957 or early 1958; like the present book, it will be illustrated by Professor Hardy’s own colour paintings, which represent what no colour-camera has yet been able to catch, and by black and white photographs by that most distinguished marine biologist and skilful photographer, Douglas P. Wilson.

To most readers the subject of this first of Professor Hardy’s two contributions to our series—the world of Plankton—will be relatively unknown and mysterious; but here the enlightened amateur naturalist is shown how, with modest equipment he may investigate it himself. The world of plankton is a world of complex anatomy, much of which can be understood only with the lens of the microscope. The life-histories of the animals are also complicated; some of them are extraordinary. To describe the plankton of our seas, and to set it in its pattern of community, climate, sea-scene and season is a major task. Professor Hardy has brought vast knowledge and experience and scholarship to a synthesis never before attempted.

THE EDITORS

AUTHOR’S PREFACE

ORIGINALLY it had been intended that the whole natural history of the sea, apart from that of the sea-shore and of the sea-birds already dealt with in the New Naturalist series, should be treated in one general volume. As the writing proceeded, however, it became clear that to do justice to the subject it would be impossible to include all its different elements within a single cover. There is the life of the plankton in almost endless variety; there are the many kinds of fish, both surface and bottom living; there are the hosts of different invertebrate creatures on the sea-floor; and there are those almost grotesque forms of pelagic life in the oceans depths. Then there are the squids and cuttlefish, and the porpoises, dolphins and great whales. In addition man’s fisheries now play such an important part in the ecology of our waters that they also must form a part of any general natural history of the sea.

Certainly there is too much material to go into one volume. There occurs, however, a fairly natural division between the teeming planktonic world and the other categories of life it supports: the fish, the whales and the animals of the sea-bed. This first book on the open sea deals mainly with the plankton; it aims at giving the general reader a non-technical account, save for the necessary scientific names, of its many remarkable animals and showing how, with only a little trouble, quite a lot of them may be seen and studied alive. Perhaps to some it may introduce a new world of life—a world so unusual that few of its inhabitants have homely English names at all. It is hoped, too, that it may be a guide to the plankton for university students who are beginning their studies in marine biology. The book also deals with the water-movements and the seasons in the sea; and it contains an account of the squids and cuttlefish, and of those queer creatures, including the deep-water (and often luminous) fish, swimming in the great depths only a little way beyond our western coasts. It will conclude by showing how a study of the plankton is helping us to have a better understanding of the lives of our commercially important fish. Later, and before very long, will come the sequel: a separate volume devoted mainly to fish and fisheries, but also including whales, turtles and other marine animals which are likewise, directly or ultimately, dependent on the plankton for food.

Before going any further I must thank the publishers and editors, not only for all the trouble they have taken over the production of this book, but also for the patience they have kindly shown over my delay in its completion. I accepted their invitation to write it in August 1943, some twelve years ago; it has, however, meant more than the writing. My excuse for its late arrival will be offered after I have made my main acknowledgment.

The value to the book of the remarkable collection of photographs by Dr. D. P. Wilson of the Plymouth Laboratory will be clear to all, but just how wonderful they are and consequently how lucky I am to have them as illustrations, may not at once be fully appreciated by those who are not yet familiar with the living plankton of the sea. Douglas Wilson has long been recognised as the leading photographer of marine life and his beautiful pictures in black-and-white and in colour which graced Professor C. M. Yonge’s The Sea Shore in this series of volumes will, I am sure, have been seen and admired by most of my readers. I, too, am showing some of his studies of the larger forms of life, such as those of cuttlefish or his unusual view of that strange jelly-fish, the Portuguese-man-of-war, taking a meal; it is, however, his photographs of the tiny plankton animals to which I particularly wish to draw attention here. Though they are taken through a microscope, they are photographs of creatures swimming naturally, very much alive and certainly kicking. Never before has such a series of photomicrographs of living members of the plankton been published; they are unique and will, I believe, be of immense value not only to marine naturalists but to all students of invertebrate zoology. They are the fortunate result of a remarkable combination; Dr. Wilson has brought his skill and artistry to work with that very modern invention the electronic flash. For the first time this device has made possible such instantaneous pictures at a very high magnification. It is not only that invention, however, which makes these pictures unique; while others will follow him, Dr. Wilson’s photographs will always have a quality of their own, because he is an artist as well as a scientist. He is not satisfied until he has produced a photograph that has an appeal on the score of composition as well as on that of scientific value. All his photographs except two (the stranded jelly-fish and squid) are of living animals. A few excellent black-and-white pictures by other photographers are included in some of the plates and these are acknowledged in the captions or the text.

It was my hope, and that of the editors, that in addition to his black-and-whites Dr. Wilson would have been able to contribute a series of colour photographs of the living plankton and especially of the richly pigmented animals from the ocean depths. At that time the electronic flash was only just being developed and he felt unable to attempt them. The movement of the ship at sea, he said, would prohibit the use of a long enough exposure to enable the deep-water animals to be photographed in colour by ordinary means; they quickly die and fade, and so must be taken as soon as they are brought to the surface. I had already had some experience in making water-colour drawings of living plankton animals on the old Discovery during the Antarctic expedition of 1925–27; the editors kindly allowed me to undertake a series of such studies to form the accompanying twenty-four colour plates. To obtain and make drawings of the full range of animals which I felt to be desirable, meant a considerable delay and this was added to an earlier postponement of my start on the book caused by my being appointed to the chair of Zoology at Oxford soon after I had accepted the invitation to write it. For several years the work of my new department and research to which I was already committed took all my attention.

All save seven of the 142 drawings in the plates were made from living examples or, in a few cases, from those taken freshly from the net when some deep-water fish and plankton animals were dead on reaching the surface. The seven exceptions, which are noted where they occur, were drawn from preserved specimens but with memories or colour-notes from having seen them alive; I should like to have drawn these too from life, but I could delay the book no longer. It may be of interest to record how the drawings were made. All the animals, except the larger squids and jelly-fish, were drawn either swimming in flat glass dishes placed on a background of millimetre squared paper where they were viewed with a simple dissecting lens, or on a slide under a compound microscope provided with a squared micrometer eyepiece; in either case the drawings were first made in outline on paper which had been ruled with faint pencil lines into squares which corresponded to those against which the specimen was viewed. In this way the shape and relative proportions of the parts could be drawn in pencil and checked and rechecked with the animal until it was quite certain that they were correct. The outline was then gone over with the finest brush to replace the pencil by a permanent and more expressive water-colour line; next all the pencil lines, including the background squares, were rubbed out and the full colouring of the drawing proceeded with. If rough weather at sea made such a course impossible, the living animal would be sketched in pencil, and painted, in perhaps one or two different positions, to give life-like attitudes and colouration without attempting to get the detailed proportions exactly right; it would then be preserved in formalin for accurate redrawing by the squared-background system when calmer conditions returned. The animals I have selected for illustration are mainly either those which are not included in the black-and-white photographs or those for which colour can add supplementary information. I have, for example, drawn some of the transparent but iridescent comb-jellies, but not the transparent and colourless arrow-worms or salps. I am most grateful to the Sun Engraving Company, who made the blocks for the colour plates, for the great care they have taken in making such excellent reproductions.

I must now make special acknowledgments in regard to these drawings. First I must record my thanks to Dr. N. A. Mackintosh, the Deputy Director in charge of the biological research of the National Institute of Oceanography, for kindly allowing me to accompany the R.R.S. Discovery II on two of her biological cruises in the Atlantic in the summers of 1952 and 1954. It is to the Discovery, with all her equipment of deep-water nets, powerful winches and laboratory accommodation, that 71 of these drawings are due, including all those representing the remarkable animals which live in the great depths over the edge of the continental shelf to the southwest of Britain. Without such facilities they could never have been made; actually three of them date back to earlier days when I had the honour of sailing south in the old Discovery in 1925. Next I must thank a number of kind helpers who have sent me living specimens of plankton in specially protected Thermos flasks from many parts of the coast: Mr. J. Bossanyi from Cullercoats, Dr. E. W. Knight-Jones from Bangor, Dr. Richard Pike from Millport, Professor J. E. G. Raymont from Southampton and Mr. R. S. Wimpenny from Lowestoft. Although I made many visits to different places to draw my specimens, there were still a number I could not get myself in the time available; these were supplied by these kind friends who were on the lookout for what I wanted at widely separated points. I am most grateful to Dr. Marie Lebour and to the Council of the Marine Biological Association of the United Kingdom for kind permission to reproduce some of her beautiful drawings of living plankton animals capturing their prey; these, which form my text-figures 26, 27, 35, 40 and 41, were originally published in her papers in the Association’s Journal in the years 1922 and ’23. Then I must thank Sir Gavin de Beer and members of his staff at the British Museum (Natural History), particularly Dr. W. J. Rees and Mr. N. B. Marshall, for kindly allowing me to make many of the black and white drawings in the text from specimens in the museum collections. I am similarly indebted to Dr. J. H. Fraser of the Marine (Fisheries) Laboratory at Aberdeen who has let me draw some of the beautiful plankton animals he has caught to the north and west of Scotland; and to Dr. Helene Bargmann and Mr. Peter David who have also kindly given me much help on looking out specimens from the Discovery collections for me.

With no less gratitude, I must make acknowledgments regarding the text. Apart from the more normal editorial comments and suggestions I particularly want to say how much I am indebted to my old friend—and once Oxford tutor—Dr. Julian Huxley, who read the whole book with the greatest care and made many valuable suggestions for its improvement. My typescript—how reminiscent of my undergraduate essays of 1919 and ’20!—was covered with his pencilled scribblings in the margin: “Surely you should refer to—, this might be made more emphatic” and the like; not all were adopted, but certainly a great many. The chapter on water movements was read by Dr. G. E. R. Deacon, and that on squids and cuttlefish by Dr. W.J. Rees; I am indeed grateful to them for a number of helpful suggestions they kindly made.

Finally I wish to draw the attention of those who are not scientists to a glossary at the end of the book giving a simple explanation of the few technical terms which have been unavoidably used; and for the zoologist I would point out that the authorities for the different specific names will be found quoted after these names in the index and not in the text where they are left out to avoid undue elaboration.

A.C.H.

CHAPTER 1 INTRODUCTION

THERE is a very simple fact about the sea which makes its inhabitants seem even more remote from us than can entirely be accounted for by their being largely out of sight. To make my point allow me to imagine a world just a little different from our own.

Suppose for a moment that we live in a country which is bounded on one side by a permanent bank of fog. It is a grey-green vapour, denser even than that often known as a London particular, and it has a boundary as definite as the surface of a cloud so that it is like a curtain hanging from the sky to meet the ground; we cannot enter it without special aids except for a momentary plunge and as quickly out again for breath. We can see into it for only a very little way, but what we do see is all the more tantalizing because we know it must be just a glimpse—a tiny fraction—of all that lies beyond. We find it has life in it as abundant as that of our own country-side, but so different that it might be life from another world. No insects dwell beyond the barrier, but other jointed-legged creatures take their place. Unfamiliar floating forms, like living parachutes with trailing tentacles, show their beauty and all too quickly fade from view; then sometimes at night the darkness may be spangled with moving points of light—living sparks that dart and dance before our eyes. Occasionally gigantic monsters, equal in size to several elephants rolled into one, blunder through the curtain and lie dying on our land.

To make a reality of this little flight of fancy all we have to do is to swing this barrier through a right-angle so that it becomes the surface of the sea. How much more curious about its unfamiliar creatures many of us might be if the sea were in fact separated from us by a vertical screen—over the garden wall as it were—instead of lying beneath us under a watery floor. Who as a child has not envied the Israelites as they passed through the Red Sea as if marching through a continuous aquarium: “and the waters were a wall unto them on their right hand, and on their left.”? What might they not have seen? Because normally our line of vision stretches out across the sea to the skyline and carries our thoughts to other lands beyond, many of us tend to overlook this perhaps more wonderful realm beneath us, or we seem to think it must be too difficult of access ever to become a field for our exploration or delight.

The aim of this book is to give the general reader an account of the natural history of the open sea around our islands and at the same time show how he may, with only modest equipment, see something of this strange world for himself. The amateur naturalist afloat—whether on a yachting cruise, on a fishing vessel, or just out in a rowing boat—may see much if he has the right kind of quite simple gear and knows how to use it; he may perhaps also be lucky and make original observations which will be a contribution towards finding an answer to one of the many unsolved riddles of the sea. The book will also give a sketch of some of the factors upon which the success of our great sea fisheries depend. The lives of the different fish are like threads woven in a web of life—a network of inter-relationships between many various creatures large and small, as complex as any on the land. The story of fishery research, which belongs mainly to our subsequent volume, is so closely linked with this unseen web, that it is hoped an account of these less familiar animals may be as interesting to the fishermen as to the naturalist; indeed many fishermen are naturalists and have much of importance to tell the scientist.

As our title indicates, the book will deal with the open sea—the sea beyond the coastal waters. The life of the intertidal zone has already been beautifully treated in this series of volumes by my friend Maurice (C. M.) Yonge (1949). The sea-shore can be studied by direct observation as the tide recedes and has long been a happy hunting-ground for the naturalist; he can lift up the fronds of seaweed, turn over stones, probe into rock-pools and dig into the sand and mud. Our methods of studying the life of the open sea must be very different; it is far from ‘open’ to the investigator, being in fact a hidden world, but this makes its exploration all the more exciting. Deep-sea photographic and television cameras are important new developments which promise much for the future; they, however, as also submarine observation chambers like the bathysphere, must for some time to come be regarded as very costly and specialist equipment giving us here and there direct confirmation of what we usually have to find out by other means. The diving helmet and the aqualung may help us to see something of this enchanting world in shallow water, but for the discovery of what is happening over wide stretches of the underwaters of the open sea we must devise more indirect methods.

The fact that we can see only a very little way below the surface indicates a property of water, and particularly of the sea, which is of fundamental importance to the life it contains. Held up in a glass, water appears so very transparent that we are at first surprised to find how quickly light is absorbed in the sea itself and what a little distance its rays will penetrate. Measurements made in the English Channel off Plymouth show that at a depth of five metres (just over 16 feet) the intensity of light is less than half that just below the surface, while at 25 metres it is only an insignificant fraction, varying between 1½ and 3 per cent. This at once tells us that the green plants, which must have sunlight in order to live, will only be found in the upper layers of the water.

The one real difference, of course, between animals and plants is a matter of their mode of feeding. We know that an animal of any kind, whether mammal, fish, shrimp, or worm, must have what we call organic food: proteins, carbohydrates (sugars, starches and the like) and fats, which have been built up in the bodies of other animals or plants. One animal may feed upon another kind of animal which in turn may have lived upon other kinds, and perhaps these upon yet others, but always these food-chains, long or short, must begin with animals feeding upon plants. Only the green plants, with that remarkable substance chlorophyll acting as an agent, can build themselves up from the simple inorganic substances by their power of using the energy of sunlight (photosynthesis); they split up the molecules of carbon dioxide, liberate the oxygen, and combine the carbon with the oxygen and hydrogen of water to form simple carbohydrates, which are then elaborated into more complex compounds by being combined with various minerals in solution. On the land we are all familiar with this elementary fact of natural history; my reason for recalling it is to emphasise that it is of universal application. The plants are the producers and the animals the consumers as much in the sea as on the land. Indeed ‘all flesh is grass’.