Conditions of life in the sea : a short account of quantitative marine biological research

Front matter

22102076882

Med

CAMBRIDGE BIOLOGICAL SERIES

Preface

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Modern oceanographical research has been developed from the work of Mun-ay, Buchanan and Dittmar, which was based on the collections and observations made during the Challenger expedition. Cleve and Pettersson then attempted to trace the origin of the water which, from season to season, drifted to the shores of Scandinavia. Knowing that different sea-areas were characterised by different facies of microscopic life they endeavoured to press the study of the plankton into the service of hydrography, and hydrography into that of meteorology. Like Hensen’s, their object was a restricted one, but the idea involved w^as so fruitful that a host of investigations sprang from it. To it we owe new determinations of the chemical composition, and the physical properties of sea water ; and the invention of beautiful apparatus for the tracing and measurement of ocean currents ; as well as the mathematical investigations by Sandstrom, Helland-Hansen, and D’Arcy Thompson of the movements of water-masses in the sea. Then if different plankton types are to be associated witji water of different chemical and physical properties the causes are to be sought. Again new investigations were instituted, and the study of the association of changes in the salinity and temperature of the sea, with concomitant changes in the nature and abundance of the plankton, was extended to the study of the migrations and breeding habits of fishes. Queer side-issues have arisen in the course of these investigations : the study of the physical condition of the particles composing the sea-bottom, for instance, and the association of changes in the viscosity of the sea water with the movements of the plankton.

Possibly more was anticipated from the direct results of the quantitative investigation of the plankton than has actually been acquired. Probably too, Hensen, Cleve and Pettersson under-rated the difficulties of the work, and under-estimated or overlooked sources of error. It would be strange indeed if they did not I Criticism, both of methods and results, has not been wanting. How much, for instance, has the quantitative study of marine life

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PREFACE been prejudiced in this country by the publication of Haeckel’s Plankton-Studien ! And how many people who have read that brilliant but injudicial essay have seen Hensen’s reply to it ! I have tried critically to consider the weight of the various objections that have been made against conclusions deduced from the quantitative study of marine life, and trust that I have not under-estimated these. Adverse criticism, which would surely have been fatal to the development of an unsound method of investigation, has certainly stimulated research on the lines suggested by Hensen. Lohmann’s work, for instance, was essentially critical and yet, more than any other piece of plankton investigation published since the appearance of Hensen’s first memoir, it will facilitate the quantitative study of the plankton. Admittedly imperfect and incomplete as are these investigations, their results form nevertheless the most fascinating chapter of modern marine biological research, and as such may be commended to the reader.

I am indebted to my colleagues Miss M. Allen, and Mr H, J. Buchanan- Wollaston for much kind assistance ; to Dr F. W. Gamble for reading part of the manuscript ; and to Mr A. E. Shipley for many suggestions, and much advice.

J. J.

Liverpool, July 1908.

Chapter I. The Exploration Of The Sea

Methods of oceanographical investigation — The Challenger — Later Expeditions— Oceanographical apparatus — Sounding machines — Water-sample bottles and thermometers — Salinity and density of sea water — The International Fishery Investigations — Biological investigations — Dredging and trawling — Beam trawl and otter trawl — Deej) sea dredging and trawling — Other fishing apparatus — Pelagic fishing apparatus — Tow-nets and similar apparatus Page 1

Chapter II. The Oceanography Of The North-western Ocean

The British Islands and the continental shelf — The Greenland-Shetland elevation — Norwegian and Atlantic basins — The fore-shore — Sea-bottom deposits — Terrigenous deposits — Pteropod Ooze — Globigerina Ooze — Radiolarian Ooze — Diatom Ooze — Red clay — Temperature of the sea — Colour and transparency of the sea — The water circulation in the North Atlantic and Polar seas — The Gulf Stream and its offshoots — The European Stream — The Wyville-Thompson barrier — The Norwegian branch of the European Stream — Perturbations and periodic variations of the European Stream — Climate and hydrography 30

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CONTENTS

Chapter III. Life In The Sea

Zones of life — Littoral, laminarian and coralline zones — Benthos, nekton and plankton — The deep-sea fauna — The migratory fauna — The plankton — Constituents of the plankton. Fishes, Ascidians, Crustacea, Mollusca, Worms, Echinoderms, Coelenterates, Ctenophores, Protista, Peridinians, Foraminifera, Radiolaria, Diatoms, other Protista . 54

Chapter IV. Life In The Sea

Permanent and transitory plankton — Life-histories of marine animals — Direct and indirect modes of development — Larvae of marine animals — The struggle for existence in the sea — Destruction in the sea — Fecundity of marine animals — Protection of the eggs and larvae — Seasonal variations in the plankton— Migrations of fishes — The struggle for food in the sea ... 81

Chapter V. The Sea-fisheries

Economic marine products — Exploitation of the sea — Influence of man on the marine fauna — Methods of fishing — Trawlers, drifters and liners — Pelagic and demersal fishes — Classes of fishermen and their economic condition — The shell-fisheries .......... 102

PAET II.

QUANTITATIVE MARINE BIOLOGY.

Chapter VI. Quantitative Plankton Investigation

The Hensen nets and methods — Construction and method of use of quantitative plankton nets — The catch and its preservation — The “Korbnetz” — The Petersen-Hensen net — Estimation of the catch of a quantitative plankton net — Volume, chemical composition, mass and enumeration of

CONTENTS

XI the catch — The Stempel-pipette — Validity of the Hensen methods — The objections of Haeckel and Kofoid — Lohmann’s investigations — Other quantitative plankton methods — Capture of plankton by appendicularians — Defects of the Hensen methods 117

Chapter VII. The Distribution Of The Plankton

The mixing of the plankton in the sea — Experimental errors in the Hensen methods— Vertical distribution of the plankton — Stratification of the plankton — Heliotropic migrations — Changes in the distribution of the plankton due to temperature, viscosity and convection currents — Inshore and offshore plankton — Plankton types — Oceanic and neritic plankton — Distribution of the plankton according to hydrographic conditions — Atlantic and North Sea plankton — Cleve’s investigations — Plankton mixtures — Halistatic planktons . 142

Chapter VIII A Census Of The Sea

Difficulties and uncertainties of the estimation of the life of the sea — Density of the plankton of the North Sea — Average plankton contents of the North Sea — Abundance of diatoms, peridinians and copepods in the sea — Variations in the density of the plankton with the locality — Density of the micro-plankton — Density of fish-eggs and larvae in the sea — Hensen’s “Nordsee Expedition” of 1895 — Absolute abundance of certain species of fish in the North Sea — Errors in the estimations — Density of life on the sea bottom 157

Chapter IX. The Productivity Of The Sea

Productivity of the North Sea — Produce of the North-Western fishing area — Productivity of an inshore fishing area — Productivity of the shell-fisheries of the West coast of England — Cultivated water areas — German carp fisheries - -A cultivated mussel fishery — The absolute productivity of a sea area — Composition of marine produce — Relativ'e productivity of the sea and the land — The impoverishment of the sea — Productivity of the sea in different latitudes 178

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CONTENTS

Chapter X. The Conditions Of Life In The Sea

The nutrition of marine organisms — Plankton as food-stuff— Ultimate food-stuffs in the sea — Modes of nutrition among marine organisms — Holophytic organisms — Saprophytic organisms — Myxotrophic animals — Saprozoic animals — Law of the minimum — Physical conditions and the metabolism of marine organisms — Temperature — Salinity — Migrations of fishes and salinity changes — Sunlight — Photo-synthesis — Colour of sea water . . . 206

Chapter XI. Bacteria In The Sea

Types of bacteria — Biological reactions — Distribution of bacteria in the sea — Halibacteria — Luminous bacteria — Putrefactive bacteria — Prototrophic, metatrophic and paratrophic bacteria — Fermentation bacteria — Sulphur bacteria — Nitrifying bacteria — Nitrogen-fixing bacteria — Denitrifying bacteria — Temperature and denitrification 253

Chapter XII. The Circulation Of Nitrogen

Atmospheric, organic, and inorganic nitrogen — Animal and plant metabolism— Elimination of waste products — Putrefactive decomposition— Breaking down of dead organic matter — Nitrification — Sewage and its purification — Denitrification — Drainage of nitrogen from land to sea — Mass of nitrogen annually added to the sea — Utilisation of land drainage by marine organisms — Transmutation of nitrogen through series of marine organisms — Production by marine plants — Transfer of nitrogen from the sea to the land — Destruction of nitrogen compounds in the sea — Denitrification in the sea — Density of life in polar and tropical seas — Circulation of inorganic food-stuffs — Structural and current metabolism 273

CONTENTS Xlll

APPENDIXES

PAGE

I. Chemistry of the primitive ocean 299

II. Composition op deep-sea deposits 304

III. Four Hensen net hauls in the Irish sea .... 305

IV. Accuracy of quantitative plankton observations . . 306

V. Calculation op the coefficients of the quantitative

PLANKTON NETS 313

VI. Calculation of the age of the earth from the rate op

DRAINAGE OF SALT FROM THE LAND 315

VII. Bibliography 316

Index 320

ILLIJSTEATIONS

Chart of the British Plateau and Norwegian Sea . . ' Frontispiece

FIG. PAGE

1. The Lucas automatic sounding machine .... 4

2. The stop-cock sounding lead 6

3. Deep-sea reversing thennometer, Kiel hydrometer . . 8

4. Nansen-Pettersson water-bottle 9

5. International Fishery Investigation area .... 15

6. Naturalist’s dredge 16

8. Otter trawl-net 19

9. Arrangement of trawl gear 20

10. Agassiz trawl-net 23

11. Sea-bottom fishing basket 24

12. Ordinary surface tow-net . . . . . . . 26

13. Heligoland “ Scherbrutnetz ” 27

14. Sea-bottom deposits -35

15. Hydrographic section shewing temperature over the Wyville-

Thompson Ridge . . . . . . . . 39

16. Similar section shewing salinities 40

17. Chart of North-Western Ocean shewing the European

Stream and its oflfshoots . . . . . . . 47

18. Plankton : fishes, worms, etc. ...... 68

19. Plankton : Crustacea . . . . . . . . 71

20. Plankton : protozoa, etc. 76

21. Plankton : diatoms 79

22. Succession of fish ova in the plankton of Cardigan Bay,

1905-6 95

23. Rough succession of plankton in the sea off N.W. England . 96

24. The vertical quantitative plankton net . . . .- .122

25. The Hensen “ Filtrator ” . . . . . . '. 125

27. The “ Stempel-pipette ” 133

28. Distribution of plankton in the North Atlantic in the

summer to face p. 152

29. Distribution of plankton in the North Sea in January, 1897

to face p. 156

30. Variation of plankton and silicic acid in Kiel Bay . . . 237

31. Forms of bacteria 256

Chapter I. The Exploration Of The Sea

When, in December 1872, the Challenger left Portsmouth on her memorable voyage methods of oceanographical discovery were very imperfectly developed and what was then known of the physics and biology of the deeper seas of the earth was neither very exhaustive nor exact. There had indeed been many voyages of discovery in the course of which researches other than purely geographical ones had been attempted, but it was only a few years previous to 1872 that what we now recognise as oceanographical investigation had been contemplated as an end in itself Such a colossal task as a systematic survey of the oceans of the globe might usefully have been preceded by a preliminary study of the apparatus and methods of the earlier cruises, and by some extensive experiments applied to the perfection of these. This, however, was not done and the ship left England on her three years’ voyage with an equipment containing little that was novel. But the expedition was planned out spaciously, the ship was powerful and commodious and her naval and civilian staff were efficient in the highest degree. The apparatus was thus tested in every possible way and an invaluable foundation was laid for later improvement.

About a dozen oceanographical cruises of first rate importance have been made since then and almost every detail of the Challenger equipment has undergone refinement and improvement.

J. F.

A perusal of Chapters II and III of the Narrative of the Voyage, and a comparison of these with an account of the latest voyage of discovery will reveal many improvements in details of apparatus and general methods. Nevertheless there is little essential change. The Challenger voyage was so prodigious an advance on anything that had previously been attempted that a corresponding amount of progress will be difficult to attain. If we except the modern quantitative method of attack on problems of marine biology there is little in the aims and methods of any of the latter-day expeditions that is not indicated in the instructions issued by the Admiralty to the Challenger staff. The ship proceeded on her three years’ voyage without haste : she sounded, trawled, dredged and tow-netted, and when she returned a number of English and foreign specialists leisurely investigated the collections made, and collated and studied the data obtained. All this remains except the leisure : the modern expeditions sound, trawl, dredge and tow-net, just as the Challenger did, but with improved gear. To complete the parallel the famous Challenger Report still remains as the model on which all subsequent ones have been made.

The Challenger methods and apparatus have now acquired immortality in the cheaper text-books and I hope to acquire merit by^ refraining from their further description. A glance over the publications of the expeditions of the last thirty years reveals a host of improved forms of oceanographical apparatus. Every one of these cruises has added a new modification of some apparatus and has tacked on to it the name of some member of its staff, so that a catalogue of oceanographical gear would also be a list of the names of those who have taken part in this kind of discovery. For a description of all this apparatus encyclopediac limits would be necessary. How then is a conscientious author to indicate the progress made in this field ? This chapter is, however, only intended to serve as an introduction to a more special aspect of marine study and therefore a somewhat cursory survey of the apparatus of oceanography will suffice.

The fundamental gear of the science are the sounding machine, the thermometer, the salinometer or its equivalent, the trawl and dredge, and the tow-net. This order is a logical one, since

THE EXPLOKATION OF THE SEA

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biological enquiry, so far as it is not a mere catalogue of the names, characteristics, and distribution of organisms, is to be based on the results of physical investigation.

The sounding machines. The names of these are legion. But when the industrious reader wades through the descriptions of those of Brooke, Baillie, Belknap, le Blanc, Massey, Sigsbee, Tanner and Thomson (to take only a selection in alphabetical order) he will find it convenient to consider only the latest — the Lucas automatic sounding machine — for this possesses merits which render it unnecessary (at least for our present purpose) to consider the others. In it are the characteristics of the best type of English machinery — elegance, simplicity, compactness and efficiency. Its evolution is the result of commercial enterprise. So long as a knowledge of the depths of the sea was a purely scientific study the ability and expense expended on effort to obtain it were restricted within obvious limits. But when the acquisition of this kind of knowledge became an “ economic problem ” invention galloped. When it became necessary to obtain an exact knowledge of the contour of the bed of the sea for the purpose of laying telegraph cables, the modern sounding machine came into existence. When further it became a matter of some considerable expense to stop an ocean liner on her voyage in order to obtain a sounding, the “depth-indicator” was soon evolvedh

A “deep-sea” sounding may be regarded as one taken in water of over 200 metres in depth. To make this rapidly and exactly, and at the same time to obtain a sample of the deposits on the sea floor, is essential. Of necessity a very long sounding line is required, and this must be carried down to the bottom very quickly so that the line remains vertical. To do this a heavy sounding lead is attached to the end of the line, and obviously the latter must be strong enough to carry the weight. Yet the line must not be too heavy for it would otherwise possess in itself a very considerable mass. Now a thin line may be employed which will carry the lead when the latter is descending,

* In the depth-indicator a glass tube, open at one end, is lowered to the bottom. Water rises into the tube compressing the air. The depth is estimated by the application of Boyle’s Law.

1—2 but when the line has to be hauled again its weight, plus that of the sinker, may conceivably be great enough to break the line. A further necessity of the line is that it should not offer much resistance to the water on descending or hauling. Again, the sounding machine must be so constructed as to stop automatically when the bottom is reached, and there must be a means of recording the length of line run out — that is the depth of the sea in the place sounded.

In the Lucas, as in all other modern sounding machines, the line is a pianoforte wire which is usually less than one millimetre in diameter. This is polished so as to offer little resistance to the

Fig. 1. The smaller Lucas sounding machine. By kind permission of the Telegraph Construction and Maintenance Company.

water in descending or hauling. The line is wound on a reel from which it runs out over a wheel which has a counter recording the number of revolutions, and therefore the number of fathoms, since the diameter of the wheel is known. This arrangement is shewn in Fig. 1, which represents the smaller Lucas machine.

CH, l]

The recording wheel is attached to a movable arm which is connected with the frame of the apparatus by two coiled steel springs. When the weight of the sinker is on the wheel the arm is extended stretching the springs. This releases a brake which acts on the reel containing the line, so the latter runs out freely. But immediately the sinker touches the sea bottom the weight is taken off the arm and the springs pull the latter back while the forward movement of the base of the arm tightens a brake which lies close against the rim of the reel, whereupon the latter is stopped. The counter is then read and the depth of the sea is obtained.

The old-fashioned sounding lead of the mariner is a lead cone of about 7 to 30 pounds in weight. Remember that a very heavy weight is necessary to carry the line down rapidly to the bottom and prevent the latter from being thrown into coils or kinking. But when we add to the weight of the sinker that of the sounding line there is a very considerable strain on the latter and this is enough to break any line of manageable dimensions when a deep sea sounding is being taken. It is therefore necessary to devise some means whereby the weight, when it has served its purpose of carrying the line to the bottom, may be released and fall off, when the latter can then safely be reeled up again. All sounding leads are constructed with this object and all are modifications of that first devised by “ Passed Midshipman John M. Brooke of the U. S. Navy.” I describe here the latest form, the Sondeur a Clef” of the Prince of Monaco.

This is shewn in Fig. 2. It consists of a gun-metal tube furnished with a stop-cock at its lower end. The handle of the latter is a lever which, when the cock is closed, fits into a depression cut in the side of the tube. When the cock is open this lever stands out at right angles as is shewn in Fig. 2 on the left. The opening of the stop-cock is of the same bore as the tube. At the upper end of the latter is a plunger which can move up and down for a short distance — the latter being regulated by a slot cut in the sides of the tube in which work pins attached to the plunger. The sounding line is attached to the plunger and on the sides of the latter are two notches. When this plunger falls down within the tube the notches sink below the rounded upper end of the latter. The sounding tube itself is comparatively light and the weights (which may be 20 lbs. each) are slung on to the notches in the plunger. It is these weights which carry down the sounding line. Their total mass varies with the depth of water.

Fig. 2. The stop-cock sounding lead of the Prince of Monaco. There are several forms and that figured is described in the Campagnes Scientifiques, pp. 14 and 15. On the left the sounder is shewn descending, and just touching the bottom. On the right the sounder is shewn ascending. The weights have been released ; the tube is full of the bottom deposits and the stop-cock is closed.

When the apparatus is to be used one or more weights cast iron rings — are slipped over the outer tube, and the whole thing

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being suspended these rings are secured to the lead by means of a sling which passes over each of the notches in the plunger. It will easily be seen that when the lead touches the bottom the tension of the line decreases and the plunger drops within the tube. When the notch in which the sling is placed falls below the opening of the tube it releases the weights, which then drop off and are lost. But in falling off they push down the lever of the stop-cock which then closes. The tube has however been pushed down into the sea floor and is filled with a sample of the deposit there, and the closing of the cock prevents this from falling out when the line is hauled up again.

The water sample bottle and the thermometer. A simple sounding thus gives us a knowledge of the depth of the sea and also a sample of the deposits lying on the sea floor. A “ hydrographic sounding ” gives us a sample of the sea water at the bottom or at any required depth, and in addition the temperature of the water in situ. The water sample is to be used for the determination of the density, salinity, gas contents, or any other property or constituent of the water. There are a host of water bottles (Buchanan, Ekman, Jacobsen, Kidder-Flint, Meyer, Mill, Regnard, Sigsbee, Wille, and probably others). It will serve the reader best if I describe only the water bottle which is used by the vessels of the International Fisheries Investigations, and which was devised by Nansen and Pettersson.

This instrument is represented diagrammatically in Fig. 4. It consists essentially of two brass rods connected together at either end, and between which slides an open cylinder, which is the actual bottle. Fixed between the lower ends of these rods is a stopper which can accurately close the lower end of the cylinder; and sliding freely on the rods above the cylinder is another similar stopper which can close the upper end of the bottle. The wall of the latter consists of four concentric cylinders of metal and ebonite alternately : each stopper consists of a metal cap carrying three rubber discs and it is the latter which fit into the open ends of the bottle. The upper stopper is perforated to receive a thermometer, and the lower one is provided with a stop-cock. When the bottle is about to be lowered into the sea the parts are

A

Fig. 3. A. The Negretti and Zambra deep-sea reversing thermometer. The messenger is lowered down the line, strikes the catch C which then lifts the rod R from a depression in the thermometer case. The latter then turns over or reverses, breaking the mercury thread in the thermometer. B. The most recent deep-sea reversing thermometer (Richter’s pattern). C. A Kiel hvdrometer

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fixed in the position shewn by means of a spring catch not shewn in the diagram. The whole is attached to a steel wire rope and when it has been lowered to the desired depth a “ messenger ” is allowed to slide down the line until it strikes against the catch, when the cylinder slides down the rods until it is closed by the

Fig. 4. The Nan sen-Pettersson water bottle. Some parts are omitted. A.Aarethe stoppers ; B the concentric walls of the bottle ; C the outer case of the latter ; D, D, D, D the ends of the stoppers and the bottle, these parts slide on the brass rods R ; T is the stop-cock through which the water sample is withdrawn ; Th is the thermometer, and W the weight which carried down the apparatus.

lower stopper: at the same time the upper stopper also slides down the rods and closes the upper end of the bottle. Two spring catches shewn at the sides then make fast the whole apparatus. A sample of water at the depth to which the bottle is lowered thus fills the cylinderh

The bottle therefore collects a sample of water and isolates this in a central chamber surrounded by three concentric shells of water at the same temperature as that of the sample. These shells of water insulate the sample, preventing the conduction of heat from without, if, as is usually the case in a deep water sounding, the water from the deep has a temperature which is u,bove that of the water strata through which the bottle has to be hauled in coming to the surface. The same sounding therefore enables us to ascertain the temperature of the water while collecting a sample for further study.

The determination of the temperature of the sea is obviously a simple matter when it is the surface layers which are being investigated. All that is necessary is to lower a bucket Over the ship’s side, fill it, and then immerse a thermometer in this. Obviously the sample must be collected from such a situation that it is not contaminated by the discharge from the engine-room or from any exit-pipe from the interior of the vessel. But when a temperature has to be taken from a water layer which is at some distance from the surface the procedure is much more complicated. In the time of the Challenger the only means of obtaining this value was by the use of a “ slow-reaction ” thermometer, by using a maximum and minimum thermometer, or by using a reversing instrument. There were indeed other ingenious methods of obtaining deep-sea temperatures, such as by the electrical thermometer of W. Siemens. This depended on the fact that the electrical resistance of water varies inversely with the temperature. If then we balance the resistance of the water in situ with that of a sample of water on board at a known temperature by means of a Wheatstone bridge the problem is solved. But this method demands delicate apparatus not easily managed in a ship tossing in a seaway, and as a practicable means of obtaining deep-sea temperatures it has now been abandoned. The slow-reaction

^ The water-bottle ia described in detail in Publication de Circonstance of the International Council for the Exploration of the Sea, No. 21.

CH. l] THE EXPLORATION OF THE SEA 1 1

thermometer was one in which a long time was required for the instrument to indicate the temperature of the medium in which it Avas placed. Therefore in hauling it to the surface the temperature did not greatly change and the time increments of change could be calculated. But a practical objection was the time required to make an observation. So this method also has been abandoned. Finally we have the reversing thermometers, and these are still used. The instrument of this class originally made by Negretti and Zambra, Fig. 3, is too well known to require description. We have a thermometer tube which is constructed in much the same manner in which a clinical thermometer tube is made, that is the bore of the tube immediately above the bulb is bent twice in an S-shaped curve and is greatly contracted at this point. In a clinical thermometer the thread of mercury breaks when the instrument is taken out of the place the temperature of which is desired, and when the metal contracts with the reduction of temperature. The mercury in the capillary tube therefore remains where it was. In a deep-sea thermometer in which this principle is adopted the case carrying the tube is reversed when the desired depth is attained, this being done usually by a small propeller in the outer frame of the instrument which revolves immediately the direction of movement of the machine is changed on being hauled, and then releases a catch which allows the tube to reverse. The mercury then falls to the other end of the tube and as that latter is graduated from this end the temperature is recorded. In the Nansen-Pettersson water bottle a reversing thermometer is usually attached to the frame of the instrument and is reversed when the messenger springs a catch at the same time as closing the bottle. But since the thermometer enclosed in the central chamber of the bottle takes the temperature of the water in situ, and since this sample of water does not change greatly in temperature because it is surrounded by a practically non-conducting material, the indications of the reversing instrument are only used as a check on the other. The sample of water obtained by the Nansen-Pettersson bottle does actually change in temperature as the instrument is being hauled through water of a temperature markedly different from that to which it has been lowered, but the change is very slight and can be allowed for.