Transcriber’s Note
1. Certain typographic errors & hyphenation inconsistencies were
silently corrected.
2. The text version is marked up as follows:
(a) italics are indicated thus _italic_;
(b) small-caps are indicated thus +Small-Caps+;
(c) Images are indicated as [Illustration: (with narration.)]
3. Illustration captions have been standardised.
4. Table of Contents extended by adding references to the LIST OF
ILLUSTRATIONS, INDEX, and ADVERTISEMENTS.
[Illustration: _Frontispiece._
+A Jelly-fish with the fry of the Horse-mackerel.+
(The fish have been relatively very much enlarged.)]
THE
STORY OF LIFE IN THE SEAS
BY
SYDNEY J. HICKSON, D.Sc., F.R.S.
_Professor of Zoology in the Owens College, Manchester_
_WITH FORTY-TWO ILLUSTRATIONS_
LONDON
GEORGE NEWNES, LIMITED
SOUTHAMPTON STREET, STRAND
1898
OUTLINE CLASSIFICATION
OF
ANIMALS MENTIONED IN THIS BOOK.
PROTOZOA {Foraminifers.
{Radiolarians.
PORIFERA Sponges.
{Sea-anemones.
CŒLENTERATA {Corals.
{Jelly-fish.
{Many of the Zoophytes.
{_Asteroidea_ Star-fishes.
ECHINODERMA {_Echinoidea_ Sea-urchins.
{_Crinoidea_ Sea-lilies.
{_Holothuroidea_ Trepangs.
PLATYELMIA Flukes, Tape-worms, Planarians.
CHÆTOPODA Segmented Worms and Gephyreans.
{ {Copepods.
{ {Barnacles.
ARTHROPODA {_Crustacea_ {Shrimps.
{ {Crabs.
{_Insecta_ Halobates, &c.
{_Lamelli_ Bivalves.
{ _branchiata_
MOLLUSCA {_Gastropoda_ Whelks, &c., and Pteropods.
{_Cephalopoda_ Octopuses, Cuttlefishes, &c.
TUNICATA Sea-squirts, Salps, Pyrosoma.
{_Pisces_ Fish.
{_Amphibia_ Frogs.
{_Reptilia_ Turtles, Crocodiles, Snakes.
VERTEBRATA {_Aves_ Birds.
{ {Whales, Porpoises.
{_Mammalia_ {Seals,
{ {and the terrestrial Mammals.
PREFACE.
The story of the life of animals and plants in the sea is one with so
many aspects, that it is difficult to choose the points that may be
included, and those that may be omitted from a book intended for the
general reader. To some the story of the food Fishes and the Whales is
of the greatest interest; to others the beautiful shapes and colours
of shells have a predominating fascination; and to those who have
devoted themselves to geological study, the history of the animals that
contribute to the formation of the reefs and the ocean-bed present
features of special attraction. To many, then, the perusal of my book
must lead to disappointment as no one of these aspects has been treated
adequately; but if some new interest is awakened, some new train of
thought quickened into life, one of the objects I had in view will have
been gained.
The book is only intended to be a sketch of some of the most important
lines of scientific researches which are now being pursued by
zoologists in many parts of the world. Discoveries, which are of the
deepest interest to all intelligent minds, are in many cases described
in books and periodicals that do not come within the reach of the
general public. I have tried, therefore, to collect some of them into
a small compass and describe them in language which I trust will be
intelligible to those who have not been trained in the alphabet of
zoological technicalities. The use of some long words was unavoidable,
but I have endeavoured to explain them adequately either in the text or
in the index.
Some of the illustrations have been copied from the works of other
Naturalists, and the sources from which they came are acknowledged in
the list of illustrations; but the majority of them have been drawn,
specially for this work, from specimens from the Manchester Museum or
my own collections.
SYDNEY J. HICKSON.
_November 1897._
CONTENTS.
CHAP. PAGE
LIST OF ILLUSTRATIONS 8
I. OCEANOGRAPHY 9
II. SHALLOW-WATER FAUNA 23
III. SHALLOW-WATER FAUNA OF THE TROPICS 55
IV. SURFACE-SWIMMING FAUNA (INVERTEBRATES) 82
V. SURFACE-SWIMMING FAUNA (VERTEBRATES) 118
VI. DEEP-SEA FAUNA 135
VII. COMMENSALISM AND PARASITISM 146
VIII. THE ORIGIN OF THE MARINE FAUNA 172
INDEX 180
ADVERTISEMENTS 184
LIST OF ILLUSTRATIONS.
ILLUSTRATION PAGE
_Frontispiece._--A Jelly-fish with the fry of the Horse Mackerel
(from specimens captured by Mr F. W. Gamble off Valentia). 2
Fig. 1--Globigerina Shell 21
Fig. 2--Radiolarian Shells 22
Fig. 3--Common Pipe-fish (from Royal Natural History) 25
Fig. 4--Phyllopteryx (from Royal Natural History) 26
Fig. 5--Diagrams of Eyes 27
Fig. 6--A branch of the Zoophyte Obelia 30
Fig. 7--Medusa produced by Obelia 31
Fig. 8--A Bivalve Mollusc 35
Fig. 9--The common Sole 37
Fig. 10--The Angler (from Royal Natural History) 38
Fig. 11--Vertical section of a Balanus (after Claus) 40
Fig. 12--Nauplius larva of a Balanus (after Groom) 41
Fig. 13--Sea-urchin 43
Fig. 14--Smooth-shelled Gastropod 47
Fig. 15--Spiny Gastropod 47
Fig. 16--A Cuttle-fish 49
Fig. 17--The Wrasse 51
Fig. 18--The John Dory 54
Fig. 19--Polyp of a Madrepore Coral (after Fowler) 58
Fig. 20--Chætodon 62
Fig. 21--Globe-fish 64
Fig. 22--Stereosoma 67
Fig. 23--Coral-reefs 69
Fig. 24--Periophthalmus 74
Fig. 25--Free-swimming Copepod (after Claus) 88
Fig. 26--Swim-bladder of Velella 96
Fig. 27--Solitary form of Salp 99
Fig. 28--Pteropod 101
Fig. 29--Shells of Foraminifers 104
Fig. 30--Globigerina 105
Fig. 31--Young larva of a Star-fish 111
Fig. 32--Pluteus larva 113
Fig. 33--Long-spined Barnacle-nauplius (after Chun) 116
Fig. 34--Sun-fish 122
Fig. 35--The common Porpoise 129
Fig. 36--A deep-sea Fish (after Filhol) 139
Fig. 37--Hermit-crab and Sponge 149
Fig. 38--Section through a Sponge showing Hermit-crab 150
Fig. 39--A Trepang 153
Fig. 40--A Crab-gall 158
Fig. 41--A parasitic Copepod 169
THE STORY OF LIFE IN THE SEAS.
CHAPTER I.
OCEANOGRAPHY.
One of the most important facts that has been established by modern
investigations of the Sea is that there is no region in its vast extent
that is entirely devoid of animal life. The surface waters in the
Equatorial calms and the ice-cold waters between the ice-bergs of the
Arctic regions are densely populated by animals, large and small; the
heavy and heated waters of the Mediterranean and Red Seas, and the cold
and comparatively fresh waters of the Norwegian fjords, the shallow
waters of the coasts and the greatest depths of the ocean-beds all
present us with their characteristic forms of living creatures. There
is no Azoic region known to us. Wherever we use the trawl or dredge
we may expect to find some representatives of the various classes of
marine animals. But the seas exhibit so many varying conditions that,
as we might have expected, the animals that characterise one region are
absent from another; and while, in some places animal life is abundant,
in others it is very scarce; just as on land we find the grass-lands
and forests teeming with life, and the great deserts and mountain tops
inhabited only by a few solitary Lizards, Birds or Insects.
In order that we may fully understand, then, the nature of the problems
concerning the distribution of animals through the seas, it is of
importance to consider first the conditions under which they must
live in the different parts of the ocean. A knowledge of geography is
clearly necessary for those who study the distribution of terrestrial
and aërial animals, and equally necessary is it for those who wish
to learn something about the distribution of the aquatic animals,
to consider first of all the rudimentary principles of hydrography.
The principal Sea areas of our globe may be roughly divided into two
groups: namely, the great oceans--the Atlantic, Pacific and Indian
Oceans--and the Inland seas, which are partly enclosed by land, such
as the German Ocean, the Mediterranean Sea, and the Red Sea. Taking
the areas of the great oceans and the seas together, we find that no
less than 141 millions of square miles, or nearly three-quarters of the
surface of the globe, are covered with water. Moreover, these great
areas are continuous, so that it would be possible for an animal, other
conditions being favourable, to pass from any one sea, such as the
Black Sea, to any other, such as the Hudson’s Bay, without leaving the
water,--an important fact in the consideration of the distribution of
marine forms of life.
The depth of the sea varies very considerably in the different parts of
the world. In the inland seas the water is comparatively shallow, but
in the great oceans it is very deep. In the middle of the North Sea,
for example, we should not expect to find a depth much exceeding 250
fathoms, but in the Atlantic or Pacific Oceans we have to pay out more
than 2000 fathoms of the sounding-line before the bottom is reached. In
some parts of the ocean-basins a few very deep holes or furrows may be
found in which the depth exceeds 4000 fathoms, or 24,000 feet. One of
these deep holes occurs in the Atlantic Ocean, a little to the North
of the Virgin Islands in the West Indies, and there is another in the
Pacific Ocean close to the coast of Japan; but the greatest depth that
has yet been found is one recently discovered by H.M.S. “Penguin” off
the coast of New Zealand of over 5000 fathoms. Apart, however, from
the fact that these very great depths are only of local occurrence,
the areas of deep water--that is, of more than 2000 fathoms--are so
much greater than the areas of shallow water, that when we make a
calculation of the average depth of the sea we find it is no less than
2100 fathoms, or 12, 600 feet.
The temperature of the sea is another feature which undoubtedly
influences very greatly the character of its Fauna. The main source of
the heat of the sea is the sun--for the heat derived from submarine
volcanoes must be comparatively so small that we may omit it from
consideration. Consequently we find that in the Equatorial regions the
surface waters of the ocean are warmer than they are in the Temperate
regions. These, again, are warmer than in the Arctic circles. But
water is well-known to be a bad conductor of heat, and therefore
the direct influence of the sun affects only the most superficial
layers. In the Equatorial region of the Pacific Ocean, for example,
the surface temperature is sometimes as high as 80° Fahr., at 100
fathoms from the surface it is only 60°, at 400 fathoms only 45°, and
at 1000 fathoms only a few degrees above freezing point. On the land
the temperature falls as we pass from the coast to the high plateaux
and mountains, and we find snow-capped mountains in Central Africa just
as in Switzerland or Norway. In the sea the temperature falls as the
thermometer is sent deeper from the surface. Just as on the land the
snow line of the mountains is reached at high altitudes in the Tropics,
at lower altitudes in the Temperate regions, and in the Arctic circle
at the level of the sea, so in the sea the cold water that is found 500
fathoms below the surface in the Tropics, reaches a higher level in the
Temperate regions, and is at the surface in the Arctic circle.
There is however one important point of difference between the
distribution of these low temperatures on the land and in the oceans,
in that they are broken in the former, and continuous in the latter.
If we were to imagine an aquatic animal that could only live in
temperatures below 35° Fahr., it would be able to travel below the
surface from one pole to the other, or from one ocean to another; but
it would be impossible for a terrestrial animal, exhibiting the same
peculiarity, to leave the Arctic circle or the Alpine region without
traversing lands where the temperature is higher than that which is
necessary for its existence. It might be supposed from what has just
been said that the temperature of the water at the bottom is constant
for the same number of fathoms of depth. This is not, however, the
case. The temperature of the sea-bottom of the great ocean-beds is
approximately the same, varying from 28° F. in the Atlantic to 35°
F. in the Pacific; but in places where main basins occur, surrounded
on all sides by shallower ridges, the temperature of the bottom of
the basin is the same as that of the lowest ridge. For instance, the
temperature of the bottom of the Sulu Sea, lying between Borneo and
the Philippines, is 40° F. at a depth of over 2000 fathoms. Again, the
temperature of the Red Sea is as high as 70° F., although depths of
1200 fathoms occur in its central portions; and this is the same as the
temperature at the Straits of Babel Mandeb, which are 200 fathoms deep,
and form the only outlet to the open ocean. These facts probably cause
considerable modification in the character of the animals inhabiting
such enclosed basins, but further investigations are needed before we
can arrive at any very definite conclusions in the matter.
Another important element that must be taken into consideration in
studying the environment of marine animals, is the quantity and
character of the salts held in solution by the sea-water. In the first
place we must remember that the sea-water normally contains a far
greater percentage of salts in solution than the water of rivers and
lakes, and this causes it to be very much heavier. If a tumbler be
half filled with sea-water, upon which some fresh water is slowly and
carefully poured, there will be for some time very little mixture of
the two fluids, the heavier sea-water remaining at the bottom, and the
lighter fresh water at the surface. Now the density of the sea-water,
or in other words the amount of salts in solution, is not the same
over the whole world, and the differences that may be observed in
this respect are due, in most cases, to the simple physical principle
just enunciated. If we could imagine a river pouring its waters into
a perfectly calm, tideless sea, we should be able to trace the fresh
river water far away from the coast, for it would simply float on the
heavier sea-water without mixing with it to any appreciable extent. In
most cases, however, the tidal-waves, rushing up and down the river
estuaries, stir up the fresh and salt water together, and cause a very
considerable mixture, so that the water becomes either distinctly salt
or brackish. Where very large quantities of fresh water are poured
into the ocean, as, for example, at the mouth of the Amazon or the
Mississippi, the surface water remains so fresh that the salt taste
can hardly be appreciated at a distance of some miles from the coast.
This fact sufficiently indicates the influence of great rivers upon the
density or saltness of the sea-water in their neighbourhood, and the
reader will be prepared for the statement that many inland seas, such
as the Black Sea, are appreciably less salt than the great oceans.
Again, the ocean water itself is not of the same density in all
latitudes. In regions where there is a copious rainfall and the sea is
not frequently disturbed by severe storms, the rain takes some time to
mix with the heavier salt water on which it falls, and consequently
there may always be discovered in these localities a thin stratum of
comparatively fresh water on the surface of the ocean. In some inland
seas where there is considerable evaporation and a slight rainfall, as
for example, the Red Sea and the Mediterranean, the sea-water reaches
an even higher degree of concentration than it does in the open ocean.
The following table will serve to illustrate these facts:--
Density of rain-water, 1·00.
Density of the Black Sea surface, below 1·025.
Density of the Atlantic Ocean surface (west of the Canaries), 1·0275.
Density of the Mediterranean Sea, over 1·028.
Density of the Red Sea, 1·030.
Density of the bottom water of the Atlantic, 1·029 (west of the
Canaries).
That the rate of movement of the water influences very largely the
character of the animals that live in it, is a fact that it is not
necessary to discuss fully in this place; but as it is undoubtedly one
of the factors which must be taken into consideration in discussing the
character and possible origin of the Fauna of any particular region,
a brief survey must be given of some of the principal causes of the
movements of the water and the characters of the tides and currents
which are manifest in the sea. Twice every twenty-four hours the water
of the sea rises and falls. This movement is due to the attracting
influences of the sun and moon, and is, as is well-known, greater when
the moon is full and when it is new than at the intermediate times. If
the distribution of land and water on the surface of our globe were
different, and a free waterway occurred round the world, right in the
Equatorial band we should probably find a double tidal-wave rushing
round the earth every twenty-four hours. As it is, however, the great
tidal-wave is checked by the continents, and as it approaches the
coasts is retarded and diminished in force. In Archipelagoes and along
broken coast lines the tidal-waves produce true surface currents, which
frequently run with great rapidity and exert considerable corroding
action upon the rocks. In many estuaries and bays the tide rushes in
with such force that the water is heaped up to a great height against
the land. At the entrance to the Bay of Fundy, for example, the rise
at spring-tides is no less than 70 feet, and at the Cardiff docks the
difference of level between high and low spring-tides is 42 feet. The
tumultuous ebb and flow of such masses of water along the coast is
fatal to some forms of animal life and favourable to others, and so to
some extent it modifies the character of the Fauna.
In addition to the surface currents of the coast, produced by the
tidal-waves, there are also the true ocean-currents, which must be
briefly considered. They are caused by the winds which blow constantly
in a definite direction across the oceans. The prevailing winds not
only raise the sea into waves, but drive the superficial layers of the
water over the subjacent layers in one direction. In studying a map
of the great ocean-currents, we notice a well-marked one lying to the
North of the Equator in both the Atlantic and Pacific. This flows from
East to West and follows very closely the lines of the prevailing winds
in that region. Similarly in the temperate regions of the Southern
Hemisphere there is an ocean-current, flowing however in this case in
the opposite direction--from West to East--and so corresponding with
the trade-winds of that part of the world. The well-known Gulf-stream
of the North Atlantic, although modified in some respects by other more
complicated causes, also follows for part of its course the general
direction of the prevailing winds.
The currents just described are surface currents only, and do not
affect to any great extent the mass of the subjacent waters in the
ocean-basins. It is difficult to estimate the depth to which their
influence reaches, but it is not probable that it extends more than 200
fathoms below the surface. In addition to these, there is also a series
of slow currents in the deep waters flowing in definite directions.
In the Tropical regions the waters are constantly being heated by the
sun, and passed away by the trade-winds to the North and South and
ultimately towards the poles. In their long and complicated journey
they are gradually cooled down until, in the regions of the ice-bergs,
they reach a temperature just above the freezing point of sea-water.
Here the water, being colder and therefore heavier than that of the
other regions of the world, sinks to the bottom, and gradually returns
in a deep-seated mass towards the Equator, where, welling up from the
bottom, it replaces the heated layers of the surface. It is almost
impossible to determine with accuracy the rapidity and exact direction
of these deep-sea-currents. It is extremely probable that they are
immensely modified by the irregularities of the bottom and the outline
of the coast banks, but their exact topography must remain for the
present one of the secrets of the abyss that are not revealed to us.
All that can be said is, that the warm surface water which passes from
the Tropics towards the North and South is replaced by deep-seated
Polar currents, which account for the extremely cold water that is
found at great depths in the ocean-basins, and also for some of the
peculiarities of the marine Fauna, which will be referred to later on.
The character of the sea-bottom in various parts of the world must
be referred to before passing on, for there can be little doubt of
the important effect it has upon the Fauna. In the neighbourhood of
continents the bottom of the sea varies very considerably. The great
rivers bring with them in suspension the products of the wear and tear
of mountains and valleys; the coast line, washed by the continuous
ebb and flow of the tides, contributes some of its substance to the
formation of the sea-bottom; and the countless millions of animals
and plants of the shallow waters leave their skeletons and shells as
they die to form an integral part of the floor of the ocean. Thus
the sea-bottom in the neighbourhood of the land is formed partly
by terrigenous deposits, varying of course in character with the
geological nature of the land itself, and partly by the animal and
vegetable deposits of the coast. In some cases the deposits brought by
the rivers can be traced in the sea-bottom for a very great distance
from the coast. The characteristic mud of the Congo river can be traced
600 miles from its mouth, and it is said that the Arabian Sea and the
Bay of Bengal are carpeted for 1000 miles by the mud brought down by
the Ganges and the Indus. Leaving out of consideration, however, for
the moment the exceptional cases of such large rivers as these, we may
say that the influence of the land deposits upon the character of the
sea-bottom extends to a distance seawards of about 250 miles. If we
had a complete and careful survey of all the coast lines, it would be
possible for us to draw a line round the great continents marking the
limit of the deposits of river and coast mud. This line has been called
the mud-line by Mr John Murray, and, as he has clearly pointed out, it
is characterised by an abundant and extremely interesting Fauna.
The sea-bottom, then, within the limits of the mud-line, is very
largely composed of deposits from the land brought down by the rivers.
In some volcanic regions of the world this is, to a great extent,
augmented by lava and water-logged pumice, and in other districts by
the mud and stones dropped by the melting ice-bergs. The influence
of animals and plants upon the formation of the sea-bottom is often
very great indeed in shallow water, though it varies considerably in
different parts of the world. In the neighbourhood of the British
coast, for example, the sea-bottom is, in many places, carpeted with
the calcareous Sea-weed, _Lithothamnion_,--in other places the
dredge will come up crammed full of bivalve shells. But such instances
as these in which the floor of the sea is covered with animal or
vegetable shells, are comparatively rare and of small extent in the
neighbourhood of land in the Temperate regions, and in nearly all
localities the true terrigenous deposits can be readily obtained by
the use of a small meshed dredge. In the warmer regions of the world,
however, the sea-bottom in the shallow water is over great areas
completely covered by animal and vegetable products. In the West
Indies, and in some parts of the Eastern coasts of Tropical America, in
the Eastern Archipelago and the coast of East Africa and its islands,
Coral-reefs are found. These are entirely built up of the skeletons and
shells of animals, and a few Coralline Algæ. In the vicinity of these
reefs the floor of the sea is for miles carpeted with the broken-down
skeletons of these animals, sometimes in the form of a fine coralline
sand, sometimes of large lumps studded with knolls of living Corals,
Molluscs, Sea-urchins, and other creatures. We find, therefore, in the
warmer regions of the world immense areas of shallow water in which the
terrigenous deposits take but a very small part in the formation of the
sea-bottom, animal and vegetable life being so vigorous and active as
to be able to form enough shells and skeletons to cover every available
part of its surface.
[Illustration: +Fig. 1.+
Globigerina Shell from a deep-sea ooze.]
Far away from continental lands, and at great depths, the character
of the sea-bottom completely changes. At a distance of 100 miles from
the coasts of America or Europe, for example, the land deposits have
already found their resting-place, and the animal life in the depths of
the Atlantic is poor in skeleton-forming genera. However, the surface
waters of the ocean teem with creatures of all sorts which, as they
die, drop down their skeletons and shells in a gentle shower to form
a fine deposit on the bottom. When we get beyond the mud-line, then,
and use the dredging or sounding apparatus in depths of 1500 to 2500
fathoms, we find that the bottom is largely composed of the shells of
such surface animals as the Pteropods and Globigerinas, and according
to the relative abundance of these forms it is called Pteropod Ooze or
Globigerina Ooze. In still greater depths than these the character of
the bottom again changes, and we find a deposit which is commonly known
as the Red clay. The explanation of this change of character depends
upon the fact that sea-water exercises a slightly solvent action upon
carbonate of lime, and the shells of the Globigerinas and other forms
are, in seas of a depth of over 2500 fathoms, dissolved before they can
reach the bottom. The only shells that can survive this long journey
are the siliceous shells of the Diatoms and Radiolarians, and in those
parts of the ocean where these organisms live in abundance their empty
shells form an important percentage of the composition of the Red
clay. Over a very considerable area of the Pacific Ocean, however,
the Red clay contains only a minute proportion of these shells, and
its composition has given rise to a good deal of discussion among the
authorities. It may be considered to be a conglomerate of the horny
fragments of dead surface-living animals, of volcanic and meteoric
dust, and of small pieces of water-logged pumice-stone.
[Illustration: +Fig. 2.+
Radiolarian Shells from a deep-sea deposit.]
In some of the very deep holes of the Pacific Ocean the mud is
almost entirely composed of Radiolarian shells, and is then called
“Radiolarian ooze”: and in the Southern Sea a mud called Diatom ooze
has been found, which consists principally of the siliceous shells of
these minute algæ. Notwithstanding these varieties of the mud, and
others that space does not allow me to refer to at length, we may
suppose that if the floor of any one of the great oceans were exposed
it would have the appearance to a traveller of a vast desert-like
expanse, without a stone, a rock, or a cliff to vary the monotony of
the scene. At one time it was supposed to be an absolute plain, without
any important change of level from the mud-line of one continental
coast to the other; but the result of modern submarine explorations has
been to prove that in all the great ocean-basins, hills and ridges, as
well as troughs and deep holes occur, which break the monotony of the
generally smooth and level character of the bottom.