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Report

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The Danish Biological Station

to

The Board of Agriculture.

VII.

1697:

By

C. G. Joh. Petersen,
PhD:

oe Sne? ==

1898.

From

The Danish Biological Station.

VIET

LO veE

Kjøbenhavn.
Centraltrykkeri et.

1898.

'
AN

Plankton Studies im the Limfjord.
(With 1 Map and 4 Tables.)

By C. G. Joh. Petersen.

1897.

—— rt —4

While the Biological Station was at work in the Limfjord, at Nykøbing
on Mors, in 1895 and 96, the Plankton was often examined, and I was aston-
ished at the great difference in its appearance at the various times, a differ-
ence which was found also by a closer microscopic examination. In both these
years I had, in the autumn, observed an unquestionable immigration of Noctiluca
together with Pilema octopus (Rhizostoma Cuvieri), the latter in large, beauti-
ful specimens, and the former so numerous that, when it died and drifted
ashore, it would cover the coast with a red coating which looked like tomato-
soup. There can be no doubt that the two said organisms had drifted into the
fjord from the North Sea (in the Cattegat they are not so common); ordinarily
they do not live here: during the whole rest of the year they are not to be
found in the Limfjord. When we see the rapid current which at times, parti-
cularly with a westerly wind, runs through the whole fjord from the west to
the east, in some places almost like a river, we can easily understand such
an immigration; nor did I doubt that the changes which I found from time to
time in the finer plankton, particularly among the Diatomaceæ, must be ex-
plained in the same way, by an immigration with the current from the west or
from the east. It would be a good thing, however, to prove that this was really
the case, and I seized the opportunity to do so with so much the greater
pleasure, as another question in which I was interested might be solved at the
same time. This question concerned the density of the plankton in our fjords,
compared to its density in the Swedish and Norwegian fjords and in our more
open waters. By seeing Professor 0Ofio Pettersson carry out some plankton-
gatherings in the Gullmarefjord (later on also while travelling in Norway), I had
got the idea that our fjords were evidently much richer in plankton than those

of Scandinavia, and to prove this it was necessary only to make some casts
with one of Hensen's »quantitative« plankton nets in various places and com-
pare the weight or volume of the plankton I found with that from the open
waters. If this gathering took place from outside the western mouth of the
Limfjord, through the fjord, and ending in the Cattegat, I should see also
whether the plankton of the Limfjord agreed with that of the Cattegat or with
that of the North Sea at this moment, and thus learn whether it had come hy
the current from the east or from the west.

The result of such an investigation, undertaken onboard the gun-boat
31. October 1896, is seen in table I. The

Diatomaceæ and Peridimieæ are here determined by Mr. H. Gran, whom I

»Hauch« in the days from 22.

thank with all my heart for doing this work, a work which I value so much
the higher, as I know that he is one of the greatest authorities on this
subject. The letter r im the tables indicates that the organism in question is
rare, € that it is common, cc and ccc that it is very common, and + that it
is neither rare nor common. Mr. Gran has hitherto used these marks in this
way, but I confess that they are only of a very relative signification; and here
particularly, where the question is of somewhat quantitative determinations
of the whole mass of the plankton, other designations ought to be used in
future, which do not speak of »rare« or »common« without further determina-
tion and, indeed, without our knowing whether they mean »common« or »rare«
in the specimens which have been gathered or in the volume of water in which
they have been taken. I could imagine that we, by future investigations of
this kind, preferred to determine the occurrence of the plankton organisms
in the volume of water from which they are taken, only by the weight, in
gram, of the plankton, and confined ourselves, in our work with the specimens,
to give information of how great a proportion (in weight or volume) of the
whole mass that is gathered the various species form; one species forms about
half <of it, "one nearly the whole; one ”c. "1, "one ce. 71; one"e 11109; heretis
something, at any rate, in which the thought can rest, and I should think it
is as easy to do so, as it is to use the present designations.

For the preliminary orientation which I here wish to give, the designa-
tions used by Mr. Gran may be employed however, when we remember that
ce and ccc indicates an occurrence which is perhaps 100, nay 1000 times
greater than r.

As the table shows we made one excursion through the Limfjord in Octo-
ber—November 1896, another in April 1897 in the »Sea-eagle«, and finally a

third excursion in July 1897, also in the »Sea-eagle«, all three starting from the
North Sea oft Thyborøn, and continuing through the Limfjord; the numbers
at the top of the table (I) refer to the map, page 23. On our first and second
excursion we went into the Cattegat (Nr. 12—13), on the first even into the
Baltie Sea (Nr. 14 between Falsterbo and Stevns). The table further shows
how many fathoms we fished through (from the bottom to the surface); every-
where only vertical hauls were taken with the ordinary Hensen's plankton-bag,
with an opening of "/,, [] meter. On the first excursion we used a bag we
had borrowed from Hensen, on the second and third a bag of the same size,
made by ourselves, with one of Apstein's buckets underneath, instead of one
of Hensen's.. We made a comparison, however, between the fishing-power of
the two bags, the result of which showed that it was about the same. The
mass of the plankton was determined, during the first excursion, onboard,
simply by immersion in water in cc; on the two last excursions, after return-
ing home, by weighing it, in gram, the plankton having been kept in weak
spirit. The latter method is somewhat more accurate, if only the plankton is
dried equally much every time. This is pretty easily done, by filtering it
through a circular piece of silk gauze, which is then moved about on dry
filtering-paper, till it only just leaves a trace of moisture on the paper, in the
form of quite small separate points. The number of ce got by pressing away
the plankton turned out to be nearly corresponding to the number of grams
got by weighing; they are therefore both stated in the tables under the heading
of »Gram«. On the other hand it gives a considerable difference, whether the
fresh plankton is weighed in water or kept in spirit in this way, particularly
if the spirit is strong; but also this is, I think, of slight moment with regard
to the question with which we have here to do.

On our first excursion the salinity was measured by means of an aero-
meter in order to give some orientation also in hydrographie matters.

As above mentioned Mr. Gran has determined both Peridinieeæ and
Diatomaceæ. The latter he has divided into oceanic and neritic, and among
the neritic he has classed all species in which resting-spores have been found,
moreover also some rare species in which we may suppose that resting-spores
will be found, and finally 3 common ones: Skeletonema costatum, (Gwinardia
Jlaccida, and Leptocylindrus danicus. He says, however, that it is not always
easy to distinguish between neritic and oceanic Diatomaceæ with any cer-
tainty.

It would have been a good thing, if the plankton, all through, could

have been determined, particularly with respect to the animals; this, however,

[ss

has not been possible. The various larval forms of bivalves, snails, annelida,
echinoderms, which appear in it, are scarcely of any greater importance for, the
present investigation, however, and of other animals that may be said to be
common in the plankton gathered in, there are nearly only copepoda; these into
the bargain are all common species. To separate the animals from the plants in
the plankton, so that they might be weighed separately, is impossible. Cen
trifugalising has been tried, but with no success. If we want more than a
rough estimate, there is nothing left hut counting, as Hensen has introduced
it. I suppose that the number of animals, in general, is much less variable
than that of the plants (Diatomaceæ), a rule wich also Hensen emphatically
lays down.

Å glance at the table shows us that, on all three excursions, in October
1896 as well as in April and July 1897, the quantity of plankton in the North
Sea (1), in spite of the great depth which was fished through (83—9 fathoms),
is only 0,5— 1,5 gram, while in the fjord, where the water is not nearly so
deep, it most frequently is much greater, up to 16 and 27%) gram on a depth
of respectively 3 and 5 fathoms. I am sorry that four glasses, containing the
richest plankton belonging to the second excursion, have been broken on their
way home from Norway. Besides the measurements here stated I have a
great many more from the Limfjord from the first excursion, which I have
left out, however, to give a clearer view; they showed also that there was a
very rich plankton, particularly in the western part of the Limfjord, at the
stations 3—4—5—6—7, many times richer, or denser, than the plankton in
the North Sea. The smaller catches in the Limfjord, on the other hand, hail
from places as 7a in Hvalpsund, where the salinity is very low on account
of the rivulets which here fall imto the fjord, or from the long narrow eastern
part from Løgstør to Hals (stations 9—11), where the salinity is also lower
that at the western stations 4—7. Not even the Cattegat (see No. 12—13)
could, in October, boast such a great quantity of plankton per surface unit
as the western part of the Limfjord, and in the Baltic Sea there was scarcely
any diatom-plankton whatever at that time.

On the basis of the measurements before us, it may then be said that
the western part of the Limfjord in its main course (stations 3—7), from spring
till autwmn, at least at the three points of time when we studied it, had a plank-
ton whose weight per [] meter surface of the sea, even irrespective of the slight

=) These two numbers are the results of measurements of fresh plankton, and they
are considerably greater than they would have been, if we had weighed plankton that
had been kept for some time.

9

depth of the fjord, was greater than that of the plankton of the North Sea and in
the narrow eastern part of the Limfjord (stations 9—10). We cannot imagine,
therefore, or at any rate only with great difficulty, that this dense plankton
of the western part of the Limfjord, in its present form can have been carried
into the fjord by a current from the east; but ft is peculiar to the fjord on
account of its great density. It was not positively proved by this, to be sure,
that the plankton in the Limfjord is denser than in the Norwegian and Swe-
dish fjords, but only that it was of less density in the North Sea and Cattegat.
When one has seen, however, how transparent the water is in the deep Scan-
dinavian fjords, just as in the Skager Rack and the North Sea, one cannot
after this doubt any more that our shallow fjords have the densest plankton;
but they have such a plankton only at certain times of the year. (See later on.)
Å closer investigation of the component parts of the Limfjord-plankton shows
further (See the table) that other species are predominant here than in the
plankton of the North Sea or the eastern part of the Limfjord.

On our first excursion thus Chætoceros debile formed the main mass of
the plankton of the western Limfjord, but it was not found in the North Sea
where, on the other hand, R/rizosolenia styliformis was dominant. In the eastern
part of the Limfjord Cx. debile was quite rare, and the mass of the plankton
was here very insignificant. In the Cattegat, finally, quite, another diatom re-
placed it, viz. Rhizosolenia alata. The first station in the Limfjord (No. 2) was
very much like the North Sea, but it is here also that the water pours into
the fjord.

On the second excursion, station 2 also resembles the North Sea very
much; for the rest, it is strange to see that no peridinieae at all occur in the
fjord at this time of the year; they do not appear till we reach Nr. 11 immedi-
ately by the Cattegat.

On our third excursion, im July, we find peridinieae throughout the whole
fjord, and not a few dtatoms are found also in the North Sea, but the common
Chætoceros debile, Ch. contortum, and Skeletonema costatum do not occur there,
nor are they found in the narrow eastern part of the Limfjord.

As the weight of the plankton per [] meter showed us, so it is shown also
by the component parts of the plankton: the occurrence of the diatom-plankton in
the western part of the Limfjord cannot be explained simply by its pouring in
with the water from the North Sea or from the Cattegat; it must breed, in an
independent way, in the Limfjord, so that, as a rule, it has neither the same
density, appearance, or composition as the plankton in the neighbouring wa-
ters; it occurs, in short, as a peculiar diatom-plankton.

10

I have said that we cannot imagine — or that we can do so only with
difficulty — that the Limfjord-plankton, as it is different from that of the North
Sea, can have come from the North Sea in the form in which it occurs in
the fjord. For we could imagine this to be the case only, by supposing
that the plankton in the North Sea, every time the imvestigations were
undertaken, some days before had been like the Limfjord-plankton, but then
again had changed before the day of the investigation; this should have taken
place all three times. Nothing is known of such sudden changes in the plank-
ton of the North Sea; on the contrary, it has been proportionally very little
changed even at the different times of the year (See the table), so that it may
be left quite out of consideration that the plankton of the Limfjord on these
three excursions might be imagined to hail from the North Sea. But we might
imagine that some single specimens of all the species that occur in the plank-
ton of the fjord, though extremely few in number and therefore not observed
in these samples, are carried in from the sea, so that we might say that the
»germs« at any rate hail from the sea, whence they must come again every
year, carried in, consequently, by the current. The Limfjord then should
have the power to develop some species in great masses and to destroy others;
but it should not be able to develop any diatom-plankton whatever, if only
pure water without any diatom-»germs« poured into it. Although I do not
believe in this possibility, I must acknowledge it as such. The question may
be settled perhaps by germination experiments with the diatom-germs contained
in the bottom-clay of the Limfjord or in the North Sea water. Should it be
proved then that the water of the North Sea, which apparently contains but
a very meager »styli-plankton«, by being exposed only to somewhat changed
physico-chemical conditions (by getting mto the Limfjord) can change its
plankton, so that it must be characterized as a »didymus-plankton« (See later
on), then it shows that it is not so much the direction in which the volume of
water moves, which the plankton follows, as the physico-chemical conditions
of the volume of water itself, and that the plankton in an almost chameleonic
way can change its appearance.

With respect to the difference between the plankton in and outside the
Limfjord on our first excursion Mr. Gran says, that the North Sea has a »warm
north-Atlantic plankton with neritic North Sea forms in small quantities (Bid-
dulphia mobiliensis) = oceanic 'styli-plankton'«, while the Limfjord has a »ne-
ritic plankton with Chætoceros debile vastly predominant, and as subordinate
component parts Ch. didymum and Rhizosolenia setigera.« He says that »this
plankton might be called w%e Didymus-plankton of the Limfjord, if by this

11

designation we mean warm neritic harvest-plankton«. Also on the other
excursions he finds a great difference between the plankton of the Limfjord
and that of the North Sea. —

If the whole Limfjord had been formed by a series of brackish lakes
with stagnant water, I should not have been astonished to find a different
plankton in the different lakes; but when we see a current which generally
runs east, or which at any rate much oftener runs east than the opposite
way, enter through the western opening of the Limfjord and go on through
the whole fjord, with so great speed that the narrow parts remind us of slowly
running rivers, against whose current sailing vessels can but beat up with
difficulty, then we should think, certainly, that every trace of differences in
the plankton must disappear. We should expect the same result for all
organisms as for Noctiluca and Pilema octopus: that the single specimens are
driven through the whole fjord by the current from the North Sea, or are killed
by the brackish water if they enter the more closed coves; but it appears
that the diatoms are capable of forming independent floras in the water while this
is moving through the fjord, so that a diatom-flora occurs already in Nissum-
Bredning, reaches its maximum in Sallingsund, and dies away in the vicinity
of Løgstør. Organisms of so short duration of life as the diatomaceæ are there-
fore, evidently, only to a certain degree fit to follow the currents of the sea through
longer periods or through longer distances. The more uniform the natural con-
ditions in the course of such a current are, as for instance in certain great
oceanic currents, the more unchanged its diatom-flora will be sure to keep;
but any current of somewhat greater length will, as a rule, be subject to chan-
ges, changes of light among others, and the diatomaceæ are highly sensitive
to even the slightest of these changes. On the maps of the north-Atlantic
plankton, published by Professor P. T. Cleve in his fine work: »A Treatise on
the Phytoplankton 1897«, we see, for instance, that the plankton-types on the
whole follow certain sea-currents, I suppose as long as the chemico-physical
conditions of the water are the same, and I am sure that, within certain limits,
we can here conclude from uniformity in the diatom-plankton to uniformity
in the chemico-physical conditions of the water; but simply to conclude from
uniformity in the diatom-plankton of two volumes of water to a yearly repeated
current-connection between them seems to me to be unjustified. Just as fresh
waters without any connection with one another can have uniform diatom-
floras, so it is quite likely also that this can be the case with the seas. — As
some authors seem to have found it difficult to explain the occurrence of cer-
tain arctic shore-diatomaceæ in the Baltic Sea, I shall as to this question refer

12
to my observations in »Hauchs Togter«, p. 462, and to my treatise »Om de
skalbærende Molluskers Udbredningsforhold«, 1888, p. 44 seqgq., on the occur-
rence of arctic animals in the Baltic Sea. I do not see that it is more diffi-
cult to understand the occurrence of the arctic diatomaceæ «than that of
the animals. It may even be explained in various ways; it is not necessary
to presume that there are yearly currents connecting the arctic seas with the
Baltic.

To be sure, it is possible that certain diatomaceæ are fitter than others
to follow the currents, but I dare say that, as a rule, they can but with great
caution by used as »floaters«, i. e. objects thrown into the water in order to
follow the course of the current through long distances and under changing
conditions. They can shoot up and die away so suddenly that I must compare
it to the formation of a cloud which appears at every high mountain-top near
the shore when it is met by the damp air from the sea. The cloud stands still
in the air-current, certainly, but the single drops of water are constantly re-
newed, fresh ones being continually condensed on one side while others are dis-
solved into invisible mist on the other side of the cloud.) —

As soon as it had been decided that the Biological Station in 1897 should
commence investigations in more open seas, i. e. outside our narrow fjords,
I set to work to construct an apparatus which could fish plankton in the
deeper layers of the water without getting at the same time plankton from the
surface wåter mixed into it. I tried to make a closing-apparatus to Hensen's
ordinary »quantitative« plankton-net, so that the opening of the net might be
closed at any depth by a falling weight, while the bag, as usual, is sunk open
to the depth from which one wants to fish, exactly, consequently, as when it
is used in the ordinary way. I succeeded at last in making a closing-apparatus
which we could use, which closes the opening of the net with two plane and
horizontal brass plates that stand perpendicular when the net is open. I shall
put up the further description of this apparatus, as I should like to make it
more perfect in its details before I describe its construction; as it is, however,
it is certainly quite fit for use and, particularly, it eloses perfectly tight while it
is hauled up. Ås the first experiments I have made with it have really given

+) It would be interesting more closely to investigate the occurrence of the young
oyster in the Limfjord, and to follow its development during the time when it appears
in masses in the plankton. It would for instance be possible, I think, approximately to
calculate how many grown-up oysters there live in the fjord, when we counted how many
young ones they brought forth. It would certainly be much easier to undertake this inve-
stigation than Hensen's attempt at counting the plaice in the Baltic Sea,

15

results which have at least informed me of certain conditions of the plank-
ton which I have not kuown or imagined thus, I shall give these results
already now.

The first time I tried to use the new apparatus was the 5. May 1897,
on 22 fathoms of water, north of Nordre Rønner near Læsø. (See table II,
column 7.) Measurements of the salinity showed here that we had from the
surface to a depth of 5 fathoms a salinity of 2,,,—2,5, p. ct., while the water
on 10—20 fathoms was about 3,, p. ct.; it was also somewhat colder down
here, and while the current above ran northwards, it ran southwards below.
Two quite different masses of water stood thus above one another here, a
phenomenon which is rather common in the Cattegat; nay, it is almost the
rule at most places here. I must suppose that these two masses of water had
a very different plankton, and made a haul, therefore, with the closing-bag,
from 20 fathoms perpendicularly upwards to 10 fathoms, where it was closed.
Å perpendicular column of 10 fathoms of the salt water was thus fished
through, and proved to have rather a rich, brown diatom-plankton, which in
spirit immediately turned grass-green. The bag was well rinsed, and then we
made another haul from 5 fathoms to the surface. Also here was a rich dia-
tom-plankton, but it was white and had an appearance not unlike cotton.
Immediately, while on board, I felt convinced that these two masses of water
had thus quite a different plankton, and this, in a way, is also correct; but a
later investigation showed (See table II) that, after all, on the whole it is the
same species of plankton we find in the plankton above and below, and that
this particularly holds good with respect to the commonest species there:
Chætoceros boreale and Thalassiothrix Frauenfeldii; a number of rare forms are,
on the other hand, found im the deeper, salt water only. This result was a
great surprise to me; first to find the plankton of the two masses of water
quite different in colour, and then to see under the microscope that both sorts of
plankton nevertheless, on the whole, consisted of the same species. Not till
it dawned upon me that all, or at any rate nearly all, the diatomaceæ in the
plankton of the upper water were colourless and filled with water, as also
generally without any trace of cell-substance, dead consequently, while the same
species in the deeper water were strongly coloured and /iving, I got the full
understanding of the matter. Ås I have not had much to do with diatomaceæ,
I have laid the question before Mr. H. Gran, and he has embraced my views
of the matter. ”)

=) After the above had been written, I saw in the »15. Annual Report of the Fishery
Board for Scotland, 1896«, printed 1897, p. 215, that G. Murray had made a similar discov-

14

When we see that such masses of diatomaceæ, in this case Chætoceros
boreale and Thalassiothrix Frauenfeldii, are carried into the Cattegat by the
salt (c. 3,, p. ct.) under-current, it seems quite probable that these masses,
when they are killed by the lower salinity (c. 2,, p. ct.) (and perhaps by the
higher temperature), which they necessarily must meet farther southward, either
sink to the bottom or drift out again, as their specific gravity is higher or
lower than that of the water; such dead diatomaceæ are a very common phe-
nomenon, I dare say, in our seas. Column 6 in the table, May 6., 97, conse-
quently the day after the first observation, showed nearly the same conditions
at Nordre Rønner, while column 8 shows that the living plankton at Hirts-
holmene goes up to the very surface; but here the water is certainly also
more than 3 p. ct. up to the very surface. The density of the plankton was
here very considerable; more than 9 gr. were gathered from 5—0 fathoms.

Table II shows, however, that dead plankton was found also at other
places than at Læsø. Far down the Sound and in the eastern Cattegat it
occurred in May 1897, but always in water of a salinity lower than 3 p. ct.
Having pointed out, as above mentioned, the rich diatom-plankton in the salt
water and in the under-current, which comes from the north in the northern
Cattegat, I wanted very much also to find this plankton farther northward in
the Skager Rack, whence I supposed it must come. Unfortunately a fortnight
passed before this could be done; I do not suppose, however, that the lapse
of this time has had any considerable influence on the result. Columns 1—4
show the result of our plankton fishery in the Skager Rack from the very
middle of this sea (Tromlingerne in Norway, in NW >/, N, at a distance of 38
miles) towards the Skaw, at the surface as well as down on various depths;
but nowhere, except near the Skaw, on 58 fathoms of water, the density of
the plankton was found to be anything like that in the shallow northern
Cattegat. Ch. boreale and Thal. Frauenfeldu were found here, certainly, but
they were nowhere common; the peridinieæ were predominant. It was parti-
cularly the oceanic species of the diatomaceæ that occurred; of the neritie ones
only Leptocylindrus danicus was of any greater importance.

The rich plankton with Chætoceros boreale, consequently, did not come
from the north; we must therefore compare the rich growth of the diatomeceæ im

ery of dead diatomaceæ, particularly Skeletonema, in the upper water of some Scottish
Lochs, and he says with respect to this: »I believe this phenomenon, which at first puzzled
me greatly, to be due to the decline or loss of salinity of the water«. — He does not
seem, however, to have undertaken any specical measurements of the salinity; but,
speaking from my own experience, I have no doubt that he is right.

15

the salt water of the northern Cattegat to the equally local diatom-flora in the
western expansions of the Limfjord. At both places we see a current running
mainly in one certain direction, and yet its diatom-plankton is different at the
different places. In the Limfjord we might easily point to certain conditions
of the mass of water (the salinity) which are changing as we proceed east-
ward, but here in the Skager Rack and the northern Cattegat there are no
such differences of salinity to refer to, and yet the plankton changes in the
mass of water when this enters the Cattegat. That there must be, however,
certain conditions (probably the shallower water), which produce this change,
is evident; but it seems to me rather instructive to see, that the same mass of
water, on the whole of its way across the bottom of the sea, actually, is not
filed up by the same sort of plankton. F. Schritt says in his book »Das
Planzenleben der Hochsee«: »Wie es måglich ist, dass sich verschiedene Floren
ausbilden konnten bei dem fortwåhrenden Wechsel des Wassers, und wie es
ferner måglich ist, dass sich an einer Stelle eine einmal gebildete Flora
halten kann, da alle Individuen der Flora mit dem Strom naturgemåss
fortwåhrend ihren Platz åndern und in ganz andere Gegenden, die gegen-
wårtig eine ganz andere Flora besitzen, fortgetragen werden, ja, wie weit
hier uberhaupt eine Stabilitåt herrscht oder ein stetiger unregelmåssiger
oder periodischer Wechsel, das sind Fragen und Probleme, die hier bloss
angedeutet werden kånnen, deren Låsung aber der Zukunft vorbehalten
bleibt.«

In his »Analytische Plankton-Studien« he says, pp. 116—117: »Dass
die Meeresstromungen in Wirklichkeit kein vålliges Nivellierungsvermågen
besitzen, sondern dass die klimatischer Verhåltnisse des Meeres trotz der
Stromungen doch eine grosse Rolle fur die Ausbildung der Planktonmassen
spielen, das lehrt« etc. »Wir missen also annehmen, dass sich ein gewisser
Gleichgewichtszustand eingestellt hat zwischen dem veråndernden und dem
gleichmachenden Princip.«

Schiitt here expresses thoughts which are nearly identical with those that
occurred to me by my study of our coast-plankton and our coast-currents.
Unfortunately, so very little is known as yet of these things; it is certain,
however, that the habitus of the diatom-plankton often changes much in a
flowing mass of water, by little and little as the latter changes its place; and
we must be very careful therefore when we use the diatomaceæ for the pur-
pose of characterising the various currents in the sea, particularly as the
various sorts of diatom-plankton as a rule are characterised, not so much by
the perfect absence or presence of these or those species, as by the number in

16

which the specimens of the various species occur. — It does not seem to be the
diatomaceæ only which occur in the said manner in a flowing mass of water;
something like this is known also of the pelagic foraminifera, even out in the
great oceanic currents. John Murray writes thus in Natural Science, vol. XI,
July 1897, p. 21, where he discusses the distribution of the pelagic foramini-
fera: »The gradual disappearance of the tropical species, and their replace-
ment hy other species, as the colder water to the north and south of the
equatorial regions is entered, has always appeared to me rather puzzling,
especially when it is remembered that these changes take place in a continuous
oceanic current, like the Gulf Stream, flowing from the equator towards the
poles.« I take it for granted, however, that we must be able to find guide-
organisms (analogous guide-fossils) im the plankton also, which could give
us information of the paris of the globe from which they come; but
not till we know the geographical distribution of these guide-organisms,
and the conditions under which they live, we shall be able to get the
full profit out of them and recognise them as guide-organisms. I must
believe, for instance, that none of our specimens of Ctenophores properly
belong to our seas within the Skaw, hut often quite disappear from them till
the currents carry them again in great numbers into the Cattegat. Whence
these currents come I do not know, but they are scarcely identical with those
that carry Pilema octopus, another supposed guide-organism, to the west-
ern Limfjord almost every autumn; perhaps they are the same currents as
now and then carry Clione limacina to Bohuslån and the Little Belt. These
animals, the Ctenophores as well as Clione, are so large that they could
scarcely escape notice if they lived here constantly; at least it is this suppo-
sition which makes me look upon them as visitors here only, but I grant that
the whole matter is in great need of renewed investigations. Probably we
shall also among the smaller organisms, for instance among the diatomaceæ,
be able to find such guide-organisms, and perhaps for instance Rlizo-
solemia styliformis is such a one; hut it will be necessary, before it is raised
to its dignity as such, to prove that it is not »stationary« in our seas at any
time. It would be desirable to point out such organisms among the smaller
organisms, for instance among the diatomaceæ, because they are so nume-
rous that they are found nearly in every, even the smallest, sample of
plankton.

The above mentioned rich diatom-plankton with CX. boreale in the north-
ern Cattegat can, as it is seen from table II, im which the localities are
arranged from north to south, follow the bottom-current down through the

17

eastern Cattegat (the light-ship of Fladen) into the Sound at the isle of Hveen,
as far as the deep water goes. In the Cattegat it is covered by a dead plank-
ton, which however, the farther south we go, is mixed more and more with
Rhizosolenia alata, whose light colours resemble those of the dead plankton
very much. In the Sound, where the uppermost 3 fathoms have only a sali-
nity of 0,85 p. ct., not even BR. alata is found in the surface water, but only
in the middle parts (c. 2 p. ct.), while the lowest water (3,,,—3,%, p. ct.) has still
a rich Ch. boreale plankton. The uppermost 3 fathoms of water here contain,
upon the whole, scarcely anything but a few copepoda, and come certainly
directly from the Baltic Sea. The last column is plankton from Bornholm. It
contained peridimieæ and of diatomaceæ only Chæt. danicum.

The sea from Sjællands Odde (Schultz”s Grund) as far as the Great Belt
(Halskov) had very little plankton compared to the rest of the Cattegat. Is
this the rule? As I have said, the northern and the middle parts of the Catte-
gat have the greatest quantities of plankton; but we cannot conclude from this
that it is so always. The following table III from some weeks later shows,
however, nearly the same with respect to the Skager Rack. It was this
scarcity which in the autumn 1885 surprised /. Hensen so much that he sup-
posed something must be the matter with the filtering power of the nets. There
can therefore scarcely be any doubt that the Skager Rack and its deep fjords,
as a rule, have not the quantities of plankton which the Cattegat has at cer-
tain times, whether calculated by surface-units or by cubics of water; the deeper
waters of the Skager Rack contain but very little plankton. Whether the
Skager Rack in winter time has a denser plankton than the Cattegat, is not
known, but I doubt it very much.

Table II, from the month of July 1897, in the Skager Rack and the
northern Cattegat, shows that Rhizosolenia alata has now become common in
the upper water, and that Guinardia flaccida is very common in the bottom
water; as to the rest the plankton is nearly as it was in May 1897.

In order to follow the composition of the plankton in the Limfjord during
the whole year and so fill up the intervals between the 3 excursions described
above, we fished plankton the whole winter, while the Station remained at
Nykøbing on Mors, from October 1896 till April 24th, 1897, with fitting inter-
vals.. We made use of a Hensen's »quantitative« bag, and when the Station
removed from this place, the matter was left in the hands of a fisherman at
Nykøbing. He got an ordinary, small net for »qualitative« use, after it had
been proved by experiments that it caught only about "/, of Hensen's net.
With this net he has continued the plankton fishery at the same place at Ny-

AS
aa er SØ

18

købing, so that a column of water of c. 4 fathoms has been fished through,
but he has every time made 3 hauls with the net. It had been better if he
had made 4 hauls; the weight of the plankton caught after the 24th of April
1897, in table IV, could then have been compared directly to the preceding
statements of the weight, now they must be multiplied by "/, if we want
to do so.

OF course this method of using small bags for quantitative fishery is not
quite satisfactory, but it is considerably cheaper and may very well be adopted
for these preliminary investigations.

The result of these continued gatherings at Nykøbing is found in
table IV.

There is a striking diminution in the quantity of plankton from October
till November. The mean temperature in October was 10,9 C., but in No-
vember only 5,,? C. The salinity, on the other hand, was but little lower in
November than in October.

The whole winter the plankton is very scarce; it does not shoot up again
till towards spring-time, the peridinieæ later than the diatomaceæ. Gran says
of this: »The Plankton of the Limfjord is, on the whole, more like that of
the Cattegat than like that of the North Sea; it is, however, very different
from both.

From the Cattegat plankton it differs particularly by the almost complete
absence of just the commonest Cattegat forms, viz.:

Rhizosolenia alata (summer form),

Chætoceros constrictum (maximum: March—May),

= curvisetum (harvest form),

Leptocylindrus danicus (maximum: March—May).

Chætoceros debile I never saw in such huge quantities as from the Lim-
fjord; moreover it is here rather a harvest form, while in the Cattegat and
Skager Rack it has its maximum in spring.

In May and June the oceanic forms are predominating in the Limfjord
(Rlizosolenia Shrubsolii, Chætoceros boreale and decipiens), and the plankton is
quantitatively poorer; the rich neritic plankton of April has disappeared.

In July a neritic plankton, of many species, reappears. From July till
October the changes are very gradual, as from February till April.

It is very interesting to see how the neritie diatomaceæ succeed one
another. They begin in the middle of the winter with Biddulphia aurita (a
genuine winter form which is widely distributed); then comes, in February, a

new species Lauderia cystifera. It is very like the L. confervacea Cl. from

19

Greenland; but the latter is too insufficiently known to be identified with
certainty. I think it is best therefore, provisionally, to give it a new name.

Then follows Chætoceros diadema and sociale with maximum (and resting-
spores) in April; SKeletonema costatum, which seems to vegetate in great masses
till a little after midsummer; somewhat later C4. debile, which in October
forms the main mass of the plankton. CX. contortum, which in July is a cha-
racter-form, is not yet found in April in greater quantities. All these species,
which occur in the Limfjord in considerable numbers, are very widely distri-
buted, with the exception of Lauderia cystifera; most of them are found, for
instance, on the shores of Greenland and at Lofoden, where I never found the
commonest Skager Rack forms, such as Ch. constrictum, curvisetum, Schiittir, or
Leptocylindrus danicus.

OF oceanie forms a few are also found; these are very hardy, and can
live nearly everywhere, particularly Thalassiothrix Frauenfeldii and Chætoceros
boreale. They differ from the neritic forms by not forming resting-spores
under unfavourable conditions; they either die or continue to live in quite
small quantities. Single specimens of these species seem to occur nearly every-
where in the sea, as well in the open ocean as along the shores.«

It might appear from table IV as if, im May and June, unusually great
masses of water had come in from the North Sea, with North Sea plankton
in predominant quantities, which had supplanted the neritic plankton which
otherwise belongs to the Limfjord; but the salinity, which is measured by the
Meteorological Observatory at Oddesund, does not seem to indicate this. Pos-
sibly there is every year such a period at midsummer; future investigations,
however, must prove that. In order to give the most necessary data for the
consideration of this question from a hydrographic point of view, I shall state
here from »Meteorologisk Aarbog« the measurements from Oddesund in 1896
and 1897, expressed in mean numbers for the various months.

Salinity at Oddesund, in 1896. Monthly means in p. ct.

Jan.” Febr. March. April. May. June. July. August. Sept. Oct. Nov. Dec.

2 87 3,03 2,96 3,02 305 3,16 3,22 3,55 3,16 299 291 2,69
and Temperature in ?”C. (Monthly means.

15053053 ES EEN GIFT se TAS Sr VO BE NR

Salinity at Oddesund, in 1897, Monthly means in p. ct.

£
2 64 2,73 2 39 235 277 290 299 LÆR 2 85 2788

and Temperature in ?”C. (Monthly means.)
ORE DSE INGER ETT 216 SETE NS gr 3 En:

75

20

These measurements have been carried out in the surface of the water,

but where the depths are so inconsiderable as in the Limfjord there is no
very great difference in temperature and salinity above and below. We see
the considerable changes of temperature according to the season, from
0,»

18," C., while the temperature at the bottom of the deep Scandinavian
fjords is 6—8"? C. all the year round. The salinity reaches its maximum in
summer, but there is no slight difference between the two years, both with
respect to salinity and temperature. —

Ås the Limfjord is a very peculiar water, the like of which will scarcely
be found at many places in Europe, I shall give some information of it, in
order to make it easier for the foreign reader to understand the peculiarities
of this remarkable fjord. This is so 1nuch the more necessary as the foreign
literature seems to attach some importance to the understanding of the condi-
tions under which the plaice lives in the Limfjord, and, among others, the
well-known English maritime biologist E. W. L. Holt has done me the honour
of making this matter the subject of a close investigation in »Journ. Mar. Biol.
AssocreE vol VEI S ITD DES 88]

»As it is well known«, says J. Collin in his "Limfjordens marine Fauna
1884, »the part of the Limfjord which is west of Løgstør might till the year
1825 be said to consist chiefly of a complex of larger and smaller fresh-water
lakes, which were in connection with one another and had their joint outlet
into the Cattegat through the long, proportionally narrow arm of the sea be-
tween Løgstør and Hals, the water of which according to circumstances entered
with different force.«

It was in 1825 that the great irruption of the North Sea took place and
changed the salinity, fauna, and flora of the tjord, so that the old fresh-water
and brackish water fauna was driven into the narrowest creeks, and a salt-water
fauna immigrated from the North Sea: oysters, lobsters, plaice, etc.

The mouth of the fjord by the North Sea (at Thyborøn) is at the nar-
rowest place only a few hundred yards broad, and is, where it is deepest, ce.
3—4 fathoms: inside, on the »fjord-shallow«, as well as outside, on the »sea-bar«,
the passage is broader, but also much shallower, c. 8—9 feet. On account of
the »wanderings« of the sand; the depths change very much; and in order
to keep a fairway for the vessels, it is necessary indeed, every year artificially
to dig up the sand at the fjord-shallow by means of a sand pumping-ship. At
the eastern mouth, by the Cattegat, they keep (artificially also) a depth of e.
18 feet, but at several places in the narrow eastern part of the fjord, the depth

is at the deepest only 6—10 feet, The depth in the great western expansions

21
(»Bredninger«) may be said perhaps, on an average, to be 3—4 fathoms, and
only quite exceptionally, in a few holes, a depth of 11—13 fathoms, is reached.
— Though we can trace tide-currents at many places of the Limfjord — which
most frequently, however, are very irregular — they cannot be said to exercise
any perceptible influence on the height of the water, except at the very mouths,
and even here the difference between high-water and low-water is only a few
inches. — In the main course of the fjord, from the North Sea, east of Mors,
past Løgstør to the Cattegat, a distance of c. 92 miles, we find, however,
nearly always rather a considerable current in the water, running now east-
ward, now westward, most commonly, however, eastward. It seems as if this
current differs very much in the different years. It is said, for instance, in
some years to run, decidedly, much oftener eastward than westward; in other
years this difference is not so marked, though it must be said that there always
runs more water through the Limfjord eastward than westward. I think it
even very improbable that any mass of water ever runs through the Limfjord
from the Cattegat to the North Sea, as the average salinity of the year, in
1896, was 1,, p. ct. at Aalborg, 3, p. ct. at Oddesund, and 3,, p. ct. on the
western shore of Jutland.

The strong currents in the narrow sounds, in the main course of the
fjord, Thyborøn, Oddesund, Sallingsund, by Løgstør, etc., are weakened of
course, when they reach the large, remote expansions in the western part.%)
— On account of the inconsiderable depth of the fjord there is generally no
difference in the temperature and salinity at the surface and at the bottom.
When we have seen, how each of the frequent storms can put the light
materials of the bottom in motion, so that the whole mass of water gets a
yellowish colour, we understand that there is, as a rule, but one layer of water
in the expansions of the Limfjord. In quiet weather the volumes of water
which come pouring into the fjord from the rivulets, may certainly make an ex-
ception to the rule, but these exceptions are always very local and of very
short duration. —

It will be understood, what an immense difference there is between a
fjord like this with a mass of water, which is frequently renewed from bottom

£) In the above-mentioned article by Holt, thea uthor wants information of the speed
of the current in the Limfjord, especially in order to judge, whether it canhave any in-
fluence on seining, for instance by gathering the arms of the seine. I shall state, there-
fore, that in the very expansions, particularly in the large ones, the current is generally
not so strong that it has any perceptible influence on seining. His supposition, loc. cit.,
p- 82, that the seinings I have mentioned are undertaken »under practicallvy identical con-
ditions of tide, weather, temperature etc.« is therefore quite correct.

Do
(59)

to surface, and one of the Scandinavian fjords of 1—200 fathoms' depth. It is
only in the uppermost layers of the water that the latter in summer-time can
reach the same degree of heat as the Limfjord-water, and as they are always
rather deep quite near the shore, the warm volumes of water will, so to speak,
never touch the bottom of these fjords, but only dash against the shores on a
very narrow tract. The bottom of the fjord, on the other hand, is covered
with water, which all the year round has a temperature of c. 6—8? C. It is
easy to understand that the conditions of the growth of animal and vegetable
life down here are so different from what we see in the Limfjord, but why
the upper layers of water in the Scandinavian fjords have not so rich (dense)
a plankton as the Limfjord, is not so readily percived, particularly because
the same organisms are found at both places, though not in the same quanti-
ties. We might imagine that the diatomaceæ found better conditions of food
in the Limfjord-water than in the deep northern fjords, as many substances,
compounds of nitrogen for instance, no doubt are carried into the Limfjord
from the surrounding fertile land. This thought has been expressed before by
V. Hensen in. order to explain the different densities of the plankton in gene-
ral.. We might imagine also that the deep fjords actually produced as much
plankton in the surface-layers as the shallow ones, but that part of the orga-
nisms by little and little sink down through the cold layers below, while in
the shallow fjords the motion of the water compels them to keep floating
somewhat longer over the bottom, so that there are actually, at any given time,
more organisms (particularly diafomaceæ) in the mass of water. It would be
necessary then to point out such surface-forms in the deeper water of the deep
fjords, and when this has not been done, the reason might be that so few in-
vestigations with closing-nets have heen undertaken, partly also, that these
forms will occur very scantily, because they are to be distributed in such great
masses of water, and perhaps quickly sink through them, perhaps are even
dissolved in them. It is indeed strange to see, how little we find on the bot-
tom, even in the Limfjord, of the masses of diatomaceæ that have lived in its
water. We might expect to find its bottom covered with silicious shells, but
there are next to none. I must suppose that they are again dissolved in the
water, for they are neither carried out east nor west. It is possible, however,
that neither of the two said hypotheses to explain the different densities of
the plankton is correct; we must have further investigations, before it is worth
the while to discuss the question more closely. When we see the water from
the Skager Rack, with its plankton of slight density, enter the Cattegat as a
bottom current, and here immediately obtain a very dense plankton, it cer-

23

tainly seems that the interaction of the water and the bottom of the sea is alone
sufficient to produce this denser plankton, a supposition which, when we think
of the special growth and propagation of the diatomaceæ, is perhaps not quite
impossible either. —

During these plankton studies a number of questions have crowded upon
me, for the solution of which I still want the necessary information, such as:
Åre masses of fish-eggs carried from the North Sea into the Cattegat, and is
it in this way that the plaice is preserved in the Cattegat in spite of the over-
fishing? Which of our seas produces the greatest quantity of plankton per []
mile a year? Have our other fjords an independent diatom-flora like that of
the Limfjord? Has the unequal density of the plankton of the Limfjord in the
various years any perceptible influence on the sustenance of the stock of fish?
Before these and similar questious can he solved, the plankton investigations
must be carried on far more rationally, in all our seas and at all seasons, than
it has hitherto been possible for me to do.

NOE NREN EG EP ASA

Map of the Limfjord with the Stations 1—11.

.
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— Salinity, in per cent.

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++
Er

Neritic Diatoms. | | |
"ra rese ale ele Ret DL EL SERR RR | KRSESREN HaSREES KOR] KEDEDE SMERESE HEDE SR; r ER rer. ||| LØN SSR HS ARR) VANER ESR0 | BE

> balticus. Grun……. |... rr Seed er Se EN NES BE EB SR ar need RER se E 1] Fo or EOS nm - å
Sceletonema costatum. Grev. .… . EEN SEN DE UGES | EGER HESSEL, SX SES] MT SYSGEEE HØSSEEEE | BES SSER | HEEREESSED RNEE bu TE DELSE ANES BORE Men + (u ce (u + + za] IKE SES (u c ce ce ce ce |
ED De rr LSE ss Se] fr SEN SAN EET) GSR] (SIR) FOSSER Fader Re IEEE eN BESES TEEN [SEERE] PEDER 1] | Ted POBSDESE | BØRSGDER rul! | | |
Guinardia flaccida. Perag......….. ae Or ia SEERE EEN | IE Toe
— Leptocylindrus danicus. Cl. …. | .… EDER DES SEE EA DEER EEN BEEN MEETS ES SEN FE, ON] HV
Rhizosolenia setigera. Brightw.… | .…. | .… | .… r r an ED g ju + + sk |

> Stolterfotii. Perag…. | .… || .….. | + + ||

an

+ ++
+
E
+
+
+
+

+ +

Ditylum Brightwellii. West... r So HH |

Cerataulina Bergonii. Perag. NI EEGE SØGEN ore i =j 5
Eucampia Zoodiacus. Ehb. . T Xt ” SE" RE 40 NEDE ASSER FERERESEN BESAT HESEEEE ] | ESTER BERN rs TØS He 5 ss r
Biddulphia aurita. Lyngb. . SE SF æ da 7

, mobiliensis. Bail. . 5
Chætoceros Weissflogii. Shiitt……

REE TU OSSE RERER SE) RESEN BEER ESS ED FS] SHEEN ES] PEST A SEA FOSSERA LEE SED PASSE) 8 ED ONES] NS aa se SER Fr SS NERE SEE BEES
se sms OC …… …« … …… BE …..… …… …… …… T

+
+
+

eres dne 7 FO SAN ØL EREn | el | SR RREEESR |HERRRER (SEERE | fre
didymum. Ebh. ...…. USE TE + H- z
IFLG e haft re ARE] HEE SERENE) fS feet s.
breve. Schiitt…....... HR LESS
coronatum. Gran.
curvisetum. Cl. RE NESS SE San] USS USET] HESS] HIST ERE ESBERN GE BE HEE >
deles CSE: SN | SEE | FEER HENT YG ece |. cce cec c ce ce cce c T TRE ves SEE SEER |Irls ere + c 4
diadema. (Ehb.) 21 ks 3 BA LSE GA FS BLA) BEEN SEGS KRAGE ERE ISSN (EET EEESEE RS SETE" AE FRE eee ER | ostene tee BEDE 2 STE c c
leve. Schiitt EBM SEERE] lars HEER URE Ser] URESE STAN [LSE SENGE HRESEa PN) [EROS SAS | SØE L EEN HE BRAE | SE DE HENØRSE ad HAr Here ør …s
crinitum. Schiitt..….
externum. Gran. .,..
(=f eds ban ER 0) FT KE NESRGE
simile. Cl...
subtile. Cl. ..…
cinctum. Gran... Se
Bociale GIS Sene
scolopendra. Cl
2 constrictum, Gran. ..
Åsterionella spathulifera. Cl.
Nitzschia seriata. Cl. 11"
[Halosphæra viridig. Schmitz,).…

FE
"+

+
+=
+

+
ifl

ie

+
mm —+-
+
ET

Era

Ar never RR

cs
CT
mere

é Ny ig |
eN ERR
—= Elg

HERTU
J 0—5. —5. |18-100.| 0—5. "0—5. |5—115.110-190. EET 0—7.
Br

me: t. 8 g—

ge. 210 Fathoms.

wW. a
ec. 130 Fathoms.
22. | 22. May 1891 1897.

Cape Skagen in
SEbyS.34 Miles.
130 Fathoms.

Pe

[he Light-ship okk "AnnottTiett i
Fladen in NW by N.||in SW Y, W.
4 Miles. 7 Miles.
30 Fathoms 23 Fathoms.

eridineæ.

Ce ratium tripos…....44.4044444…
EH » v. longipes.....

HH >». v. Bucephalos..

b >» »… vv. macroceros ..

BSL
=

+e

> furca

Peridinium divergens ...…. bg + r

Dinophysis BOEDE SEERE ar
Diplopsalis lenticulata .........

ceanic Diatoms.

(he

(udnodlsous oculus iridis

rTadiatus..…...….…

concinnus .......

RH-olp lenin styliformis,.......
> semispina .....….…

> Fnr re ER er

> Shrubsolii ....…....

Dactyliosolen mediterraneus ....

Chætoceros atlanticum

H<:

boreale. .

danicum

eriophilum ...
decipiens ..

jalassiotbrix Frauenfeld

> longissima ,.....

eritic Diatoms.

balassiosira Nordenschidldii .…

, [raa ra te > ARE RSS
Kesctnodiscus polycordus.. ....
excentricus,.....

SHE niyeLus undulatus
Lauderia annulata
Guinardia flaccida … …
Leptocylindrus danicus ,
Cerataulina Bergonii ….
bizosolenia Stolterfothii
i setigera
bucampia Zoodiacus
itylum Brightwellii.
Biddulphia aurita ....
i mobiliensis.
Chætoceros contortum

, Brave se

curvisetum |,
debile…—…………

>
>
2 scolopendra
EJ
tj

Nilzschia seriata

erinitum
didymum
Wiilei …

itu

ei
DE Cc
San en
År: dd
fig bes
… 2 al

E.

SSER

ocs+

Fri

liv. |dead.| liv. | liv. dead. | liv. liv. | dead. im dead. | liv. dead. | liv.
r + r eee
+ r r r SØGE ”. G + ik
E
Ed iz + ' c
c + Ce
(u ce r
r
Fl+)
vr
E
X
ES
r c
nl
||
||
r + hes
w SE
S;
c
T

-

ms el Ass LA

SÅ

Table III.

Locality and Depth.

NNE of Cape Skagen.
95 Fathoms.

Paternoster in NE.
8 Miles.
55 Fathoms.

The Light-ship of|

Cape Skagen in

SSE. 3 Miles.
49 Fathoms.

Nordre Røn-
nerinS",, W.
10 Miles.
20 Fathoms.

Nordre Røn-
ner in S.
20 Fathoms.

Date.

13. July, 1897.

1. July, 1897.

1. July, 1897.

3. July, 1897.

9. July, 1897.

Fathoms fished through.

0—10.

15-30.

40—90.

0—10./18—29./30—50.

0—10. | 15—45.

0-7:

11 IS)

0—5. |10—19.

Salinity, in per cent.

3,93—

>

388"

8, g—

148"

8517

751"

gr 8 gg 30

2 36: 740"

Quantity, in Gram.

eridineæ.

(Er UNITEITI POSTE En afarter sner,
> 3 nv. longipes.
> »… v. Bucephalos..
> »… vv. MmMaCcroceros ..

. Peridinium divergens.... É FE Så
IDmopbysis ac eee eee
Diplopsalis lenticulata .........

ceanic Diatoms.

Coscinodiscus oculus iridis. Ehb.
> radiatus. Ehb. ...
>» concinnus. Sm. ..
Rhizosolenia styliformis. Btw...
> semispina. Hensen.
>» alata Bwin
> Shrubsolii. Cl. ….
Dactyliosolen mediterraneus ....
Chætoceros atlanticum. Cl1......
> boreale. Bail. ......
> damen Ol SE
> criophilum. Castr….
> decipiens. Cl...
Thalassiothrix Frauenfeldii. Grun.
> longissima. Cl. ...

eritic Diatoms.

Thalassiosira Nordenschidldii. Cl.
> Øramdan Clerisie
Coscinodiscus polycordus. Gran.
> excentricus. Ehb.
Actinoptychus undulatus. Ehb. .
Lauderia annulata. Cl. …Å.…......
Guinardia flaccida. Perag.......
Leptocylindrus danicus. Cl. ....
Cerataulina Bergonii. Perag.....
Rhizosolenia Stolterfothii. Perag.
> setigera. Btw......
Eucampia Zoodiacus. Ehb......
Ditylum Brightwellii. West. ....
iddulphia aurita. Lyngb.......
» mobiliensis. Bail. ...
Chætoceros contortum. Schiitt. .
» breve. Schitt. .....
» constrictum. Gran. .
> curvisetum. Cl. ....
» deler CE Ser
> scolopendra. Cl. ...
> crinitum. Schitt… .
> didymum. Ehb.....
» Wille: Gran 14555%
Nitzschia seriata. Cl... Re

i.

o+ +e

"+:

”2"

Bog 349—

337" 750"

Ps

378"

3 ,og—

331"

339. 0,

5"

(«)
GG
==

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E

s+e:

1,73: 0,6:

em:

om

oms —
<ugg 3 103
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792" 138"

BI 15

cc

sg

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kJ firerne

i Peridinium divergens ….

" Oceanic Diatoms.

"Coscinodiscus radiatus, Ehr.….….
Rhizosolenia styliformis. Brightw..
2 semispina. MHensen.
> Shrubsolii.C1.…....…..
calcar avis. Schultze.
CREtocEree boreale. Bail. NE
> eriophilum. Castr..
2» ,… danicum. Cl. . Es
decipiens. Cl...

Thalassiothrix Frauenfeldii. Grun.

Neritic Diatoms.

Skeletonema costatum. Grev..
Thalassiosira Nordenschidldii. Cl.
Lauderia cystifera. n. sp....... i
Guinardia flaccida. Perag. .......
Rhizosolenia setigera. Brightw. ..
Ditylum Brighiwellii. West. ..…
Lithodesmium undulatum. Ehr.….
Eucampia zoodiacus. Ehb. ..…...
Biddulphia aurita. Lyngb….....
7 mobiliensis. Bail. .….

contortum. Schiitt. ..
didymum. Ebr. ..…….
laciniosum. Schiitt…
breve. "Schutt.
[ST INSEE 6] FEER ES
coronatum. Gran. ...
Bchlttill CLAIRE
LET ork FE. CJ RR RE
diadema. (Ehr.) Gran.
scolopendra. Cl. ,.…
sociale. Laudr. ....
Wighami. Brightw….

> gracile. Schiitt.
Asterionella spathulifera. Cl. .…
Achnanthes taeniata. Gran. …..

va sEvss3vuv

The temperature of the water, in
KG Fat Oddemna series rereEe

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nl

r T +- r E + +
ne ie NOR r r
r i + e (g T r RR Vee
BONE æ: + c (uu ece | cce | cce | ccc

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£ The great weight is here owing to larvæ of bivalves and snails.

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