FISHERIES AND MARINE SERVICE
Translation Series No.
4545
Investigations concerning the bond between indigenous
pelagic crustaceans and their biotope
by 0. Siebeck
Untersuchungen zur Biotopbindung einheimischer
Original title:
Pelagial-Crustaceen
From:
Verh. Ges. Okologie p. 11-24, 1973
Department of Fisheries and Environment
Fisheries and Marine Service
Canada Centre for Inland Waters
Burlington, Ont.
1979
22
pages typescript
4
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TITLE IN ENGLISH
TITRE ANGLAIS
Investigations concerning the bond between indigenous
pelagic crulitaceans and their biotope
TITLE IN FOREIGN LANGUAGE (TRANSLITERATE FOREIGN CHARACTERS)
TITRE EN LANGUE ÉTRANGÈRE (TRANSCRIRE EN CARACTÈRE3 ROMAINS)
Untersuchungen zur Biotopbindung einheimischer
Pelagial-Crustaceen
1
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Verhandlungen der Gesellschaft für Mcologie
REFERENCE IN ENGLISH — RÉFÉRENCE EN ANGLAIS
Transactions of the Ecological Society
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0.Siebeck:
"Untersuchungen zur Biotopbindung einheimischer Pelagial-Crustaceen;" Sonderdruck. Verhandlungen der Gesellschaft für Okologie,
CIE
'pp.
11 - 24; Saarbrücken. 1973.
1
(11)
O.
Siebeck*) 1,2
INVESTIGATIONS CONCERNING THE BOND BETWEEN
INDIGENOUS PELAGIC CRUSTACEANS AND THEIR
BIOTOPE
Abstract
An organism's connection to the biotope is the result of adaptation of its vital requirements to
the given environmental situation. The adaptation arises during its course of evolution. ln
immotile floating organisms and in sessile forms, the analysis of the connection to the biotope
lies exclusively within the field of metabolic physiology. In motile organisms behavioral studies also play an important role in this analysis. The report submitted is limited to these studies.
Three typical behavioral patterns of the pelagic crustaceans are discussed. 1. Diurnal vertical
migration, 2. avoidance of the shore, 3. behavior in the current. In the discussion covering the
significance of these behavioral patterns for the biotope connection the vertical migration is
valued as an adaptation to the heterogenous spacial distribution of the food. In avoidance of
the shore, not only are unfavorable vital requirements of the litoral zone eluded, but the
danger of drifting into the outflow of the lake is reduced.
-• --
The linking of the various species of organisas with different
biotopes is the result of the evolutionary adaptation of their vital
requirements to the given environmental situation.
Strictly speaking,
this would imply that it is possible from the properties of a biotope to
deduce some of the vital requirements of its inhabitants and vice versa.
1
*) Abbreviated version of the lecture read at the Convention of the
Gesellschaft für Ôkologie [Ecological Society] on 28 September, 1973.
2
15 Dedicated to Dr. Franz BERGER, Biological Station of the Austrian
Academy of Sciences, Lunz, on his 70th birthday
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2
At the outset an analysis of this state of affairs appears quite out of the
question, considering that the environment of an organism is made up of
a multitude of abiotic and - most of the time particularly complex biotic factors.
Nonetheless, an attempt at carrying out such an analysis
is not hopeless because the various factors are not equally significant.
Thus at least those environmental factors which are of outstanding
importance and the functional and structural characteristics 'attuned'
to them can be recognized.
I.
A general comparison between the pelagic zone and the benthic zone as
well as its inhabitants
By comparing the various biotopes of a lake from the point of view
of the demands they impose upon their inhabitants, one finds two zones
differing markedly from one another by one property: the benthic zone is
the biotope that provides its inhabitants with a solid substratum, where
they may either remain permanently in one place, move about, or at least
fix themselves from time to time. This possibility is absent in the
pelagic zone.
As a rule the inhabitants of the latter never have any
contact with a solid substratum. This is a unique situation, for which,
incidentally, no parallel exists anywhere in the terrestrial biotope.
A comparison between the inhabitants of these two biotopes demonstrates
the ecological importance of the described difference: typical inhabitants (12)
of the
insofar
shore area, of the slope of the basin and of the lake bottom,
as they are able to move about by swimming, do not persevere to
any great extent in this activity. They often develop special clinging
mechanisms.
Many representatives of this zone are altogether incapable of
any noteworthy locomotion without a solid substratum.-
3
The typical inhabitants of the pelagic zone had to make themselves
independent of the substratum.
Essentially, they have accomplished this in
three different ways: by largely or even completely adapting their
specific gravity to the surrounding medium; by increasing their form drag
(decrease in their sinking velocity); and finally by developing great
swimming endurance.
At the organizational level of the invertebrates, the ability to
float in suspension and a high form drag are combined with a lack of or
only low motility.
The endurant swimmers have a relatively low form drag
and their specific gravity is higher than that of the surrounding water.
The tendency to sink must be constantly countered by swimming in the opposite
direction, a habit that is observed, for instance, in all the pelagic
crustaceans.
Consequently, the ecological significance of the emphasized difference
between the benthic and the pelagic areas results very conspicuously from
a comparison of the locomotive properties of their inhabitants. Further
characteristics of the benthic and the pelagic regions are derived from,
among other things, the observation that the inhabitants are not
uniformly distributed in either biotope.
Indeed, the spatial differences
in the distribution of organisms down the gradient of environmental factors
are an important starting point for an ecophysiological analysis of the
bond with the biotope.
In the case of immotile floating organisms and of sessile forma
this analysis is restricted exclusively to the field of metabolic
physiology.
In the case of other, motile, organisms, however, behavioural
study also plays an important role. By being capable of seeking out favourable
regions and of avoiding
or leaving others, these animals by their behaviour
4
indicate environmental properties which are of indirect or direct
significance to themselves.
The remarks that now follow will be confined to
this aspect.
II.
Three typical behavioural patterns of pelagic crustaceans.
Three typical behavioural patterns of pelagic crustaceans - the
methods of the investigations are shown in F i g. 1 - are of particular
significance for the binding of these organisms to the pelagic zone:
(1) the behaviour under the influence of the ditulaal/light/dark change;
(2) their behaviour near the shore and (3) their behaviour in the area of
the
lake
(1)
outflow.
The behaviour under the influence of the diurnal liet/dark chanze
(diurnal vertical migration).
It has been proved for numerous crustaceous species of the pelagic
plankton that the daily course of radiation intensity is of extraordinary
significance for their vertical distribution. In all these cases a daily
cycle of vertical migration is observed that leads to a considerable
displacement of the population which will be described on the basis of the
distribution patterns of Daphnia longispina in the Lunz
conseutiv
Untersee (SIEBECK 1960) and of the behavioural patterns, as observed in the
laboratory, in Daphnia magna (HARRIS & WOLFE 1955); it is very likely that
this behaviour is equally valid for Daphnia longispina (F i g. 2).
(1)
During early morning twilight Daphnia longispina migrates in
the direction of the lake surface. In this area the size of the catch
increases.
In the laboratory one observes under these conditions that
Daphnia magna invariably swims along a vertical path, independent of the
spatial distribution of light intensity. Since eyeless animals exhibit
5
1 00 '
Daily course of
togonang der
KLX
arteuchtungsstOrke
60
light intensity
20
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is
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12
à 2,2 ut
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vIertikotverteiung
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Vertical distribution
4
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(
Behaviour
Verhifilten
î
of
von
Dophnio magna
F i g. 2. Progress of the diurnal population movements through vertical
migration by Daphnia longispina on a day of cloudless skies in the Lunz
Untersee.
The different distribution patterns are matched with similarly shaded
representations of the behavioural patterns of Daphnia magna, as described
by'HARRIS & WOLFE 1955.
Obliquely hatched: upward migration in early morning dusk;
coarse
dots: downward migration;
white: behaviour during adapted state at daytime depth;
horizontally hatched: upward migration;
fine dots: 'midnight sinking;'
a - active component,
p - passive component of motion (sinkilig down).
...... ■■■■■■■■■■■■
•
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1.
1 1i i
Depth
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F i g. 1. Methods of investigation for the analysis of various behavioural
patterns in pelagic crustaceans.
A.
Catching device for studying the daily cycle of vertical migration.
(a): boat with mounted pump (P); tube with water meter (W) and trapping
net (N). (b): drift body for checking horizontal currents.
(c): buoy with mechanism for recording radiation (S) and several resistance
thermometers (T) to check internal seiches that might simulate active
population movements. (d): representation of catch as a function of the
depth at which the animals were taken.
B.
Plexiglas arena for studying the'avoidance of the shore behaviour.'
(a) top view of the arena; before the experiment the test animals are
collected in the connecting pipe (S); thereafter (S) is removed and the
animals migrate to the periphery. (b): top view of the arena after
the chambers have been shut by the ring (R). (c): positioning the arena
(A) in the littoral zone. (d) representation of the distribution of the
animals to determine the preferred migratory orientation.
C. Circular channel for studying the behaviour of pelagic crustaceans in water
currents. (a): atop the device is a homogeneously lighted hemisphere of
Plexiglas
one half of which has been blackened (to simulate the superelevation of the horizon). (b): top view of the installation.
analogous behaviour, it is certain that during this phase the compound
eye does not participate in the guidance (HARRIS & MASON 1956).
(2) With increasing daylight the population shifts towards the
deeper strata. In the experiments with Daphnia magna this downward
migration is preceded by a phototactic reaction: eye positions and
migratory orientation depend henceforth on the spatial light-intensity
distribution.
It is particularly notable that the downward migration is
completed before the end of the increase in light intensity (during
summer conditions and under a cloudless sky, Éhis stage is reached in the
Lunz Untersee ,--, 2 h before solar culmination).
(3) With decreasing daylight - not, however, directly subsequent
to the solar culmination - the animals resume their migration towards the
lake surface.
During this migratory phase the swimming course of Daphnia
magna continues to be dependent on the spatial light distribution: the
animais move in the direction of maximum light intensity.
(4) At night the numbers of individuals at the water surface decrease
again. Daphnia magna sinks - presumably with a negatively geotactic
orientation - due to the slowing down of its swimming activity, until, in
the early morning twilight, it is reactivated through the limited light
intensity (photokinetic effect) and starts its upward migration anew.
But according to HARRIS (1963), this upward migration does not depend on
light intensity, and hence it is supposed to be endogenously controlled.
The course of the diurnal vertical migration, as represented by the
consecutive vertical dispersion patterns, holds essentially true *) 1 for
1
*) There is no reason, in the context of the subject under discussion here,
to enlarge upon the many divergences in the course of the diurnal vertical
migration. Interested readers will find such details compiled in the
publications of CUSHING (1950) and BAINBRIDGE (1961). Nonetheless, a few of
the findings reported there must be regarded as uncertain, because of the
inadequate research methods (e.g., no monitoring of internal waves, no radiation
recordings, frequently only single observations).
The works of HARRIS & WOLFE (1955 and RINGELBERG (1964) deal with the
physiological bases of the vertical migration.
8
so many planktonic organisms of lakes and the sea that one can no longer
doubt its significance for life within the pelagic zone, despite the fact
that, up to now, only conjectures have been advanced on the specific
effect of the vertical migration (cf., for example, McLAREN 1963). Here,
we will only discuss the question whether the diurnal vertical migration
can be regarded as a 'response' to a particular property of the pelagic
zone and thus represents an essential behavioural element with regard to the
animals' bond with the biotope. The hypothesis put forward by HARDY (1938,
1956) provides the foundation for the following considerations that proceed
from two important facts:
(1).
The location of the maximum distribution in the course of the
downward migration depends on the dynamics (change in the radiation intensity
per unit time, from the start to the end of the downward migration, measured
in each case at the level of the animals migrating towards the depth) and
on the spectral energy distribution of the radiation in the water (cf.
SIEBECK 1960).
(2).
The vital conditions, such as food supply, oxygen content,
temperature, etc., are more favourable in a higher water layer coinciding
essentially with the trophic zone than in the subjacent water layer. But
even within the life-supporting aquatic zone the food supply (for instance,
phytoplankton) is not uniformly distributed..
It is easy to test experimentally that the pelagic crustaceans
respond to UV irradiation with a flight reaction. Their behaviour in
correspondingly unambiguous at a high CO2 content (UBRIG 1952), which, in
natural water bodies, is always linked with a relatively low 02 content:
under these conditions they react by migrating towards maximum light, but
not only during decreasing light intensity. A sharp lower termination :r
(16)
10
where the food is heterogeneously distributed, migration will certainly be
of advantage, even if it cannot be stopped within regions of favourable
nutritive conditions.
The significance of the vertical migration gains
more weight, when one takes the horizontal currents into account; at the
time of thermal stratification, they are characteristic of every lake. Due
to the vertical density differences in this situation, the water column of
a lake is constituted of several autonomous water bodies lying one atop the
other and having currents with different orientations and velocities (cf.
SIEBECK 1968, p. 9). When organisms migrate through these currents they
simultaneously drift in various directions determined by different bodies
of water. In this manner the planktonic crustaceans cover distances they
could never attain through active locomotion alone.
Summarizing, the situation is as follows: within their biotope
the inhabitants of the pelagic zone are faced with the situation of a
heterogeneous distribution of the food supply, brought about by various
causes, but also through the zooplankton itself (for instance, when an area
just populated by a swarm of crustaceans, has been 'eaten clean'). Under
these circumstances a change of locality is of advantage. Since pelagic
crustaceans are not in a position to locate and steer toward areas where
beneficial food conditions prevail, they have to strive for a solution that
renders an accidental discovery more probable. An area devoid of nourishment
can be abandoned, for example, through a horizontal migration. To be
successful the migratory direction must be maintained over long distances.
But this is impossible due to the lack of stable reference points. It is
not possible to use the horizontal currents to drift into other bodies of
water; only an upward or downward migration makes it possible to change from one
water mass to another with differing properties and thus - by exploiting the
11
horizontal drift - to attain a special dispersal effect in space.
The diurnal character of the vertical migration is not significant
in this context. The fact that it is observed among the various representatives
of pelagic inhabitants might mean that the adaptation of the triggering and
control mechanism (for the required frequent change of locality) to the
diurnal fluctuation in light intensity has proved the best solution.
Looked
at in this manner, the diurnal vertical migration of the pelagic crustaceans
(along with many other representatives of the pelagic zone) is a behaviour
of great significance for the bond between these animals and the pelagic zone.
The hypothetical correlation proposed is in no way invalidated by
the observation that underneath a layer of snow and ice on a frozen lake,
or under the effect of the midnight sun, no vertical migration takes place,
and yet the population still does not die out.
Under these conditions,
the pronounced thermal stratification is lacking, and this means that the
vertical exchange processes and with them the intermixing of food particles
can take place almost unhindered.
(2) The behaviour of the
Eelaec crustaceans near the shore
The spatial distribution of the pelagic crustaceans demonstrates
that their environment is limited not only upward and downward, but also still within the area of free water - in the direction of the littoral. For
the reasons explained at the beginning, it is easy to understand that
typical inhabitants of the littoral are absent in the pelagic zone. The
opposite case, however, is not immediately comprehensible. Why are typical
inhabitants of the pelagic zone not distributed as far as the shore margin?
Are they lacking there because, after having drifted into this zone, they are
always quickly consumed (by shoals of young fish, etc.)?
Are they capable
12
of finding their way back into the pelagic zone? Or could it be that they
inevitably keep away from the shore when, in the morning, they migrate
to greater depths along the sloping bottom?
(cf.
SIEBECK 1964).
With the aid of the Plexiglas arena, illustrated in F i g. 1, it
can be shown that the shore avoidance observed in the pelagic crustaceans
is indeed the result of a typical behaviour:
when planktonic crustaceans
are placed into the Plexiglas arena positioned in the shallow shore area,
they are found very shortly thereafter, given sufficient light intensity, on
the side of the arena directed towards the pelagic zone (SIEBECK 1968).
The preferred direction of this horizontal migration can be
determined more precisely if care is taken that the distribution of the
crustaceans can be ascertained as soon as they have reached the periphery.
In the illustrated installation this is achieved by radial chambers which
are open towards the interior during the experiment, and then all shut
simultaneously at the end of the test. The preferred orientation is
indicated by the position of the chanber containing the maximum of
animals.
Experimentb on different sections of the shore of a lake show
that given diffuse radiation the migratory direction is essentially
dependent on the locality, and its course is in every case towards the
pelagic zone. The same holds true under solar radiation, even though the
migratory orientation is now more or less deflected towards solar azimuth
(SIEBECK 1968, p. 77 ff.).
At first these results demonstrate merely that the spatial pattern
of light intensity is essential for the choice of the migratory direction.
Simultaneously, however, it becomes clear that the pattern of light
intensity, which can be very different at different sections of shore, must
13
contain a property that is characteristic and fundamentally similar for
the choice of the migratory orientation, since, in spite of all differences,
the animals will always migrate towards the pelagic zone. This important
property is discovered if, in the same locality, the pattern of light intensity
is progressively modified in consecutive experiments. It is found that a
darkening of the pattern of light intensity outside the area of the critical
angle (> 48.6 0 ) is unimportant for selecting the migratory direction
(F i g. 3, B + C). But as soon as the pattern of light intensity is
partially darkened within the critical angle ( 4 48.6° ), other migratory
orientations are preferred (F i g. 3, D).
The essential criterion for the choice of migratory orientation
under natural conditions is easy to discover: it is a section with
relatively low values of light intensity, the 'dark field,' brought about
by the low intensity of reflected radiation that emanates from inshore
objects above the water surface, such as, for instance, reed belts, the
slope of the shore, trees, forest and, ultimately, mountains in the
background.
All of these objects projecting above the water surface are
jointly designated as superelevation of the horizon.
Consequently, the inshore superelevation of the horizon causes
the 'dark field' within the area enclosed by the critical angle.
When this
'dark field' is extended by, for instance, the construction of an
artificial superelevation
of the horizon and modified by variations in its
position, the migratory orientation of the pelagic crustaceans can be
manipulated (F i g. 3 D).
It is not intended to enlarge here on the analysis of the orientation
preceding the observed horizontal migration in the direction of the pelagic
zone (cf. SIEBECK 1968, p. 83 ff.). It is sufficient for the considerations
14
IS,
A
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0,
F i g. 3. Experiments in the littoral for analysing the 'shore avoidance.'
Four consecutive experiments (A - D), carried out at the same locality, are
represented. Lateral view al and top view a 2 of the installation. Condition
of the Plexiglas arena without (A) and with various auxiliary arrangements
(B - D). B: the arena is surrounded by a black plate, due to which only the
area of lateral light (s) is darkened. C: by means of a black base the
area of bottom light' (c) is also darkened. D: additionally, a
superelevation of the horizon has been constructed; now the dark field (d)
within the area of the critical angle, which had remained unchanged in
A - C, has been enlarged. Only subsequent to this modification do the
pelagic crustaceans select a new migratory direction (arrows!). The pattern
of light intensity is represented only symbolically by shading the fields in
the circular areas. To comprehend this one should imagine a sphere(arranged
underneath the water surface) around the central point of the arena, upon
which the pattern of light intensity of the surrounding area is projected
(measuring element with 20 ° aperture
using a coarse grid
sphere
is
broken
down into an upper (b) and a lower (c)
).
The
angle
hemisphere. The surface projection of the upper hemisphete contains the
zenith with the critical angle area (thickly drawn circle) and the
adjacent "area of lateral light" (s). The lower hemisphere (a) contains
exclusively the area of lower light (from SIEBECK 1969, modified).
deelt with here to keep in mind the folipeng fat (f g. i ; the
euilerelevet 'ion oi the horizon crea.tee a !4,t1c “el.cplp he 4nebove region,
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17
(3)
The behaviour in the resion of
the outflow from the lake_
As was already mentioned, the planktonic organisms in the pelagic
zone are constantly seized by currents, especially horizontal currents,
and drift over great distances.
Since there are no stable optical
reference points in the pelagic zone, a compensation of the drift is impossible,
unless the currents are accelerated: since the planktonic crustacean differs
in its mass inertia from the surrounding medium, a relative motion between
the two would occur in this case, which could lead to a mechanical
stimulation, if adequate receptors are present. Through his experiments,
however, SCHROEDER (1967) recorded findings which can be interpreted in this
manner only in the case of Cyclops abyssorum. According to my own
investigations, Daphnia longispina and Eudiaptomus gracilis are not capable of (21:
Compensating for a current if no optical reference points are available
(cf. also STAVN 1970).
If Daphnia longispina is placed into a circular
current channel (F i g. 1), near Which a dark superelevation of the horizon
has been constructed, then, at a velocity of the current that can only just
be compensated for by the animal (SIEBECK et al. 1971), the following
situation is observed:
in one particular section of the circular channel compensatio
of the current is much more readily achieved than in other sections.
What distinguishes this section from all the other ones?
An examination
reveals that, here, the plane of symmetry of the superelevated horizon
coincides with the orientation of the current. Hence the interpretation
of the experimental result is simple: in the presence of the spatial light
intensity pattern characteristic of nearness to shore, the typical
'shore avoidance behaviour' is triggered.
The position of the superelevated
horizon determines the migratory direction in all areas of the circular
18
F i g. 5. Behaviour of Daphnia longispina in flowing water. At the
centre of the illustration the experimental installation is presented in
top view (cf. F i g. 1, C). During the experiment, within the fields of
the circular channel marked by dots, the orientation of 100 daphnids was
determined as they drifted through. The result of the distribution is
recorded in the respective circular diagrams. It can be seen that all of
the distribution patterns are alike, which means that the preferred orientation
depends solely on the position of the superelevated horizon. In field
c the orientation is precisely contrary to the direction of the current.
Here, the latter is preferentially compensated for.
channel (F i g. 5). With reference to the direction of the current this
means that there are only two places in the circular channel, at which
the migratory direction and that of the current coincide, and only at one
of these two places is the 'shore avoidance' precisely contrary to the
direction of the current. Therefore, the prerequisites are ideal here for
19
■
a compensation of the current.
flow direction
At the spot where migratory direction and
an angle of 90 0 , the drifting is fully effective.
It is striking that daphnids, which react only very lazily in
stagnant water to the influence of the superelevated horizon, are activated
when they drift towards such a superelevation of the horizon. This means
that the enlargement of the dark field with time is a particularly effective
triggering mechanism for the 'shore avoidance behaviour.'
The ecological significance of this behaviour lies in the fact that
it is suited to prevent the animals drifting into the outflow of the lake.
Investigations carried out thus far in different lakes (REGNAUER, in
preparation), have clearly confirmed this: at night great quantities of crustaceans
end up in the outflow; during the day, the reduced numbers of animals
moving towards the outflow demonstratethat many of them are capable of
preventing such a drift (F i g. 6). The success of this behaviour, which
was directly experimentally observed, namely, the ability to remain in the
lake, presupposes that the influence of the superelevated horizon becomes
effective in the gradient of the flowing water at a point where the current
velocity can still be compensated. It is, to be sure, very doubtful
whether this condition will also be found in large lakes, with a low
superelevated horizon and a strong outflow. It is quite certain in
any case that the pelagic crustaceans remain confined to their biotope in
the free-water zone by the shore avoidance behaviour described above.
This behaviour thus not only prevents their populating the littoral zone,
but-given the necessary conditions mentioned above - it also stops them
drifting into the outflow of the lake, which would mean sure death for
inhabitants of the pelagic zone.
(23)
20
F i g. 6. Horizontal distribution of Bosmina longirostris in Lake Bansee
(Chiemgau), according to studies by REGNAUER (in preparation).
A: courses of currents in the Bansee, with catching stations I - IV
indicated,all of which are within the water flowing towards the outflow.
B: lake profile in the outflow area, with catching stations I - IV. C:
results of the catches carried out during the day (cloud cover 10/10,
animals distributed right up to the water surface), and D: results of
catches made during the night. (Per station, 10 x 5 1 were pumped at a
depth of 0.5 m). E: velocity gradient in the area of the catching
stations.
21
LITERATURE )
•
BAINBRIDGE, R. (1961): Migrations, In: The l'hysiology of Crustacea. 2: 431-463.
cd. T.II. WATERIANN.
CUSIIING,
(19510: The vertival migration of planktonic cruataeca. llinl.Rev. 261
158-192.
FRAENKEL, G.S. & GUNN, D.L. (1961): The Orientation of Animals. Dover Publications,
Inc., New York.
11A ROY, A.C. (1938): Chang end choice: a study in pelagic ecology, In: "Evolution"
(G.R. DE BEER. cd.). Clarendon
Oxford. 139-159.
IIARDY, A.C. (1956). The open Sea, ha Natural Ilistory: The World of Plankton, Collins,
London.
11A1(1t1S, I.R. & WOLFE, 11.K, (1955): A laboratory study of vertical migration. Prot. Roy.
Suc.I.ond.Ser.li. 144: 329 -354.
11ARRIS, I.E. (St WOLFE, U.K. (1956): Vertical migration in eyeless Ltipbroid. Proc.Roy.Soc.
Lond.tirril. 145 280 -290.
IIAlt RIS, I.E. C I Vo31 l'he rade of endeogennus rhythms in vertical migration.1,Mar.Ifid.Ass.
•
UK. 43; 153-166.
MeLAREN, I.A. (1963): Effeet• of temperature on growth of Zooplankton and the adaptive
value of vertical migration. I 1.e•h.lit•%.1t.1 , Canada. 20: 685-727.
•
RINGE1.111: let • I. (19(i4): 'Ile positively !Minot actic reaction of Daphnia magsta. Straus: a eon2: 319-406.
tribution to the understanding of diurnal vertical migration. Nerb.I.Sra
1 .SCI I RODER, R. (1967): Verhalten von Cyclopi abpsorion in der Strhmung. Arcbilydrob./ • r•
Suppl. 33: 84-91.
2 SIEBECK, 0. (1960): Untersuchungen übcr die Vertikalwanderung planktischer Crustaeeen
untcr BerlIeksichtigung der Strahlungsverhaltnisse. Int.Reseme gesilydrobiol. 451 381454.
3 SIEBECK, 0. (1964): hi die "Uferflucht" planktischer Crustaceen eine Folge der Vertikalwan• •
derung? Arckilydrobiol. 60(4): 419-427.
•
4 SIEBECK, 0. (1968): "Uferflucht" und optische Orientierung pelagiseher Crustaceen.
Arcb.11ydrubtol./Suppl. 35(1): 1-118.
SWItECK. O. (1969): Spatial orientation of planktonic crustaceans. I.
The swinuning belie
vi lllll in a hinirinit al plane. l'eab.Interria.Vereirt twitted. 17: 811 847.
5 sIE1IEcK.1). & FAInvicK. G. (1 9 71): St riimungsvmserimente mit dem Planktonkrchs
l'apbma lmixmpitid by.shrbi. (: arinthia Il . Smoderbelt 3!; 159-174.
Si .% ■, N,11.1c ,1970): The Application of the Dorsal light Wail .
for Orientation in Water
eurrents hy thiphrtia onagna Straus. Z.vel'hysinl. 70: 349-362.
6 mum:. IL (1952): Orr Einfluss von Sauerstotef und Kuldendioxyd
loathe taktischen ltewcgungea; einiger Wassert iere.
vgi.l'hysiol. 34: 479-507.
Address of the author: Professor Dr. O. SIEBECK
Zoological Institute of the University
Luisenstrasse 14
D - 8000 München 2
German Federal Republic
[Translated Titles]
•
1.
Behaviour of Cyclops'abyssorum in water currents.
2. Investigations concerning the vertical migration of planktonic
crustaceans taking the radiation conditions into consideration.
3. Is the 'shore avoidance' of planktonic crustaceans a consequence
of the vertical migration?
22
4.
'Shore avoidance' and optical orientation of pelagic
crustaceans.
5. Experiments in water currents with the planktonic crustacean
Daphnia longispina hyalina.
6. The influence of oxygen and carbon dioxide on the tactic
movements of some aquatic animals.