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I Int. Revue ges. Hydrobiol. I 78 I 1993 1 1 I 1-19
JUTTA GUNMER’ and ULRICH LIEDER~
‘Bellmannstr. 33, D-W-2380 Schleswig, *Mahlsdorfer Str. 54, D-0-1170 Berlin
Postglacial Succession in the Subgenus Eubosmina (Crustacea: Ciadocera) in the Region of the Unterhavel River (near Berlin,
Germany) - Type Changes or Species Immigration?*
key words: Berlin lakes, Eubosmina Succession, immigration
Abstract
Analyses were made of subfossil Eubosmino remains from two Berlin Lakes. The first postglacial eubosminid was B. ( E . ) longispinu. In Tegeler See it occurred from the Allerod to Atlantic 2. In Lake Unterhavel it disappeared earlier in the Boreal. Bosmina (E.) longicornis occurred in early Atlantic I resp. at the end of Atlantic 2 (Tegeler See). Bosmina (E. ) c. coregoni appeared in Lake Unterhavel at the end of the Boreal, in Lake Tegeler See at early Boreal. Bosmina (E.) c. thersitrs occurred only in sediments of Lake Unterhavel beginning in Atlantic 2.
No sign of a “morphological transition” between taxa found by HOFMANN could be found in the two investigated lakes. The succession of Eubosmina taxa seems to be mainly the result of immigration.
Contents
I . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2. Investigated Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 3. Material and Methods; Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4.1 The region’s recent colonization by Euhosmina taxa . . . . . . . . . . . . . . . . . 5 4.2 Postglacial Euhosmina successions in Lake Tegeler See and Lake Unterhavel . . . . . 7 5. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 6. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
1. Introduction
It is well known that carapaces and head shells (incl. mucronae and antennulae) of planctonic Bosmina species are among the best conserved animal subfossils of lake sediments (FREY, 1955, 1967, 1986. HOFMANN, 1977, 1978a,b, 1980, 1984, 1986a,b, 1987a,b, 1991, GUNTHER, 1983, 1989, 1990 u.a.), and that analyses of them permit conclusions concerning typological changes of lakes since the Late Pleistocene and
-
* The paper is dedicated to the memory of Prof. Dr. David G. Frey.
2 J . GUSTHER and U. LIEDER
Early Holocene (BOUCHERLE and ZCLLIG, 1983, GUNTHER, 1983, FREY. 1955, HOFMANN, 1986a). Moreover, it is possible to evaluate actual problems of Bosmina taxonomy on the basis of subfossil remains, especially the so called ‘long term morphological variation’ and ‘phylogenetic transition’ among different Eubosmina taxa ( HOFMANN, 1977 p. 356) and from this their taxonomic ranks and the possibility of a.succession by time variable immigration of differing form types (species, subspecies, races) of the subgenus Eubosmina. A clarification of these problems is important not only for a review of the taxonomic ranking of different recent Eubosmina taxa, but also for the process of evolution in the subgenus Eubosmina.
2. Investigated Area
Lake Tegeler See is situated in the northwestern outskirts of Berlin in the Warzawa- Berlin ‘Urstromtal’. The age of the lake (from the Alleriid sands of the lowermost sediment layers) is estimated at roughly 13000 years (PACHUR & ROPER, 1987). Late Pleistocene and Holocene accumulation of sediments have reduced the maximum depth to 16 m. The area of Lake Tegeler See is 406 ha.
Postglacial Succession in Eubosmina 3
Figure 2. Catchment areas of Lake Tegeler See and Lake Unterhavel. A: = Area of the upper Havel River, range of distribution of B. (E.) C.E. morphotype diuphunu. B: = Area of the rivers Spree and Dahme. range of B. (E . ) C.C. morphotype rorwidu. C = Area with joint waters of the
rivers Havel, Spree and Dahme with diaphuna, rotunda and their intergrades.
The geology of the region and the developmental history of Lake Tegeler See and of neighbouring lakes is described by PACHUR & ROPER (1987). The lake's postglacial development from the analysis of animal microfossils is presented by SCHAKAU & FRANK, 1982 (Chironomidae) and GCNTHER. 1989 (Cladocera. Ostracoda, Chironomidae, and Chaoborus). The development of the diatomflora since Late Pleistocene can be seen in the paper of BERTZEN (1987).
The catchment area of Lake Tegeler See encompasses through the river Tegeler FlieD the northeastern parts of the Barnim high plateau (northern borderline of the 'Ustromtal') as well as all of the Oberhavel area as far as the region of Neustrelitz (Mecklenburg). and the lakes of the Miiritz region, joined together by the Miiritz-Have1 Canal. From time to time during high waters of the Spree River, the Spree-Dahme river and its lake region are added to the catchment of Lake Tegeler See, via the Berlin Spandauer Shipcanal (Hohenzollern Canal), built in the years 1848 to 1859.
The core from Unterhavel was taken downstream from the mouth of the Spree River south of 'Scharfe Lanke'. The Havel River there has the appearance of a river-lake. This lake-like character is presumed to have been caused by anthropogenic damming (Elbe River diking since 12th century; PACHUR & ROPER, 1987, pp 1 1 , 20); however, limnic sediments as well as the colonization of the waters by true limnoplankton since the Allerod indicate that at the boring location, water having a lake charactcr must
4 J. GUNTHER and U. LIEDER
Table 1. Trophic development of Lake Tegeler See and Unterhavel (GUNTHER, 1990)
Trophic status Tegeler See Unterhavel
(mesotrophic) eutrophic second half AT 2 first half AT 1
oligotrophic AL-AT 2 AL-B
highly eutrophic SB-SA2 phase
second half AT I-SA 2
have been present, certainly with strongly varying sedimentation rates as compared with Lake Tegeler See (GUNTHER, 1990). To the catchment of this lake-like part of the Havel River (Lake Unterhavel) belong as well as the waters of Oberhavel (upper part of Havel) as far as the Miiritz region, and also the numerous waters of the Spree and Dahme Rivers (Wendische Spree) east and southeast of Berlin as far as to the region of Cottbus.
Since the digging of the Oder-Have1 Canal and also the Oder-Spree Canal (about 1845) there exists a connection from the Havel and Spree Rivers to the Oder River system with its numerous lakes beyond the border in Poland. The study area is shown in Figure 1, the catchments in Figure 2.
According to the available analyses, the hydrologic and trophic development of Lake Tegeler See and Lake Unterhavel were different (G~NTHER, 1989, 1990). Both waters indeed changed their status from oligotrophic (or mesotrophic) to highly eutrophic but with a remarkable difference in time (Tab. 1). Today both waters can be classified as highly eutrophic.
3. Materials and Methods/Abbreviations
The core was obtained by Professor PACHUR and collaborators with a Livingstone borer (1953, improved after MERKT & STREIF (1970) and by the deep freezing technic of PACHUR et al. (1984).
Two cores were used for this investigation:
This core has a length of fully 30m. It comprises the first lacustrine sediments from the very beginning of lake formation in 29 m sediment depth and reaches until 3.65 m of sediment depth. The layers above 3,65 m were disturbed and could not be used for analysis. The age of the sedi- ment samples of Lake Tegeler See (T) are based upon dates of pollenanalysis (BRANDE, 1978/79).
For the analysis of the microfauna, 64 samples (sediment thickness 2-4cm) were chosen. They were selected according to the variability of the material and the availability of the core portions either continuously (Allerod) or at intervals of 10-30cm (Late Pleistocene) or 10-100cm (Postglacial). Each pollenzone was represented by at least four samples (4- 13). A subdivision of each sample in proportions of l g and a variable remainder was advantageous in terms of processing. An estimation of dried matter was performed on subsamples.
1. Lake Tegeler See: Core ‘Seetiefstes’ (T).
2. Lake Unterhavel: Core ‘Marina Lanke Werft’ (MLT). The boring was done in July 1988. The core was subdivided and 85 samples were stored for the
analysis of microfauna, of which 53 samples of 1 g were investigated. According to pollen analytic dating by BRANDE (l989), the earliest lacustrine sediments originate from the Allerod. Until Subatlantic 2 each pollen zone is represented by at least three (3-9) samples. The preparation of the samples’ was done following FREY (1959, 1976) and GUNTHER (1983). The samples were boiled for 20 minutes in 5% potassium hydroxide, subsequently screened and two fractions werc collected: > 2OOpm for shells of ostracods and headcapsules of chironomids, > I O O p r n for cladocerans ( 1 g samples only). The cladocerans were treated with 10% hydrochloric acid and
Postglacial Succession in Eubosmina 5
Table 2. Sediments of Tegeler See and Lake Unterhavel: Late- and Postglacial forest periods, duration of time, sediment depths, and cultural periods.
YbP Cultural Late- & Postglacial PZ Duration of SD/m Forest Period Time/Years T MLT Period AL = Allerdd I1 800 11750 Older
27.6 28.2 10950 Stone Age YD = Younger Dryas 111 700
26.8 25.8 10250 PB = Preboreal IV 1300 Middle
B = Boreal V 23.2 22.1 7950
AT1 =Atlantic 1 VI Is00
AT2 = Atlantic 2 VII 1500 Younger
SB = Subboreal VIII 2300 Bronze Age
SA I = Subatlantic 1 IX 1900
SA2 = Subatlantic 2 X 750
Ind = Industrialisation Recent Times
Abbreviations: T =core Lake Tegeler See, ‘Seetiefstes’ MLT=core Lake Unterhavel, ‘Marina Lanke Werft’ PZ= pollen zones: Late- & Postglacial forest periods (after FIRBAS) SD=sediment depth (m) ybp =years before present.
20.6 15.8 6450
15.9 8.2 4950 Stone Age
9.8 6.0 2650
3.9 750 Middle Ages
100
thereafter embedded in glycerol jelly. Each slide contains the cladocera in 0,l g wet sample. Cladocerdns were enumerated at a magnification of 80x. To facilitate comparison, the data obtained from the cores were adjusted to 1 g of dried material (g TS).
The representation of the recent Bosmina fauna was based upon information in the papers of RUHE (1912) and KEILHACK (1908, IW), as well as the analyses of zooplankton, carried out in the 1950s by U. LIEDER, encompassing most of the lakes (> 400) between the two rivers Elbe and Oder.
Table 2 gives a general summary of the sediment% of Lake Tegeler See (T) and Lake Unterhavel (MLT) in the respective pollen zones. It also gives most of the abbreviations.
4. Results
4.1. The region’s recent colonization by Eubosmina taxa
The recent Eubosmina taxa of the whole catchment area of lake Tegeler See as well as Lake Unterhavel (apart from regions beyond the Oder River) consist of two species with six subspecies and two infrasubspecific taxa. These Eubosmina taxa do not colonize the total region uniformly, because 1. their demands on the trophic status of the waters often differ markedly, 2. the special importance of the regionally different history of the taxa’s spreading. 3. the habit of closely related taxa either to exclude each other or to influence each
other mutually by hybridization and introgression.
Tabl
e 3.
D
istri
butio
n of
Eub
osni
inu
taxa
in
the
regi
ons
of S
pree
, Dah
me
and
Hav
el r
iver
s.
Taxo
n O
ccur
renc
e
Mec
klen
burg
er
Hav
el la
kes
Lake
Teg
eler
See
H
avel
lake
s La
kes
of
Lake
s of
So
litar
y la
kes
lake
dis
trict
no
rth-w
est
from
Ber
lin to
O
bers
pree
D
ahm
e in
Mec
klen
burg
(O
berh
avel
) of
Ber
lin
mou
th o
f H
avel
R
iver
R
iver
re
spec
tivel
y
Ode
r R
iver
R
iver
di
stric
t ne
ar
4
0
I)
B. (
E.)
c. c
oreg
oni
++
++
+
+
++
++
++
+
+
++
a)
B.
(E.)
c.c.
mor
phot
ype
b) B
. (E
.) c.
c. m
orph
otyp
e di
uphu
nu
++
++
+
+
++
+
+
0
0
++
c;
z -I I
rotim
du
0
0
++
+
+
++
++
+ rn
?J 01
3
0
0
0
0
0
(+I
+ 0
+ (0)
2)
B. (
E.)
c. gi
bher
u (+
) 3)
B
. (E
.) c.
the
rsite
s +
++
++
++
++
(+
) 4)
B
. (E
.) I.
lotig
icor
nis
0
+ +
(+I
5)
B. (
E.)
I. he
rolit
tens
is
+ 0
+ +
+
7)
B. (
E.)
crus
sico
rnis
(+
I 0
0
(( +
))
0
((+)I
(+I
(+)
a c c
++
++++
++
++
(+
I 6)
B
. (E
.) 1.
kess
leri
0
0
0
0
0
(+I
(+I
rn
0
Lege
nd:
+ +
+ +
pred
omin
ant,
at ti
mes
the
sole
inha
bita
nt
+ +
inte
gral
, at t
ime
an a
bund
ant e
lem
ent
+ fo
und
in s
ome
lake
s on
ly
(+)
very
rar
e, a
t tim
es o
ccur
ring
in o
ne la
ke o
nly
(( +
)) d
ied
out
since
190
0 0 ab
sent
(0)
erra
tic s
peci
men
s.
Postglacial Succession in Eubosmina 7
Table 3 and Figure 2 show the major aspects of the distribution of the respective taxa in the region of Spree, Havel, and Dahme rivers.
TO be disregarded is the morphologically very well characterized species B. ( E . ) crussicornis LILUEBORG, 1887. It still occurs only in lake Carwitzer See in the Feldberger region (Mecklenburg) (LIEDER, 1957, 1983b, FLOONER, 1972). In Lake Sacrower See near Potsdam (KEILHACK, 1908, 1909, ROHE, 1912, RAMMNER, 1926) it has died out since 1912 (LIEDER, 1957, 1983b, 1988).
B. ( E . ) longicornis kessleri UUANIN, 1874*, occurs only in a few lakes of Mecklenburg and Brandenburg, particularly at Neuruppin, Templin, Gransee, and Neust reli tz.
Nearly the same can be said of the even more seldom B. (E.) coregoni gibberrr SCHOEDLER, 1863, a taxon of the Baltic region with a markedly eastward spreading.
All the other Eubosminu taxa mentioned are important elements of the region's zooplankton. Of these taxa, Bosminu ( E . ) longicornis longicornis SCHOEDLER, I863*, is the least distributed. It is a typical Eubosmina of the'spree-Dahme river region, although it occurs only in a few lakes. In the region of the Havel River it is present from Lake Havelsee (north of Lake Tegeler See) to the mouth of Havel River in various lakes (including Lake Tegeler See).
The closely related subspecies B. (E.) 1. berolinensis IMHOFF, 1888*, whose presence excludes B. (E.) 1. longicornis*, can be found in the Miiritz region in Mecklenburg. in various lakes out of the Oberhavel river, in Lake Havelsee, Lake Tegeler See and further downstream in most of the lakes. It is furthermore a typical Euhosminu in the lakes of the Dahme and Oberspree rivers. Lake Muggelsee of the river Spree represents the typical locality of spp. berolinensis, river Spree of spp. longicornis.
B. (E.) coregoni thersites POPPE, 1887, has the same distribution (with exception of the Muritz region, Lake Havelsee and Lake Tegeler See). Morphologically it is a most remarkable Eubosminu.
Bosminu (E.) coregoni coregoni BAIRD, 1857, is by far the most frequent Euhosminu of the lake district between the Elbe and Oder rivers. LIEDER (1983b.) found it in nearly 78% of all lakes. Consequently, it is present in nearly all the lakes of the Havel region and the Spree-Dahme region, although it is less abundant in the typically, highly eutrophic and shallow 'Thersites lakes' (LIEDER, 1950) compared to the leading taxon B. ( E . ) c. {hersites and hence here can be regarded a marginal subspecies.
B. (E.) c. coregoni can be divided into two morphotypes. which were named rofundu by SCHOEDLER in 1865 and diaphuna by P. E. MUELLER in 1867. Both morphotypes differ quite a bit morphologically ( R ~ H E , 1912; LIEDER, 1957, 1983b. 1986, 1991). In the region under investigation the morphotype rotundu is the characteristic coregoni typc of the Spree-Dahme region (typical locality), whereas the Havel lakes upstream from Lake Havelsee, that means all of the coregoni lakes of the Mecklenburgian lake district. harbour the morphotype diuphanu. In the Havel River downstream from Lake Havelsee and Lake Tegeler See, diuphunu and rotunda are found together exhibiting mixed features probably as symptoms of not existing genetical isolation.
4.2. Postglacial Euhosminn Successions in Lake Tegeler See and Lake Un terha vel
Among the cladoceran remains occurring in sediments, carapaces of the genus Bosminu are among the best preserved. Besides Bosminu (Bosminu) longirostris (0. F. MUELLEK.
*The name of B. mixtu LILLJEBORG. 1901. does not correspondend with the nomenclatorical rulcs ( R ~ H E , 1912, p. 39, 41. LIEDER in press).
8 J. GUNTHER and U. LIEDER
Figure 3. Relative abundance of Bosmina ( B ) . longirostris. B. ( E . ) longispinu longispinu, B. ( E . ) longicornis, B. ( E . ) c. coregoni, and B. (E . ) thersites in core MLT of Lake Unterhavcl and corc T
of Lake Tegeler See (Chronozones and sediment depths are drawn to scale).
Postglacial Succession in Eubosminn 9
m
10 J. GUNTHER and U. LIEDER
1776), which has colonized both lakes since the Allerod with different eco- or morphotypes, in Lake Tegeler See and Unterhavel the following species, subspecies, and morphotypes of the subgenus Eubosmina SELIGO, 1900 were found: B. ( E . ) longispinu longispinu LEYDIG, 1860, (Fig. 4a,b) B. (E.) longicornis longicornis SCHOEDLER, 1865, (Fig. 4d,f) B. (E.) longicornis berolinensis IMHOFF, 1888, (Fig. 4c,e) B. (E.) coregoni coregoni BAIRD, 1857, morphotype diaphana P. E. MUELLER, 1867,
B. ( E . ) coregoni coregoni BAIRD, 1857, morphotype rotunda SCHOEDLER, 1865, (Fig. 5) B. (E.) coregoni fhersites POPPE, 1887, was found only in Unterhavel sediments. Plankton
analyses of Lake Tegeler See, done in the summer of 1989 confirm it's existence at Tegelort near the outlet of Lake Tegeler See into the Have1 River (GONTHER, 1988, not published). RUHE (1912, p. 115) has already
(Fig. 5 )
a
k k b
L
C
8
d
L L
Figure 5. Lake Unterhavel, core MLT Shapes of dorserventral shell corners resp. of bodyshells of B. ( E . ) cor'rgoni coregoni and B. (E . ) c. tlirrsitrs in different sediment layers. B. ( E . ) c. corqoni : a a n d e ) SD21,72mearly(AT l ) ,hand,f)SD 19.43m.candg)SD 14.30m (cndofAT l).tland 11) recent animals of lakes of River Unterhavel. B. (E . ) c. t/iersites, i ) SD 8,46 rn (end of AT 2), k )
recent animals of B. (E . ) c. tlwrsitcs.
Postglacial Succession in Eubosmina I 1
z so irb, m,
B.(E.l B. (E.1c.c. a(E.11. B.(E.Ic.c. B.(E. lc .c. Iongirqino dioqhano lonqirornis ro tundo I htrrilcr
brrolintno. -
SB
I I I I I 1 I I 1 I I I I I I t - r r r - r r r r r ) QO at M 92 LIL p6 PI UI u go 03 at 0.0 01 q r 0.0 0.2 o.r 96 0.0 1.0 1.z 1.t
11 0.6 .PI rtroins / 0.11 T S
Figure 6. Lake Unterhavel, core MLT: Euhosmina succession; remains in order of their
found several erratic specimens of B. ( E . ) c. thersires in the plankton from 1898 and 1910. (Fig. 5i.k)
In the sediments of both waters a succession of Eubosminu from B. ( E . ) 1. kongispintr and B. ( E . ) coregoni. morphotype ciiaplrana, via B. ( E . ) 1. longicornis and B. ( E . ) L'.
appearance in the sediment layers.
12 J. GCNTHER and U. LIEDER
z SI irb. n
1
SA 4
6 - SB
- 9
10
A T 2 12
11
16 -
1.3
AT1 10
- 21
B
PU - n
26 - YO
2% -
3@
At 3 E
Unterhavel MLT M a r i n a Lanke W e r f t
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... .... ... . . . . . . . . . . . . .... ... . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.:. . ' . . . . . . . . . . .
. . . . . . . . . . . . . . . . . *. I , .:... .<!!C . . . . . . . . . .
. . . . . . . . . . . . . . . . . . ....
. . . . . . .
number of inlennule segments
Figure 7. Gake Unterhavel, core MLT: Number of antennule segments (distal part) in relation to sediment depth (two points P one animal).
13 Postglacial Succession in Eubosmina
coregoni, morphotype rotwzdn could be followed. Since the end of AT2, B. (E.1 coregoni thersites was also found although restricted to Lake Unterhavel sediments.
Comparing the occurrence of Bosrnina (Fig. 3,6,7) in the sediments of Lake Tegeler See and Lake Unterhavel, there are evident differences despite similar successions.
1. Bosmina (E . ) c. coregoni, morphotype diaphana occurred in the sediments of Lake Tegeler See since the middle of the Boreal, and B. (E.) longispina population occurred together with B. (E.) c. coregoni morphotype diaphana until the middle of the Atlantic 2, differing in this regard from Lake Unterhavel.
2. Not before the middle of Atlantic 2 in Lake Tegeler See, in contrast to the first half of Atlantic 1 in Unterhavel does the constellation occur of morphotype diaphunu plus B. (E.) longicornis (longicornis or berolinensis).
3. From the middle of Atlantic I until the middle of Atlantic 2, which is a relatively short interval of time, Lake Unterhavel harboured an Eubosminu assembly that occurred in Lake Tegeler See not earlier than the transition Atlantic 2/Sub-Boreal: the morphotypes diaphana and rotunda together wiih B. (E.) 1. longicornis or berolinensis.
4. B. ( E . ) coregoni thersites occurred in Lake Unterhavel from end of Atlantic 2 but has not yet been found in the sediment of Lake Tegeler See.
5. Discussion
By it's holarctic distribution, B. ( E . ) longispina LEYDIG, 1860, demonstrates that it is a preglacial element of the fauna ofthe northern hemisphere (LIEDER, 1957,1982, 1983b), which was confirmed by investigations on Eem aged sediments in Denmark (FREY, 1962) and Pleistocene deposits in Canada (HANN & KARROW, 1983, HANN & WARNER, 1987). Today B. (E . ) longispina longispina in Europe belongs to the boreo-montane type of distribution, hence to the glacial mixed fauna (THIENEMANN, 1950) or to the assemblage of species along glacier margins (HOFMANN, 1980). with a distinct increase in abundance towards the east. In Central Europe 8. (E.) longispinu certainly colonized many, if not most of the lakes during the Pleistocene and in the Holocene until Boreal time occasionally into the Subatlantic. It was already present in the Baltic during the Ancylus Stadium (HOFMANN, 1987a). in the lakes of Holstein it was evident into the Boreal (HOFMANN, 1977, 1978a.b. 1984a. 1986a; GUNTHER 1983). In the eutrophic lakes of the Fore Alps, which presently lack B. (E.) longispinu, it was present in Postglacial (FREY, 1955, HOFMANN, 1984b, 1991). BOUCHERLE & ZuLm (1983) were able to verify its dieing out around the turn of century in lakes St. Moritz and Baldeggersec (Switzerland). Today we find in Central Europe north of the Alps merely some residual populations, most often in dystrophic moor waters of northwestern Germany, Belgium, and the Netherlands. The exponential decrease in number of waters during Postglacial time, the naturally occurring eutrophication of lakes, and, most important, the external impacts of civilization on the trophic conditions of the waters have deprived B. ( E . ) longispinu of its living conditions in large regions of Central Europe. It's increase in abundance towards the east might be connected not only with the larger number of still suitable waters there, but also with its approach to the Eurasian spreading center of this species.
The Occurrence of B. (E.) longispina longispinu in postglacial sediments of lakes located in the Warzaw-Berlin 'Ustromtal' was also expected and accordingly its presence in both Lake Tegeler See (G~NTHER, 1989) and Lake Unterhavel (GUNTHER. 1990) is not surprising. Based upon the mucrons at the ventrocaudal edges of the shell microfossils. it is possible to classify the populations of the morphic group urctiui- obtusirosrris-fucustris, which might be regarded as ecophenes (LIEDER, 1957. 1983b). I t
14 .I. GUNTHER and U. LIEDER
is interesting that B. (E.) 1. longispinu occurred in Lake Unterhavel from the Allerod until the Boreal, in Lake Tegeler See, however, until the middle of Atlantic 2 because of the lower trophic state of the lake and its more isolated hydrologic situation (GUNTHER, 1990).
It is of great significance in considering the possibility of a transformation of B. ( E . ) longispinu into the species B. (E. ) longicornis that absolutely no clues for this could be detected in the two cores. The subspecies B. (E . ) longicornis longicornis and B. ( E . ) 1. berolinensis have been detected in Lake Unterhavel at the onset of AT1 and in Lake Tegeler See toward the end of AT2 at sediment depths of 21.7m and 18.2m, respectively, hence at a time, when B. (6) longispina had already died out several hundred years and hence was lacking in the sediments. Although there does not exist one paleolimnological paper that casts doubt on B. (E . ) longispina being a ‘good’ taxon, and its transformation into B. ( E ) . longicornis is not taken into consideration, this finding, nevertheless, should be given due regard, because RUHE has removed the longspined species of his Longicornis-Insignis Group from B. (E.) longispina ( RUHE, 19 12, 191 3, 1914 after LIEDER, 1988). If these genealogical relationships should really exist or if all of the ‘Mixta’ group of species of the subgenus Eubosmina should be of hybrid origin with B. (E.) longispinu as one of the parental forms (LIEDER, 1957, 1983b), then such possible processes of evolution took place in the distant past and are not part of the history of the B. ( E . ) longispinu and B. ( E . ) longicornis populations in the late Pleistocene and Holocene.
Very interesting is the succession of the subspecies of B. (E.) corrgoni: ssp. coregoni, morphotypes rotunda and diaphana, and ssp. thersites. In Lake Tegeler See B. (E . ) c. coregoni was present as its morphotype diuphunu already about 9000 years ago in the Boreal (together with B. (E.) longispinu) at a sediment depth of 25m. It is still an abundant element of the lake’s fauna. At the beginning of the Subboreal 5000 years ago (lake depth 16m), the morphotype rotunda appeared in addition (with exception of single occurrences in the AT), and has populated the lake since then, whereby indications of failing genetical isolation between both morphotypes since the time of their sympatric occurrence (LIEDER & GUNTHER, not published) are present. Both mor- photypes of B. (E.) e. coregoni show that they are not only different morphologically (LIEDER 1957, 1983b, 1986), but also that they have different spreading areas. For example, the colonization of a large number of lakes in Canada and USA is accorn- plished only by a founder population of the morphotype rotundu of B. ( E . ) c. coregoni, which is a definite indication of genetic distinctness! In the area under investigation the morphotype represents the typical coregoni-Bosmina of the Havel River and its connected lakes and the morphotype rotunda that of the lakes of the Spree-Dahme region. After Lake Tegeler See established hydrological connection with Spree River in AT2 (G~NTHER, 1989). the Spree rotunda joined the lake’s autochthonous diuphuna.
During the time when B. (E . ) longispinu colonized Lake Unterhavel, B. (E.) coregoni was absent (Fig. 6, 7). It appeared first in AT1 at the same time as B. (E.) longicornis longicornis and B. (E . ) 1. berofinensis. An explanation of this time lag of appearance compared to that in Lake Tegeler See cannot be given at this time. The first settler was morphotype diaphana (SD 22, 1 m), which later on was joined by type rotunda ( S D 19,4 m). Both morphotypes permanently colonized the water in varying abundances, where here as in Lake Tegeler See, signs of failing genetical isolation can be detected. Both morphotypes of B. ( E . ) c. coregoni. including hybrid transitional forms occur today in the zooplanktion of all the Havel lakes (including Take Tegeler See and Havelsee), from the infiow of the Spree River to the mouth of the Havel River.
In Atlantic 2 (SD 9,4m) roughly 5000 years ago, remains of B. ( E . ) c. thersites appeared in the sediment of Unterhavel River without any transition, constituting since then a dominant Eirhosmina over B. ( E . ) c. coregoni. B. ( E . ) 1. longicornis and B. ( E . ) 1.
Postglacial Succession in Eubosmina 15
herohensis. I t should be noted for the latter subspecies (prespecies in the Sense of AYALA, 1978) that as in the recent distribution pictures of both Lake Tegeler See and Unterhavel they scarcely occur together at the same time but instead alternate, corresponding to the exclusion principle for closely related subspecies.
These results require a comparison with those of Eubosmina successions in lakes of eastern Holstein, communicated by HOFMANN. In case of B. ( E . ) longispina. HOFMANN ( 1 984a) detected in Lake GroBer Pldner See a transformation from B. longispina to B. refrexu (‘Because rejexu and fongispina forms are connected by unbroken transitional lines, without a morphological gap, these data clearly show, that the reJexa form arose by morphological variation of Bosmina longispina’, I984a, p. 298). Therefore HOFMANN considers rejexa merely as being a ‘forma’ of B. (E.) fongispina. Without discussing in this place the taxonomical distinctness of the ssp. rejexa, which should be beyond all doubt (LIEDER, 1957, 1983, RUHE after LIEDER, 1988), it should be emphasized that neither in Lake Tegeler See nor in Lake Unterhavel, there are any indications of a transformation of B. (E.) longispina.
Furthermore, HOFMANN (1976, 1978, 1984a) affirms from his materials a trans- formation of B. (€.) kessleri through a weakly mucronated B. (E.) coregoni to a rofundu like Bosminu in the course of post glacial development of several Holsteinean lakes. In addition, HOFMANN (1986b) describes in another Holsteinean lake a change from B. (E . ) c. coregoni to B. ( E . ) c. thersires, where in contrast to foregoing papers he considers not merely a simple type transformation but also species immigration and genetic processes.
In the case of Lake Constance (Untersee), HOFMANN (1991) recently abandoned his ideas concerning Bosmina transformations and offered for the first time convincing paleolimnological indications, in accordance with the concept held by LIEDER (1957, 1983b), MUCKLE & ROITENGATTER (1976), and EINSLE (1978). that in the Eubosrninu succession demonstrable in Lake Constance, species immigration and also the phenomenon of hybridization played a conspicuous role.
Without questioning HOFMANN’S results from Holsteinean lakes, it is nevertheless necessary to state that, from the point of view of Cladocera taxonomy, HOFMANN’S taxonomic concept cannot be accepted, Eubosmina species, subspecies and even races are well defined, morphologically distinct entities having highly stable morphological characters. In those localities where neither hybridization nor introgression takes place, uniformly connected water regions are settled by Eubosminu species that are alike in minute details (ROW, 1912, LIEDER, 1950, 1957, 1983, 1986). regardless of the lake types of that region (provided the trophic status allows establishment of the respective taxon (COITEN, 1985, PATALAS & PATALAS, 1961) and the intensity of predation pressure. The formation of local ecomorphoses plays only a subordinate role. Neighbouring but hydrologically separated water regions often differ in their Eubosmina races. Thus, a lake region, such as that of the Spree and Dahme rivers, can harbour a B. ( E . ) c. coregoni with straight antennulae, strictly hexagonal structuring of the shell, and a completely rounded ventrocaudal edge without seta kurzi (morphotype rotunda), while the neighbouring lake district, such as that of the total Havel River, houses a different B. ( E . ) c. coregoni, which is characterized by more bowed antennulae, a partial striping of the shell dorsally, and a ’sharp ventrocaudal edge’ with minimal set kurzi (morphotype diaphuna). Such features, which disregard all limnological pecularities and ecological constellations, are without any doubt expressions of genetic differences. They can be explained only by the history of the colonization of the waters (see also LIEDER, 1991, concerning B.c.c. in Canada and the USA). In no case is it SO, that ecological factors give a structure to a morphological continuum or that the Eubosminu taxa are plastic enough so that they can transform themselves from one morphotype into another one. This is possible only within the boundaries of the genetic
16 J. GOSTHER and U. LIEDER
‘Rcaktionsnorm’ enabling the transformation during the course of cyclomorphosis or during the formation of ecomorphoses (for which B. longispinu is particularly qualified). By this interpretation NAUWERCK’S (1991) results from Lake Mondsee can possibly be explained.
The authors prefer an interpretation of their opinion concerning the discrepancies of the succession problem in the following way: A simple explanation of the succession of Eubosmina as being morphological transformations is not possible for certain without comprehensive considerations of the postglacial history of the respective lake and its catchment area in its entirety, including hydrological peculiarities.
For example, in order to understand the successions and their origin in Lake Chiemsee (Bavaria) correctly, this lake must be regarded as one of the relict waters of the former Lake Rosenheim together with its former connections to other now isolated lakes, which might have ‘caught’ various taxa during waves of immigration. By analogy this is valid in our opinion also for the lake district of Plan in Holstein and its postglacial development (GROSCHOPF, 1936).
The Eubosmina successions discernible in Lake Tegeler See and Lake Unterhavel support unambiguously the idea of a settlement by varying taxa and at different times in the form of immigration waves, during which time the developing trophic conditions of the waters since the Allerod had a substantial importance. It is the same result that NAUWERCK (199 1) describes in the following words: ‘Immigration from elsewhere seems to be the primary reason for species succession. Suitable trophical conditions may allow newcomers to gain a foothold in the lakes’ (p. 102).
6 . Summary
During late glacial and postglacial history of Lake Tegeler See and Lake Unterhavel, a lake-like basin of Have1 River, both situated in the Wdrszawa-Berlin-‘Urstromtal’ near Berlin, Germany, a succession of Eubosmina taxa occurred. The analyses of the remains in two cores show that both lakes were inhabited by B. (E . ) longispina from the Allerod to the Boreal or to Atlantic 2. The species B. (E.) longicornis (ssp. longicornis resp. ssp. berolinensis) appeared at the beginning of Atlantic 1 (Unterhavel) or at the end of Atlantic 2 (Lake Tegeler See). Bosmina (E . ) coregoni is represented by the ssp. coregoni and thersites. In Lake Tegeler See B. ( E . ) c. coregoni and B. (E . ) longispina have coexisted from the early Boreal, when the lake was probably still oligotrophic, to Atlantic 2, when the lake became eutrophic and B. (E . ) 1. longispina disappeared. In Lake Unterhavel B. (E.) c. coregoni appeared later, at the end of the Boreal and beginning of Atlantic 1, together with the two subspecies of B. ( E . ) longicornis. In Atlantic 2, 5000 years ago when the lake was highly eutrophic, remains of B. ( E . ) c. thersites appeared in the sediments of Lake Unterhavel. All the mentioned species (except B. ( E . ) longispina) are components of today’s zooplankton in the lakes, (B. ( E . ) c. thersites only in Lake Unterhavel.
Two main problems are discussed, first the question whether the succession of Eubosmina taxa resulted from a morphological transformation or from immigration, and second the problem of the taxonomical state of the (infrasubspecific) coregoni taxa, either with a well rounded shell edge (‘rotunda’) or with a sharp edge (very short mucro), the so called ‘diaphana’, described by P. E. MUELLER in 1867.
The analysis of Eubosmina remains in Lake Tegeler See and in Lake Unterhavel makes it clear that immigration is the primary cause for the succession of taxa. There is not the slightest evidence for morphological transformation in the sense of HOFMANN, either in B. ( E . ) 1. longispina or B. ( E . ) longicornis or B. ( E . ) coregoni. For example B. ( E . ) c. thersires, a morphologically conspicuous subspecies with a giant humpback, is
Postglacial Succession in Eubosmina 17
not joined with B. (E . ) c. coregoni by a transformational change. Bosmina ( E . ) c. tliersites is clearly a subspecific (or specific) taxon and not a morphe of the coregoni subspecies.
The different morphotypes of the coregoni subspecies (rotunda SCHOEDLER. 1865 and diuphana P. E. MUELLER, 1867) are different in space as well as in time - in their presentday distribution in the Baltic region and in their time of immigration into these lakes.
Altogether the Eubosminu successions observed in two lakes of the Berlin area do not resemble the pattern found by HOFMANN in lakes of Holstein, North Germany. For this reason and for taxonomic reasons, the model of morphological transformations of eubosminids in the development of lakes and HOFMANN'S idea that a taxon can transform into another one (1978 p. 167, 174) are rejected.
7. Acknowledgements
Our acknowledgements are expressed to Professor Dr. PACHUR, Institut fur physische Geographie, Freie Universitat Berlin, who made it possible to perform analyses on microfossils. In addition J. GCJNTHER wishes to express her thanks to the DFG for financial support.
U. LIEDER feels very obliged to thank his begone superiors, the late Professor Dr. H. H. WUNDSCH and Professor Dr. W. SCHAPERCLAUS, who made it possible for him to perform investigations on cladocerans at the Institut fur Fischereiwesen, Humboldt Universitat Berlin, during the years from 1948 to 1963.
The authors thank also Miss KATJA T H ~ M I N G for drawing the figures, Dr. K. GUNTHER for translation, and especially the late Professor Dr. D. G. FREY, Department of Biology, Indiana University, Bloomington U.S.A., for carefully reviewing the manuscript, giving generously advice, and checking the language of the last draft.
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