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Chapter 37. In search of Cypris and Cythere–A report of the evolutionary ecological project on limnic Ostracoda from Mondsee (Austria)
486 D. L. DANIELOPOL,
TEXFFIG. 1-Lake Mondsee with sampling sites for subfossil ostracods. Short cores where 20 cm’ (circles) and
120 cm’ (triangles) have been analysed for each sediment depth; stippled areas show where Cytherissu
lacustris still lives.
OF THE MONDSEE.
Theor. retention time
431 m a.s.1.
Alps. It is surrounded to the south and west by limestone mountains and by morainic sediments;
the south-eastern side is situated in a flysch area (Text-fig. 1). The present lake originated about
17,000 years ago, after the melting of the Traun glacier which occupied the landscape during the
Wiirm period. Table 1 shows the most important morphometric and hydrological parameters of
The lake was for a long time an oligo-mestorophic one (Liepolt, 1935), well oxygenated and
sustaining, even in the deeper areas, a rich and diversified fauna. In the last 20-30 years, tourist
activity around the Mondsee has increased alarmingly with the inevitable consequence that the
water quality of the lake has deteriorated, especially in the north-western part of the lake in the
so-called Mondsee bay. Until 1968 the oxygen penetrated, even during the time of summer stagnation down to 60 m depth (Jagsch and Megay, 1982). After 1970, practically every year, there is in
the deeper parts of the lake a period of strong oxygen depletion (Muller, 1982). A slight eutrophication of the Mondsee has beEn recorded for the first time by Findenegg (1969). Since 1968 large algal
Limnic Ostraco& from Mondree, Austria 487
blooms,mainly of Oscillatoria rubescens and of various diatoms, have been recorded (Jagsch and
These facts have been documented recently by our interdisciplinary working group on the
Mondsee sediments, i.e. an increase in: the diatom abundances (Schmidt et al., 1985), the carotenoid paleopigments (Schultze, 1985), the total phosphorus and organic carbon (Helbig et al.,
1989, the abundancesof some of the benthic macrofauna like Oligochaeta (Herzig, 1985), a decrease
inthespeciesdiversity of Oligochaeta(Newrkla, 1985b), the disappearanceof some of the ecologically
sensitive ostracod species (Loffler, 1972; Danielopol et al., 1985). Irlweck and Danielopol (1985)
showed that the mean annual sediment accumulation rate is higher in the deeper zone of the
northwestern part of the lake (5-6 mm/yr) as compared with that of the shallower areas of the
Mondsee bay or even with the deeper zone of the southern part of the lake (2-3 mmlyr).
Kaufmann (1896, 1897) mentioned for the first time the presence in the Mondsee of Cytherissu
k t r i s , Leucocythere mirabilis and Limnocythere sanctipatricii, and Liepolt (1935) and Graf
(1938) also quoted, besides these species, Candona neglecta. During our three year investigation
we analysed more than 500 samples* which covered the entire lake.
2-OSTRACODAOF r n MONDSEE.
Candona candida (O.F. Miiller)tz
Candona neglecta Sars t
Fabaeformiscandona caudata (Kaufmann)tz
Pseudocandona sp. (cf. marchica ?)
Cypria lacustris S a d 2
Cyclocypris ovum (Jurine)
Herpetocypris reptans (Baird)
Isocypris beauchampi Paris
Prionocypris zenkeri (Chyser)t
Cypridopsis vidua (O.F. Miiller)
Potamocypris similis Miiller
Potamocypris villosa (Jurine)
Limnocythere sancti-patriciiBr. and R0b.t'
Limnocythere inopinata (Baird)
Metacypris cordata Br. and Rob.tl
Cytherissa lacustris (Sars)t2
Darwinula stevensoni Br. and Rob.
t1 only carapaces have been found; tZ ostracod species which occur in the deeper zone of the lake.
* We sampled with a modified Kajak-corer with an inner diameter of 5 cm devised by R. Niederreiter (Mondsee);
for qwlitative sampling we took 1-3 samples and for quantitative we took 6-8 replicate samples at each site.
CY t h e r i s s a L a c u s t r i s
D 12-14cm El l i v i n g specimen
-=V V VI VII Vlll Ad
-=V V VI VII Vlll Ad
M07- ( 1 2-40m)
Water content in the upper 2 cm of sediment from various sites and depths in the Mondsee.
B. Weight loss on ignition values from the samples used in A. C. Evolution of the age structure of the palaeopopulations of Cytherissa lucustrisfrom sites MO-3and MO-9as compared with those of living Cytherissa from
site MO-7 (V-VIII-instars).
Limnic Ostracoda from Mondsee, Austria 489
The ostracod fauna of the Mondsee (Table 2) is very similar to that of other pre-alpine lakes (see
data in Absolon, 1973; Loffler, 1972, 1975, 1978).
A first survey during the summer of 1982 allowed us (C.O.P.,
D.L.D. and M.-N.T.) to compare
the ostracod fauna from sites differing in sediment quality. The Mondsee bay has sediments
with a higher organic content (as expressed by the weight loss on ignition 550" C/2 h), and also
a higher percentage in water (we investigated the upper two centimetres of sediment) than the
central or southern parts of the lake. We compared the transect MO-1 from the Mondsee bay with
two other sites located off the bay, i.e. MO-3 and MO-7 (Text-figs. 1 and 2A, B). Our data show
that the total ostracod abundance and also species diversity are higher at site MO-7 when compared with those of MO-1 (Text-fig. 3A). The figures for MO-3 are intermediate between the
Several ostracod species which occur abundantly as subfossils in the deeper sediments of the
lake (i.e. Cytherissa lacustris, Limnocythere santi-patricii, Leucocythere mirabilis and Fabaeformiscandona cauduta) are rare in the lake and always in areas where the organic content is low;
oxygen situation during the summer stagnation does not become critical and the yearly sediment
accumulation rate is reduced (Danielopol et al., 1985). The deeper zone of the lake, which constitutes the largest area (Text-fig. l), is sparsely inhabited by ostracods (with the exception of site
MO-7/40 m). It seems that no permanent ostracod population lives at depths greater than 40 m.
The most common ostracod species in the whole lake are Candona neglecta, Fabaeformiscandona
protzi and Cypria lacustris. Cytherissa lacustris at site MO-7 at intermediate depths (10-20 m) occurs very abundantly when compared with other sites an ddepths (Text-fig. 3B). Limnocythere
3-A. Total abundances of Ostraoda at various depths for the transects MO-1 and MO-7.
B. Athndances of the main ostracod species at various depths of the transect MO-7.
490 D. L. DANIELOPOL.
sanctipatricii and Leucocythere mirabilis occur mainly in the southern part of the lake. Fabaeformiscandona cuadata reproduces parthenogenetically in most European and North American lakes.
In the Mondsee this species is amphigonic and, as a consequence, we are able to describe in detail
the morphology of the male.
The first general survey allowed us to select those species worthy of more detailed study.
Cytherissa lacustris, THE Drosophila OF PALAEOLIMNOLOGY
It is to the credit of Prof. H. Loffler that he demonstrated the importance of Cytherissa lacustris
as a potential palaeoecological indicator which can be used in the reconstruction of the oligotrophic
phase in pre-alpine lakes (Loffler, 1972,1975,1978,1983). It has become a tradition at the Limnological Institute of the Austrian Academy of Sciences to study the causes which result in the disappearance of Cytherissa lacustris in pre-alpine lakes. Before us Jager (1974), Powell (1976) and
Newrkla (1985a) have investigated aspects of this problem. We still do not know why this species
started to decline in abundance before the massive deterioration of the lake environment, e.g. the
occurrence of strong anoxic conditions, development of highly organogenic sediments (Loffler
1972, 1975; Danielopol et al., 1985). We also admit that, despite being able to make some
interesting observations on this species, we still know little of its autecology.
In this paper we present our preliminary observations on the macro- and micro-scale distribu-
4-A-D. Cytherissu lacustris. A. 7th juvenile instar; B-D.adults, female; B. inner valve anterior hinge
groove; C, D. right valve, exfkrnal side (arrow: the posterior node).
Limnic Ostracodafrom Modsee, Austria 491
tion of Cytherissa lacustris under field and laboratory-conditions. We expect to obtain from these
data a better idea of the local extinction of this species in the Mondsee.
The Macro- and Micro-scale Distribution of Cytherissa Zacustris
We first investigated the distribution of this species in the Mondsee on a macro-scale (metre
scale). We found that C. lacustris lives in sublittoral and deeper habitats from 3 m to 40 m depth
(Text-figs. 1 and 3B).
Large populations have been found in those areas where the sediment accumulation rate is low
(2-3 mm/yr) and the sediment is represented by fine sand (more than 20%) and silt-clay (60-80 %).
The sediments in the deeper zone of the northern and central part of the lake at depths greater
than 3 0 4 m are very fine grained (silt-clay fraction more than 90%).
5-A, B. organogenic sediment from site MO-1/40 m; C, D. Candona neghcta, female, covered with
492 D. L.DANIELQPOL,
Text-figures 5A and B show that these sediments are highly organogenic. Abundant bacterial
populations develop on the sediment type (Dokulil, pers. comm.).
We investigated the extent of the area from which C. Iacustris disappeared in the last 30 to 50
years, examining short cores from sites MO-1/30 m and 40 m, MO-3/43/44/45 m, MO-7/50-65 m,
MO-9/47 m*’, MO-1 (SCHW/3040 m), MO-3 (KL/30-46 m), MO-9 (BA-L0/40-47m)*2(Textfig. 1). In these samples we investigated the age structure of the palaeo-p~pulation*~.
Text-figure 2C shows that in the deeper layer C. lacustris is represented by all the postembryonic stages starting with the 4th instar, which one can find in the living population from site
MO-7 (Text-fig. 1). In the upper layers, an abrupt reduction in the number of valves occurs which
suggests that the population structure is disturbed down to its disappearance in the next layers.
We conclude from these data that Cytherissa lacustris disappeared from the deeper part of the
lake (deeper than 40 m) at least in the Mondsee bay, or in other words became locally extinct.
We approached the study of the spatial distribution of Cytherissu lacustris also at a micro-scale
level (mm and cm scale), as it is at this level that the ostracods most probably interact directly
with their environment. Traditionally it was believed that Cytherissa lacustris lives on the sediment
and penetrates into the superficial layers for only short periods of time. Powell (1976) showed that
this ostracod species normally lives in fine sediments, preferring those with a granulometry between
10 and 100 pm.
Loffler (1975, 1978) suggested that in the eutrophic lakes the deeper zone will become too fluffy
and the sedimentation rate will be too high to allow Cytherissu to live on the sediment; therefore,
it will slowly disappear from these types of habitats.
Our first interest therefore, was to check the validity of these hypotheses. We found that Cytherissa lacustris at site MO-7/20 m and 40 m depth lives mainly in the sediment down to 1-2 cm
depth (e.g. Text-fig. 6D). Powell (1976) showed that the sandy sediments above 200 pm are inimical to the “burrowing” ability of Cytherissu.
Our experiments showed that Cytherissu, which digs into the substrate, needs light grains in
order to penetrate inside the sediments. It is not the grain size which is decisive, but the quality of
the substrate and its texture. Cullen (1973) mentioned that ostracods can effectively bioturbate
marine sediments. We checked the validity of this process by culturing Cytherissu on different substrate types. Especially in fine glacial silty-clay sediments, one can see how Cytherissu lucustris
digs small tubes which remain open for several days. So a high density of Cytherissu can effectively
bioturbate the sediment. The first centimetre, especially, will be inhabited by about 90% of the
ostracod population (Text-fig. 6, MO-7/40 m, MO-1/40 m). The depth of penetration depends on
the compactness of the sediments. One should notice that in our experiments the sediments of site
MO-7/40 m were more mineralogenic and less compact which allowed the ostracods to penetrate
down to 18 mm depth (Text-figs. 6A-C).*4 The older instars (8th stage and the adult) penetrate
deeper than younger ones. Compared with site MO-7, the sediments of site MO-1/40 m (which we
used in our experiments) are very rich in diatom remains and agglutinate readily (Text-fig. 5A,B).
As Seki (1982) showed, this situation occurs commonly in eutrophic environments where microorganisms develop abundantly and exudate. The densest populations of Cytherissa lacustris at site
MO-7/12-20 m have a small number of specimens covered with sticky sediment (Text-figs. 4A, C,
D). The opposite is the rule in the case of Cytherissu lacustris from MO-7/40 m depth. Here three
10-20 cm’ sediment have been examined for 1-2 cm depth.
120 cm3sediment for every 2 cm depth.
We sieved the sample with a 100 pm sieve and we normally recovered the valves from the 4th stage up to the
For the study of the microvertical distributionwe used the method of Joint ef al., (1982), i.e. a syringe of
0.5 cm diameter; we sliced the sediment every 3 mm.
5-7 B E
0-3 I 3-6
C M O - 7 1 40m N=100
1 6-9 I
MO-7 / 20m
&Vertical distribution of Qtherissa lacustris in various sediment types (see explanation in text).
Limnic Ostracoda from Mondsee. Austria 495
times more specimens than in the former case are covered by fine mineralogenic and organogenic
particles (Pl. 1A-D).
We cultured Cytherissa lucustris on organogenic sediments from site MO-1/40 m and on natural
sediment from MO-7/12-20 m mixed with Cerophil (a laboratory food for microorganisms like
Protozoa). Plate 2A-D, shows that after several weeks, ostracods which have been on this latter
substrate are covered with fine sediments and/or with a dense bacterial film. Obviously these specimens will die, because they will be stuck to the sediment. In another experiment we placed specimens on fine sulphidic and organogenic sediment from site MO-1/40 m and found that after 4-7
days, some of the specimens moved slowly and could not close their carapaces. After 1-4 more days
they died with the carapace open. Several dissected specimens had fine particles of sediment stuck
between the limbs and on the inner side of the valve, especially diatom remains(P1s. lE, Fand 2E, F).
We made a similar observation with Candona neglecta, i.e. after one week some of our specimens
were densely covered with peritrichous Protozoa blocking their normal movement (Text-fig. 5C, D).
These observations suggest that the negative effect which can exterminate ostracod individuals
from a population is the structure and the composition of the fine sediment. However, we believe
that this is not the major constraining factor. Possibly the combination of low oxygen content at
the sediment-water interface as well as the sediment structure and composition together play the
major role in the decline, leading to the local extinction of Cytherissa lucustris in the deeper zones of
the Mondsee. This is the hypothesis that will be tested next by one of us (W.G.).
The Carapace Morphology and its Relationship to the Lacustrine Environment
The morphology of an organism (both in shape and in structure) is determined in most cases
by genetic and environmental factors (Ho, 1984). One of the directions for research in evolutionary ecology is to understand how the environment induces various ecophenotypes. For the
palaeoecologist this field of research is extremely interesting as one can use the ecophenotypes of an
organism for the recognition of different ecological parameters in past environments. As the morphology of an organism is induced by both genetic and epigenic (development) processes, it is
interesting to know if the resultant shape and structure have an adaptive value in the sense that they
represent a useful solution for the organism in order to facilitate its better integration into the
We investigated three aspects pertaining to these problems, i.e. the structure of the carapace
ornamentation, especially the production of nodes (mainly studied by M.T.F.), the variation of
the carapace size (investigated by W.G.) and the paedomorphic aspect of carapace shape (observations made by D.L.D.). Triebel (1951) noted that Cytherissa lacustris shows strong polymorphism
of the carapace. One can find carapaces with nodes and carapaces without nodes. C . lacustris can
develop up to seven nodes with different degrees of strength, from weakly to strongly developed
(Text-fig. 4A, C, D). Juveniles are particularly subject to torosity (Tolderer-Farmer, 1985). One
of the most persistent nodes is the one located on the ventro-posterior side. We demonstrate
elsewhere (Tolderer-Farmer, 1985; Danielopol e f al., 1985)that the percentages of noded Cytherissa
lucustris are higher at those sites where the lacustrine environment is rich in silica. We noted
(Danielopol et ul., 1985) that at site MO-4/10-15 m, the percentage of valves with a moderate
and/or strong posterior node represent 44% of the sample, whereas in deeper layers of the site
(MO-4/25-33 m) we found only 4 %. The sediments of the sublittoral and the deeper habitat of
transect MO-4 differ conspicuously in their quartz content. The former had twice the amount of
quartz than does the latter one, most probably due to the allochthonous impact of sediments
PLATE1-Cytherissa lacustris. A-D. Details of the carapace surface. A, B. Sieve pores moderately covered with
fine sediment and diatom remains. C, D. Carapace strongly covered with sediment. E, F. Living specimen
expost!d on organogenic sediment from the site MO-1/40