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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)

Chapter 37. In search of Cypris and Cythere–A report of the evolutionary ecological project on limnic Ostracoda from Mondsee (Austria)

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486 D. L. DANIELOPOL,

ET AL.



/a

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.



TABLEI-MORPHOMETRIC

AND HYDROLOGICAL

PARAMETERS

OF THE MONDSEE.

Altitude

Surface area

Depth max.

mean

Volume

Theor. retention time

Mean discharge

Drainage basin



431 m a.s.1.

14.21 km*

68.3 m

36.0m

510,000,000 m3

1.7 years

9.2 m’lsec.

247 km2



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.

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

Megay, 1982).

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).



THELIVINGOSTRACODA

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.

TABLE

2-OSTRACODAOF r n MONDSEE.

~

-



Super-fam. Cypridacea

Fam. Cyprididae

Candona candida (O.F. Miiller)tz

Candona neglecta Sars t

Fabaeformiscandona caudata (Kaufmann)tz

Fabaeformiscandonaprotzi (Hartwig)t2

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)

Ilyocypris sp.

Super-fam. Cytheracea

Fam. Limnocytheridae

Limnocythere sancti-patriciiBr. and R0b.t'

Limnocythere inopinata (Baird)

LeJtcocytheremirabilis Kaufmannt

Metacypris cordata Br. and Rob.tl

Cytherissa lacustris (Sars)t2

Super-fam. Darwinulacea

Fam. Darwinulidae

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.



488



C



CY t h e r i s s a L a c u s t r i s



p

(J

1



"3



0sub-fossil valves

D 12-14cm El l i v i n g specimen

n= 3



D 12-14cm



0 16-18cm

nl5



1



D 18-20cm

n=173



31m

ST0



n=226



D 10-12cm

n=55



0



3



40m



(9.0784)






KL-30m



-=V V VI VII Vlll Ad

kL-45m



D 16-18cm

;="



1



D 18-20cm



-=V V VI VII Vlll Ad

BA-LO-47m






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).



TaxT-pro. 2-A.



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

other two.

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

A



m



TEXT-FIG.

3-A. Total abundances of Ostraoda at various depths for the transects MO-1 and MO-7.

I



B. Athndances of the main ostracod species at various depths of the transect MO-7.



490 D. L. DANIELOPOL.

ET AL.



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-



TEXT-FIG.

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%).



TEXT-FIG.

5-A, B. organogenic sediment from site MO-1/40 m; C, D. Candona neghcta, female, covered with

peritrichous Protozoa.



492 D. L.DANIELQPOL,

ET AL.



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

adult.

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.



493



A



MO-1140m N=108

n= 36



n=41



n=27



n= 6



n=4



n=62

80-



604020-



-5-7'8'AD



0-3



4



5-7 B E



3-



80-



.

60-



n=39



0-3 I 3-6

C M O - 7 1 40m N=100



1 6-9 I



9-12mn



-



0-3

80-



D



I



40



n=14



MO-7 / 20m

n=8



I



N=43

n=2



I



20

0



t



IAD



0-2



I



2-4



4-0



I



6-8



I



8-10mm



TEXT-FIG.

&Vertical distribution of Qtherissa lacustris in various sediment types (see explanation in text).



494



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

environment.

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

m.



496



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