Europ. J. Protisto!. 33, 219-226 (1997)June 30, 1997

European Journal of

PROTISTOLOGY

On Functional Attributes of Testate Amoebaein the Succession of Freshwater Aufwuchs

Kurt JaxAG Limnologie, Institut fur Okologie, Friedrich-Schiller-Universitat Jena, Jena, Germany

Summary

The dynamics of testate amoebae in the Aufwuchs of asmall stream (11m, Thuringia, Germany) was investigatedover a two year period. Using experimental methods (ex­posure of artificial substrates) the specific performances oftestate amoebae species during succession were assessedand described as functional attributes. The most importanttaxa were classified according to dispersal ability, prefer­ence for particular phases of succession, and ability todominate the assemblages during late phases of succession.Comparison with previous work in standing water bodiesshowed both similarities and differences in the functionalattributes of testate amoebae with regard to succession inthe different aquatic environments. It was shown thatsome species have remarkably constant performancewhich might be used to indicate the successional status anddynamic characteristics of assemblages of testate amoebaein Aufwuchs.

Key words: Testate amoebae; Succession; Functional classi­fication; Freshwater; Streams.

Introduction

Species assemblages of protozoa are highly dynamic.The moulding of these assemblages is determined bymultiple variables and their specific patterns throughtime are difficult to predict. In spite of their short gen­eration times, succession of testate amoebae assem­blages on new or disturbed substrates often requiresseveral months before maxima of biomass or tempo­rary constancy of species composition patterns are at­tained. Moreover, succession does not proceed in aclearly deterministic manner when observed at thespecies level [5, 9J. Although it may not be possible topredict the exact species sequence during colonizationand succession of particular patches of substrate, itseems possible to characterize certain types of specieswhich occur typically during different stages of succes-

© 1997 by GustavFischer Verlag

sion. Earlier studies by]ax [4, 5, 9] about the dynamicsof testate amoebae in freshwater Aufwuchs demon­strated that testate amoebae can be clearly differentiat­ed with regard to their ability to colonize and persist inparticular phases of the successional development ofAufwuchs leading from bare areas (e.g, newly sub­mersed natural or artificial substrates or plant surfaces)to more or less dense covers of bacteria, protists andsmall plants and animals. Thus, a typification in termsof what may be called functional attributes related tosuccession can help predict the course of successions[5]. It may, if shown to be of greater generality, also beused to indicate the successional status of particular as­semblages of testate amoebae.

Typifications of protozoa have a long history. Theywere used mostly for purposes of bioindication. Kolk­witz and Marsson as early as 1908 [10, 11] used protozoato indicate the saprobic state of water bodies. Bick [1, 2]has classified ciliated protozoan species with respect totheir occurrence in particular states of the process ofself-purification of water, i.e. the succession occurring inresponse to the degradation of organic matter such ascellulose, peptone or unspecified organic sewage. Testateamoebae in the benthos of lakes Were typified with re­spect to their preferences for trophic conditions andhumus content of the sediment [15, 18, 19]. Meisterfeldwas able to classify testate amoebae in Sphagnum rela­tive to the water content in which they occurred [13].

Little is known, however, about the ecological pref­erences of testate amoebae in the course of dynamicphenomena, in particular primary succession both inpolluted and in unpolluted habitats. My previous stud­ies on the succession of amoebae in freshwaterAufwuchs have been carried out in standing water envi­ronments. Recently, investigations on the dynamics ofthese protozoa in a small stream (11m, Thuringia, Ger­many) provided the opportunity to compare the suc­cessional dynamics of testate amoebae in a lotic habitatto that observed in lentic ones. Thus, using the same

220 K. lax

methods as in the former study [5], functional at­tributes of testate amoebae were determined. This wasdone in order to see if the former results may be appliedto a broader range of ecological situations. This paperdiscusses the significance of the results with respect tothe ab ilities to assess successional state and dynamics ofassemblages of testate amoebae.

Sites and Methods

Study sitesThe 11m, Thuringia, is a small stream which orig inates in

the hills of the Thuringian Forest at an altitude of about 800 mNN. It flows mostly north-north-east and after about 135kmit empties into the Saale river (a tributary to the river Elbe)near GroBheringen (ca. 115 NN). The hydrological regime ischaracterized by per iods of high discharge during the periodof snow melting and occasional extreme flash floods in sum­mer (MQ (mean discharge) at the mouth 6 m3/s, HHQ (high­est discharge known) 100 m' Is) .

Investigations were carried out at two sites. The first site("Freibach") was in one of the headwaters of the 11m (streamkm 132), near Stiitzerbach, Thuringian Forest. There was anaverage gradient of 20%0 and a stream bed with coarse graveland single large stones . The long-term annual mean of thewater temperature was around 6.6 DC (SD 3.9), with a mini­mum of -2 DC and a maximum of 16 DC [14].The site was par­tially shaded by small trees. With the exception of occasionalinfluences by cattle on the nearby meadows, no pollutioncould be detected.

The second site ("Buchfart") was located at stream km 66.The gradient was 4%0 and the bed was covered with gravel andwith some small patches of detritus and mud. Water tempera­tures varied between 0 and 20 DC, with a long-term annualmean of 8.2 DC (SD 5.2) [14]. The shading was stronger thanat the Freibach site and there was also moderate organic pol­lution mostly from domes tical sewage of upstream villages.

MethodsTo provide a solid standard substrate of known surface

structure and area, artif icial substrates were used. Glass slides(76 x 26 mm) were arranged in vertical position close to thestream bed (see [16] for a detailed description of the appara­tus). One series of slides was exposed continuously and wasreturned to the same pos ition after each count ing of the tes­tate amoebae (long-term series). No more than 24 hourselapsed until the slides were returned to their original posi­tion. The other series, which was exposed close to the long­term series, was exposed only for a period of 4 weeks andthen renewed (short-term series). The overall duration of thestudy was 23 months.

All slides were transported to the laboratory in small glasscontainers filled with stream water and kept at approximatelytheir original temperatures. Counting was done at a magnifi­cation of 100fold with a Zeiss Axioplan microscope. Sixtyfields per slide were counted, the position s being selected ran­domly using a computer program. This amounted to ca. 10%of the slide area. Two adjacent slides were counted at eachdate.

Species biovolume estimates were based on p~blished data[5]. This procedure could be applied because occasional sam­ples showed that the sizes of the amoebae specimens in the11m were within the variation found in the previous investiga­tion.

To estimate the density of the overall Aufwuchs cover, thereduction of light transmission by this cover was measuredwith the light-meter of the microscope-camera (Zeiss MC100). Ten spots on each slide (objective 2.5x), always at thesame positions, were measured. The mean of these measure­ments was used to calculate a value for the Aufwuchs densityas an index according to the Lambert-Beer-Law.

Data processingThree classes of attributes which are considered to be of

importance for the performance of species during succession(functional attributes with regard to this specific phe­nomenon) were assessed for testate amoebae species of theAufwuchs assemblages.

Dispersal ability

The presence of the different species on the slides of theshort-term series and in the first 5 weeks of the long-term se­ries was used to assess the ability of species to disperse andcolonize new substrates rapidly. For each species the presencein percent of all slides analysed was calculated, without con­sidering numerical abundances. Slides not colonized by tes­tate amoebae at all were excluded from the calculations. Thevalue obtained (Vt-value) thus can also be regarded as a prob­ability of the early occurrence of this species if divided by100. From these data three types of dispersal ability (DA­types) were derived. Taxa occurring on less than 10% of theshort-term slides were classified as having small dispersalability (type k), those which occurred on more than 10% andless than 50% of the slides as having mean dispersal ability(type m) and those present on more than 50% were classifiedas having high dispersal ability (type g).

Phase of succession preferred

In order to distinguish between species which dominatedurin g the initial phase of primary succession and thosewhich show their highest abundances and dominance valuesin later phases of the successional development, a value Q wascalculated for each species according to formula 1:

n

I n,i = 1

Q=--J n

Dij is the dominance value of species j at the date i, n is thenumber of slides which were actually colonized. Values forlong-term series and short-term series were calculated sepa­rately; within the long-term series, only those slides exposedover a period of more than 5 weeks were considered. To avoidan overestimation of amoebae occurring only by chance, onlyslides with more than 50 specimens were considered as colo­nized and the others excluded. The result of these calculationsthus is an average dominance of the parti cular species regard­ing the n colonized slides of each series.

The calculations were carried out on the basis of specimenabundances as well as on the basis of biovolumes. In the next

step values of long-term and short-term series were com­pared. As a consequence each species was attributed to one ofthree types with regard to the successional phase preferred(PP-types). If the average dominance of the particular specieswithin the long-term series was more than two times as highas that of its corresponding short-term series, the species wascategorized as a late successional species (type SP), In the op­posite case (ratio of average long-term dominance to short­term dominance <D,S) the species was classified as an earlysuccessional species (type F); if no unambiguous differencesof this kind were detected, the species was termed "tolerant"(type T).

The decision to compare dominances instead of abun­dances is based on the consideration that abundances aremore strongly affected by non-successional variations in theoverall Aufwuchs density than are dominances.

Dominance in late stages of succession (Overalllong-term dominance)

This value provides a comparison of the different speciesencountered with respect to their ability to dominate later

Attributes of Testate Amoebae 221

successional stages of the species assemblages. The calcula­tions are based on the average dominance values of the long­term series according to formula 1. The overall long-termdominance values (D,,-values) can be interpreted as providinginformation on how well a particular species is able to estab­lish itself within a testate amoebae assemblage.

The different values are classified into three categories(long-term dominance types = LTD types): D" < 1: class I,1 < D" < 10: class II, and D" > 10: class Ill. Although valueswere calculated and tabulated both for specimen numbers andbiovolumes, only the latter were used for ordinal classification.

Results

25 taxa of testate amoebae were recorded and listedin Table 1. Most species are commonly encountered inthis kind of habitat. Figures 1 and 2 display the tempo­ral dynamics of the overall Aufwuchs cover and of thetestate amoebae abundances and biovolumes. Both ofthe long-term series were destroyed by ice and high

Table 1. List of testate amoebae taxa encountered on glass slides in the Ilm,

Species

CochliopodidaeCochliopodium bilimbosum cf. (Auerbach, 1856) Leidy, 1879MicrocorycidaeMierochiamys patella (Claparede & Lachmann, 1859) Cockerell, 1911Mierochiamys spec.ArcellidaePyxidiculaoperculata (Agardh, 1827) Ehrenberg, 1838Arcellaconica (Playfair, 1917) Deflandre, 1928Arcelladiscoides Ehrenberg, 1871Arceliadiscoides v.foveosa Piayfair, 1917ArceliagibbosaPenard, 1890Arcella hemisphaerica Perty, 1852Arcella vulgaris Ehrenberg, 1830CentropyxidaeCentropyxisaculeata (Ehrenberg, 1830) Stein sec. Penard, 1859Centropyxisaerophiia Deflandre, 1929CentropyxishirsutaDeflandre, 1929Centropyxisplatystoma (Penard, 1890) Deflandre, 1929DifflugiidaeDifflugia spec.LesquereusiidaeQuadrulella symmetrica(Wallich, 1863) Cockerell, 1909PhryganellidaePhryganella aeropodia (Hertwig & Lesser, 1874) Cash & Hopkinson, 1909Phryganelia paradoxa Penard, 1902EuglyphidaeEuglyphacf acanthophora (Ehrenberg, 1841) Perry, 1852EuglyphatuberculataDujardin, 1841Trinema lineare Penard, 1890CyphoderiidaeCyphoderiaampulla (Ehrenberg, 1840) Schlumberger, 1845GromiidaeLecythium hyalinum (Ehrenberg, 1838) Hertwig & Lesser, 1874Plagiophrys spec.Pseudodifflugia gracilis Schlumberger, 1845

Freibach

xx

xxxx

x

xxx

x

x

xx

x

x

x

x

Buchfart

x

x

x

xxxxx

xxx

x

xx

xx

x

xxx

222 K. Jax

4

3

2

800

600

400

200

Aufwuchs density

testate amoebaenumber per sl ide

2-r-------,--------------,Auf wuchs density

4000

2000

20

10

testate amoebae Ibiovolume per sl ide (,um3 x 106)

II

IIIIIII

300

200

100

testa te amoebaebiovolume per slide l}Jm3 x 106)

Fig. 1. Dynamics of Aufwuchs cover and testate amoebaeassemblages on glass slides at the Freibach site (long-termseries). The two slides counted at each date are displayedseparately.

discharges during winter 1992/93 and had to be restart­ed. At the Buchfart site a flood in the autumn of 1993destroyed the equipment again. It could not be re-es­tablished during the investigation period.

Colonization of the slides was highly episodic. In allcases, the populations of testate amoebae collapsed dur­ing late fall. The reasons are not clear. The low tempera­tures are not a likely explanation for thIs phenomenon,as the same taxa are able to survive and to reproduce inlentic environments, even under ice cover [5]. This im­plies that the accelerating flow during the autumnmonths is more important.

The Aufwuchs cover as a whole was much denser atthe Freibach site than at Buchfart. At Freibach it con­sisted mostly of various filamentous algae and cyano­bacteria, while in Buchfart detritus and adnate unicellu­lar algae (mostly Cocconeis spec.) were the mainAufwuchs elements. During the course of the monthsthe slowly growing cyanobacteria developed a darklayer firmly attached to the glass, which even resistedabrasion with a thumb nail. This rise of the"Aufwuchsdensity" in the autumn and winter of 1993 is at-

Fig. 2. Dynamics of Aufwuchs cover and testate amoebaeassemblages on glass slides at the Buchfart site (long-termseries). The two slides counted at each date are displayedseparately.

tributable to these cyanobacteria. The rise of theAufwuchs density at the site Buchfart beginning frommid-June 1993 is also in part due to the deposition offerrihydroxide.

Testate amoebae abundances roughly .paralleled thetendencies of the whole Aufwuchs cover. However, nocorrelation between testate amoebae density and that ofthe overall Aufwuchs could be shown (Figs. 1 and 2).Although the cover was always less dense at Buchfartthan at Freibach, testate amoebae densities were muchhigher at Buchfart. This is even more pronounced if.thetotal biovolumes of testate amoebae on the slides arecompared. Additionally, grazing activity by snails andchironomids was higher at the Freibach site.

For the typification of the testate amoebae onlyseven species were considered. These species were com­mon and abundant enough to be evaluated. Theyamounted to between 70 and >90% of total abundanceand biovolume on all series. Table 2 depicts dispersalability as measured by the presence of different taxa onthe short-term slides. Note the considerable differencesbetween the values obtained at Freibach and at Buch-

Attributes of Testate Amoebae 223

Table 2. Dispersal abilit y values (VJ and derived ordinal type s (DA -types) of selected taxa of testate amoebae in the Ilrn. N =sample size, g =high dispersal ability, m =medium dispersal ability, k =low dispersal ability. See text for calculation of Vt-values

Disp ersal Ability Freibach Buchfart Combined(N =20) (N =25) (N =45)

Species VrValue DA-Type VT-Value DA-Type VrValue DA-Type

Microchlamys patella 25 m 60 0- 44.89 m"Pyxidicula operculata 15 m 52 g 44.44 m

Arcella discoides var. fo ve osa 15 m 48 m 33.33 mCentropyxis aerophila 30 m 20 m 24.44 mCentropyxis hlrsuta 20 m 36 m 26.67 mPhryganella acropodia 10 m 4 k 6.67 kPhryganella paradoxa 95 g 76 g 77.78 g

Table 3. Comparison of average dominances of selected test ate amoebae taxa on slides of the short-term and long-term series atthe Freibach site. PP-Type: preference of particular phases of succession . F = early species, SP = late species, T =tolerant species.LTD-type: overall long-term-dominance, ranging from I (low) to III (high). See text for modes of calculation and ordinal classi­fication

Freibach Specimen Numbers Biovolumes Typification

Species Short-Term Long-Term Short-Term Long-Term PP-Type LTD-Type

Microchlamyspatella 3.9 0.72 2.46 0.74 F IPyxidicula opercu lata 10.78 1.72 0.49 0.12 F IA rcella discoides var. foveosa 2.28 2.39 8.87 4.11 T IICentropyxis aerophila 7.99 7.36 23.27 16.97 T IIICentropyxis hirsuta 0.14 10.34 1.76 27.65 SP IIIPhryganella acropodia 0.00 0.87 0.00 1.97 SP IIPhryganella paradoxa 56.62 69.31 33.36 30.31 T III

Table 4. Comparison of average dominances of selected testate amoebae taxa on slides of the short-term and long-term series atthe Buchfar t site. PP-Type: preference of particular phases of succession . F = early species, SP = late species, T = tolerant species.-LTD-type: overall long-term-dominance, ranging from I (low) to III (high). See text for mod es of calculation and ord inal classi­fication

Buchfahrt Specimen Numbers Biovolumes Typification

Species Short-Term Long-Term Short-Term Long-Term PP-Type,/ LTD-Type.>

Microchlam ys patella 15.16 2.00 19.20 0.55 F IPyxidicula operculata 36.86 0.88 13.68 0.06 F IArcella discoides var. fov eosa 4.22 16.21 17.02 17.86 T IIICentropyxis aerophila 1.76 0.70 4.7 1.5 F IICentropyxis hirsuta 0.97 22.98 9.85 55.93 SP IIIPhryganella acropodia 0.09 7.99 0.36 4.57 SP IIPhryganella paradoxa 38.69 42.15 25.93 10.09 T III

fart. Tables 3 and 4 display the results obtained for thephases of succession preferred by the different species.Data for the Freibach site and the Buchfart site werecalculated separately. Both average percentages on theshort-term slides and on the long-term slides are given.At Freibach the sample size was 14 slides for the long-

term series and 10 slides for the short-term series. Atthe Buchfart site IS slides of each series could be usedfor the calculations. As described above, the averagedominance of each species on the long-term slides isalso the basis for the classification of the overall long­term dominance attribute.

224 K. lax

Table 5. Comparison of functional attributes of testate amoebae obtained from the current study and from investigations instanding water bodies [5]. See Table 2-3 for explanation of abbreviations

Attribute Dispersal Successional Phase Overall Long-Ability Preferred Term-Dominance

Species ILM JAX 1992 ILM JAX 1992 ILM JAX 1992

Microchlamys patella m g F F I IIPyxidiculaoperculata m g F F I IArcelladiscoidesvar.foveosa m m T F III ICentropyxsisaerophila m m T I II ICentropyxishirsuta m g SP SP III IIIPhryganellaacropodia k g SP T II IIIPhryganellaparadoxa g g T F III II

Discussion

The present results are compared and contrastedwith previous studies of standing waters [5] and aresummarized in Table 5. The current in the small streamdoes not enable a more rapid colonization but ratherseems to impede colonization by the protists on thesesubstrates. Most species were observed to colonizeslower (i.e. they were rated to have a lower dispersalability) in the Ilm than in lentic environments (Table 5).Additionally this tendency is much more conspicuousat the upstream site (Freibach) with its lower watertemperatures and much more variable discharge incomparison to the more benign lower site at Buchfart(Table 2). Even at Buchfart "later" species colonizedless effectively than in standing water bodies; at theFreibach site this tendency is much stronger. OnlyPhryganella paradoxa could be rated as a g-species(high dispersal ability) there.

Compared to the data of the previous study [5] therating of the phase of succession preferred was the samefor three taxa while it differed for three other taxa (Fig.5). Phryganella acropodia, which was classified as pre­ferring late phases of succession in the Ilm in contrast tobeing rated as a tolerant species i~ lentic environments,showed, however, a slight but not pronounced tenden­cy towards later stages of succession also in standingwaters [5]. Again, the types at Buchfart resembled moreclosely that in standing waters.

The data indicate that Phryganella paradoxa is ableto gain high dominances even in terms of biovolumes inthose cases where dominants like Centropyxis hirsutacannot recruit successfully. This phenomenon wasmore pronounced at Freibach, where the colonizationproceeded slower than at Buchfart (d. Tables 3 and 4).The very small body size enables this species to multi­ply very rapidly and it may also gain advantage by itsability to utilize small spaces in Aufwuchs, providingshelter from many grazing animals.

Of the seven species examined, three showed consid­erable constancy in their performances during succes­sion in different habitats. Microchlamys patella andPyxidicula operculata are pronounced primary coloniz­ers with good dispersal abilities. They can never befound in higher numbers and dominances during laterphases of succession, at least if there are no localizeddisturbances (sensu [21]). In particular Microchlamyspatella may also colonize small open patches inAufwuchs as produced for example by small grazinganimals. Centropyxis hirsuta, on the other hand, is atypical dominant of later stages of.succession.

I could find no published data on the characteristicamoebae species of early successional stages. With re­spect to later stages of succession Schonborn [17] re­ports Centropyxis aculeata and Phryganella acropodiato be dominant species on glass slides exposed for sev­eral months in the river Saale.

The species which have been evaluated in the Ilm interms of their performance during successional pro­cesses are ubiquitous in freshwater environments. OnlyPyxidicula operculata has been reported rather infre­quently in the literature. This might, however, be at­tributed mostly to the fact that this species is easilyoverlooked and confused with algae. I was able to findPyxidicula in almost every freshwater environment ([3,4] and jax, unpublished observations).

The broad distribution of the taxa considered in thisstudy is an important prerequisite for their use as a kindof bioindicator. As such these amoebae might indicatethe successional status of species assemblages and pos­sibly the degree of the dynamics of these assemblages asgiven by different disturbance regimes (sensu [21]; seealso [6-8]). Assemblages with frequent disturbances aresupposed to be characterized by a higher percentage ofearly species (e. g. Microchlamys patella) while a de­crease in disturbance frequency and intensity will fos­ter later species (e. g. Centropyxis hirsuta). Thus, thecomposition ,?f natural testate amoebae assemblages

may indicate the degree of dynamics they experiencedin the past.

The specific performance of the different taxa ascharacterized by the typification described has alsoconsequences for the species composition and diversityof whole species assemblages (in terms of species num­bers or Shannon-Weaver diversity) with respect to dif­ferent disturbance regimes. This is indicated by investi­gations on natural substrates from the same site [8] andalso by the first results of a modelling approach basedon data from this study and that of a former study by]ax [5], which has been developed by Larsen [12]. Itcould be shown that species persistence and diversitypatterns of whole assemblages are determined by an in­terplay between several variables. These were the dis­turbance regime (as given by hydrological events),properties of the benthic substrates, and specific prop­erties of different types of testate amoebae as describedabove. Body size was added as a further parameter tothe functional characterization of each species.

Conclusion

Data on functional attributes of testate amoebaefrom standing waters, where Aufwuchs could developfor much longer in rather undisturbed conditions, canserve as a standard against which the species assem­blages from other sites should be evaluated. This can beconcluded in spite of some differences between speciesperformances in lotic as compared to those in lentic en­vironments. The functional attributes of several com­mon testate amoebae species thus seem not to be con­fined to succession in one kind of aquatic habitat, al­though further investigations are required to assess thedegree of generality of these results.

The relative abundances of taxa belonging to differ­ent functional types as characterized by the attributesof dispersal ability, phase of succession preferred, andlong-term-dominance can give valuable insights intothe dynamics of the Aufwuchs assemblages. These re­sults can also foster the formulation of hypotheseswhich may be subjected to experimental testing. How­ever, additional data would be very valuable, both fromthe field and from the laboratory. Questions of interestpertain to the role of (constant) currents on the condi­tions for colonization (see e.g. [20] in a study about theconditions of algal colonization) or the influence ofsmall scale disturbances and size-selective grazing onthe species composition of successional assemblages.

Acknowledgements: I wish to thank Mike Traynor,Ashord, Connecticut, for his valuable help in clarifying andimproving the language of this paper. This study was sup­ported by the Bundesministerium fur Forschung und Tech­nologie (Forderkennzeichen 0339310 F).

Attributesof Testate Amoebae 225

ReferencesBick H. (1964): Die Sukzession der Organismen bei derSelbstreinigung von organisch verunreinigtem Wasserunter verschiedenen Milieubedingungen. Modellversucheunter besonderer Berucksichtigung der Ziliaten. DerMinister fur Erniihrung, Landwirtschaft und Forsten desLandes Nordrhein-Westfalen, Dusseldorf.

2 Bick H. (1973): Population dynamics of Protozoa asso­ciated with the decay of organic materials in fresh water.Am. Zool. 13, 149-160.

3 Jax K. (1985): Beitrag zur Rhizopodenfauna des Rhein­lands (Protozoa, Rhizopoda). Decheniana 132, 182-191.

4 Jax K. (1985): Remarks on the ecology of Pyxidicula oper­culata (Agardh) Ehrenberg. Hydrobiologia 124,263-268.

5 Jax K. (1992): Investigations on succession and longtermdynamics of Testacea assemblages (Protozoa: Rhizopoda)in the Aufwuchs of small bodies of water. Limnologica 22,299-328.

6 Jax K. (1994a): Renaturierung kleiner FlieBgewiisser.Moglichkeiten und Probleme einer Einbeziehung desKonzepts der natiirlichen Storungen, In: Grunewald U.(ed.): Wasserwirtschaft und Okologie, UmweltWissen­schaften Bd. 2, pp. 118-126. Blottner-Verlag, Taunusstein.

7 Jax K. (1994b): Untersuchungen zur Dynamik des Mikro­zoobenthon in der Ilm als Mittel zur okologischen Be­wertung von FlieBgewiissern. In: Deutsche Gesellschaftfur Limnologie (ed.): Erweiterte Zusammenfassungen derJahrestagung 1993 in Coburg, pp. 482-486. KaltenmeierSohne, Krefeld.

8 Jax K. (1995): Die Dynamik von Organismengemein­schaften des Mikrozoobenthons (Rhizopoda, Testacea) inder Ilm. Ein Ansatz zur Beriicksichtigung nattirlichcrStorungen bei der okologischen Bewertung von FlieB­gewiissern. In: Forschungsbericht "bkologisch begriin­detes Sanierungskonzept der lIm (Thiiringen) mit derZielstellung der weitgehenden Renaturierung des FlieB­gewiissers und seiner Aue". Bundesministerium furForschung und Technologie, Forderkcnnzeichen 0339310F, Vol. 2, pp. 353-397.

9 Jax K. (1996): The influence of substratum age on patternsof protozoan assemblages in freshwater Aufwuchs - acase study. Hydrobiologia 317, 201-208.

10 Kolkwitz R. and Marsson M. (1908): Okologie der pflanz­lichen Saprobien. Ber. Dtsch. Bot. Ges. ?6a, 509-519.

11 Kolkwitz R. and Marsson M. (1m): Okologie der tieri­schen Saprobien. Int. Rev.Jgesamten Hydrobiol. 2,126-152. ,

12 Larsen M., Jetschke G., and Jax K. (1995): Modellierungder Dynamik der benthischen Besiedlung in kleinenFlieBgewiissern (am Beispiel der Ilm) und deren Ab­hiingigkeit von iiuBeren Storungen, In: Forschungsbericht"bkologisch begrundetes Sanierungskonzept der Ilm(Thuringen) mit der Zielstellung der weitgehenden Rena­turierung des FlieBgewiissers und seiner Aue". Bundes­ministerium fur Forschung und Technologie, Forder­kennzeichen 0339310 F, Vol. 2, pp. 398-412.

13 Meisterfeld R. (1977): Die horizontale und vertikaleVerteilung der Testaceen (Rhizopoda, Testacea) in Sphag­num. Arch. Hydrobiol. 79,319-356.

14 Polz S. and Moller U. (1995): Die Auswertung von Alt­. daten (1976-1989) physikalischer und chemischer Para­meter im Liingsverlauf der Ilm. In: Forschungsbericht"bkologisch begrundetes Sanierungskonzept der Ilm

226 K. lax

(Thuringen) mit der Zielstellung der weitgehenden Rena­turierung des Flieisgewassers und seiner Aue". Bundes­ministerium fur Forschung und Technologie, Forder­kennzeichen 0339310 F, Vol. 1, pp. 66-84.

15 Schonborn W. (1966): Testaceen als Bioindikatoren imSystem der Seetypen. Untersuchungen in masurischenSeen und im Suwalki-Gebiet (Polen). Limnologica(Berlin) 4,1-11.

16 Schonborn W. (1976): Das Periphyton der mittleren Saale.Limnologica (Berlin) 10,97-122.

17 Schonborn W. (1981): Populationsdynamik und Produk­tion der Testaceen (Protozoa: Rhizopoda) in der Saale.Zool.Jb. Syst. 108,301-313.

18 Schonborn W., Flossner D., and Proft G. (1965): Die lim­nologische Charakterisierung des Profundals einiger nord­deutscher Seen mit Hilfe von Testaceen-Gemeinschaften.Limnologica (Berlin) 3, 371-380.

19 Schonborn W., Flossner D., and Proft G. (1966): Die lim­nologische Charakterisierung des Profundals einiger nord-

deutscher und masurischer Seen mit Hilfe von Testaceen­Gemeinschaften. Verh. Int. Ver. Limnol. 16,251-257.

20 Stevenson R. J. (1983): Effects of current and conditionssimulating autogenically changing microhabitats on ben­thic diatom immigration. Ecology 64,1514-1524.

21 White P. S. and Pickett S. T. A. (1985): Natural distur­bance and patch dynamics: An introduction. In: Pickett S.T. A.and White P. S. (eds.): The ecology of natural distur­bance and patch dynamics, pp. 3-13. Academic Press, SanDiego.

Address for correspondence: Kurt Jax, Friedrich-Schiller­Universitat Jena, Institut fur 6kologie, AG Limnologie,Winzerlaer Str. 10, D-07745 Jena, Germany. Tel.: (+49) 3641/65 75-90, Fax: (+49) 3641/65 76-00E-mail: b5kuja@rz.uni-jena.de