Monitoring macroinvertebrates in the River Rhine. Results of a study executed in the Dutch part in 1990.

Transcription

1 Monitoring macroinvertebrates in the River Rhine. Results of a study executed in the Dutch part in 0. To be cited as: Bij de Vaate, A. & M. Greijdanus-Klaas,. Monitoring macroinvertebrates in the River Rhine. Results of a study executed in the Dutch part in 0. Report no. - of the project 'Ecological Rehabilitation of the rivers Rhine and Meuse', pp. Institute for Inland Water Management & Waste Water Treatment, Lelystad, The Netherlands. Participating institutes in the project: Onbehalf of theministryoftransport,publicworks &Water Management: Institutefor Inland WaterManagement &WasteWaterTreatment (RIZA), P.O.Box,NL-00AALelystad,TheNetherlands Onbehalf of theministryof Housing,PhysicalPlanningand Environment: National Institutefor PublicHealthand Environmental Protection (RIVM), P.O.Box,NL-0BABilthoven,TheNetherlands. Onbehalf of the MinistryofAgriculture,NatureManagement andfisheries: Netherlands Institutefor Fishery Investigations (RIVO-DLO), P.O.Box,NL-0ABUmuiden,TheNetherlands. Institutefor Forestry &NatureResearch (IBN-DLO), P.O.Box0,NL-0 HBArnhem,TheNetherlands. TheWinand StaringCentrefor Integrated Land,Soil &Water Research (SC-DLO), P.O.Box,NL-00ACWageningen,TheNetherlands.

2 CONTENT. SUMMARY INTRODUCTION STUDYAREA STUDYLOCATIONS METHODS RESULTS * Stonesin the littoral zoneof the groynes and riverbanks * The riverbottom * Assessment ofwater quality DISCUSSION LITERATURE APPENDIX APPENDIX APPENDIX APPENDIX APPENDIX page

3 SUMMARY. As a result of an initiative of the working group Kö of the International Commission for protecting the River Rhine against pollution, macroinvertebrate biocoenosis on eight locations in the different branches of the Dutch part of the river was analyzed in 0. The results of the investigation have been summarized in this report. On each location two habitats were sampled: stones in the littoral zone at the end of the groynes on the right and left bank, and the river bottom at the deepest part of the river canal. In the first mentioned habitat taxa were found, and in the other. On all locations together, different taxa were observed. Immigrant species were dominant in both habitats.

4 INTRODUCTION. After the severe pollution of the River Rhine in November, caused by a fire in one of the factories of the chemical concern Sandoz near Basel, the different countries joined in the International Commission for protecting the River Rhine against pollution (I.R.C.), took the initiative to pay more attention to biological monitoring. Before that time, only the control of chemical compounds in the river water had been emphasized. One of the results of the initiative was an international programme for monitoring fish species, macroinvertebrates, plankton and water plants in the river channel at five years interval, starting in 0 (Anon., ). The intention of this measuring programme is to get information about the ecological state of the River Rhine. Information, necessary for the ecological rehabilitation programme of this river. Data from previous years concerning the occurrence of macroinvertebrates in the different Rhine branches in The Netherlands are scarce. Preceding the start of the monitoring programme, the locations proposed in The Netherlands were investigated in (Bij de Vaate & Greijdanus-Klaas, ).Klink & Moller-Pillot () published a list of species recently found the River Waal (fig. ), Van den Brink, et al (0) give a survey of species sampled in the cooling-water intake of an electric power plant along the same river near Nijmegen. Others (Van Urk, ; Van den Brink & Van der Velde, a, b;van den Brink et al,, ;Bij de Vaate & Greijdanus-Klaas, 0;Bij de Vaate et al., ) reported about the occurence of single species. Only in the River IJssel (fig. ) relatively more attention has been given to some groups of macroinvertebrates living on stones in the littoral zone during the last years (Van Urk,,,; Van Urk & Bij de Vaate, 0,Bij de Vaate, in press). A survey of changes in the macroinvertebrate community in the Dutch part of the River Rhine during this century was given by Van den Brink e.a. (0). The results of the 0River Rhine macroinvertebrate monitoring programme are summarized in this report.

5 STUDYAREA. Soon after crossing the Dutch-German border near Tolkamer, the Rhine splits up into two branches: the Waal and the Pannerdens Kanaal, going into western and northern direction respectively (Fig. ). East of Dordrecht, the Waal splits up into the Beneden Merwede and the Nieuwe Merwede. The Nieuwe Merwede and Meuse flow together into the Hollandsch Diep. Discharge of both rivers into the North Sea flows bywayof the Haringvliet sluices,which are located in the barrier dam forming the west bank of Lake Haringvliet. The Beneden Merwede is connected with the Oude Maas, and with the man-made canal, the Nieuwe Waterweg. This canal forms the connection between the harbours of Rotterdam and the North Sea. To prevent an extension of the area with brackish ground water around the Oude Maas and the Nieuwe Waterweg, discharge of the Rhine and Meuse is regulated by the Haringvliet sluices. This means maintening a discharge of at least 00 m'.s" byway of the Oude Maas and the Nieuwe Waterweg at sufficient discharge of both rivers. The Haringvliet sluices are closed when the combined discharge of the Meuse and the Rhine branches Nederrijn/Lek and Waal is below 00 nrv. Near Arnhem, the Pannerdens Kanaal splits up into the Nederrijn and the IJssel, going into western and northern direction respectively. Downstream of the town of Wijk bij Duurstede the name of the Nederrijn changes into the Lek. In the Nederrijn three weirs have been constructed for water level regulation, and for the distribution of the Rhine discharge over this river branche and the IJssel. In the Lek and in the downstream part of the Waal and the Meuse, the water level is influenced by tidal movements in the North Sea. Discharge of the IJssel, strongly regulated by the weirs in the Nederrijn, is maintained at a minimum of m.sec _ as long as possible at low discharge of the Rhine. In general the flow canal in the Lower Rhine and its branches is fixed by groynes. Where groynes are absent, the river bank is mostly protected against erosion with stones (Van Urk & Smit, ). Average yearly discharge of the Rhine near Tolkamer (at the Dutch-German border) is about,00 m.sec" x,with an average current velocity of.0 m.sec" ; at minimum and maximum discharge 0. and.0 m.sec" respectively. Average current velocities in the Rhine branches at minimum and maximum discharges are: 0. and.0 m.sec" in the Waal, <0. and. m.sec" in the Nederrijn/Lek, and 0. and. m.sec" in the IJssel. More detailed information about the Rhine branches is given by Van Urk (), Van Urk & Smit () and Anon, (undated).

6 STUDY LOCATIONS. Studylocations (Fig. )havebeen chosen near the permanent fieldstations (Lobith, Kampen and Vuren) alongthe river,or on the basisof prevailing hydrological conditions (upstream/downstream,influence ofweirs,tidal movements, a.o.).an important criterion for the choicewasthe imperative absence of a direct influence of wastewater discharges upstream of the locations.in table, asurveyof the study locationsinthe River Rhine and itsbranchesisgiven. Figure.: The samplinglocations inthe Dutch part of the RiverRhine. / \ A/sse/rneer / Lo: Lobith / Ve: Velp f"^ > Ka: Kampen f \Markermeer Rh: Rhenen / \ J Le: Lekkerkerk 'T^^^ y" / Vu: Vuren / ^%~/ { He: Heinenoord / Amsle «tam ^^C^N NM: NieuweMerwede / ^ / _Utrecht / Arnhem f J»Qn 0*%. Rotterdam J ^ ^ ^ > s ^»r^r've ^_Mfe# \ ^^^L~T\r^ V" J J\ Lelystad X. Kampen c\ ^Nijmegen ^"^.)'" ^ *.».. «. i \ %<>! ' * "". " **.... " ' ƒ \..!'.«\ ^^^ >*i * ^"^V/ X_^l \ " -"* >/ :' \ \ f * \ \ j... «* /\ weir O samplinglocation... '""* *., f/ j \ t^.» * "*Vr^ ** r,f ': '

7 On every study location two habitats have been sampled: * stones in the littoral zone at the end of the groynes on the right and left bank (when groynes were absent, stones in the littoral zone of both river banks); * the river bottom at the deepest part of the river canal. Table.: A survey of the study locations (kmr.: the international accepted indication of river distance, in km). River Location kmr. Rhine Waal Nieuwe Merwede Oude Maas Nederrijn Lek IJssel IJssel Lobith Vuren Heinenoord Rhenen Lekkerkerk Velp Kampen Due to very low discharge of the Rhine during sampling period (October ), the stones around the groynes at the location Lobith were above water level. This was the reason that they could not be sampled. On the right bank of the location Lekkerkerk and on the left bank of the location Kampen, groynes are absent. In that situation, stones in the littoral zone of the river bank have been sampled.

8 METHODS. Samples have been taken in the littoral zone of the groynes (around the head) on the right and left river bank, in the deepest part of the flow canal and on a site in the river located at half the maximum distance between the deepest part of the flow canal and the river bank. To make sure that well colonized stones would be sampled, the sampling period chosen was in autumn, the period with the yearly minimum waterievel in the river. At the locations influenced by tidal movements in the North Sea (Lekkerkerk, Nieuwe Merwede and Heinenoord), sampling took place during low tide for the same reason. The sampling program was carried out between October and,0. In the littoral zone of the river bank or the groynes only the macroinvertebrates on stones have been sampled. On the right and left bank, five overgrown stones were brushed in a plastic tray to remove the macroinvertebrates. Zebra mussels were cut from the stones. The macroinvertebrates were then cleaned bywashing them on a 0. mm mesh width sieve before conservation in ethanol %.After cleaning the surface area of the stones was measured. The river bottom was sampled with a hydraulic Van Veen grab. Sampling surface of this grab is 0cm. Five bottom samples were taken on every location. The samples were washed on a 0. mm mesh width sieve and the residue conserved in ethanol %.When bottom samples consisted of coarse sand, or coarse sand mixed with gravel, the macroinvertebrates were washed out by repeatedly mixing small parts of the sample thoroughly with water and decanting the supernatant over the sieve, until the animals had been collected from the entire sample. Bigger particles (pebbles and cobbles) were brushed; the macroinvertebrates brushed off were handled as described above for the sampling of stones. To convert the numbers of animals observed on the stones in the littoral zone to densities per m river bank surface, the following conversion factor was used: N = Sd * (0,000 / sa). In this factor is: N = number of animals m, Sd = sum of animals on n stones, Sa = sum of the mean surfaces (cm ) of the two largest sides of n stones. The presence of taxa in the habitats sampled is expressed in a value that indicates the chance of being found (abbreviated as c.f.-value). When an organism occured in -0% of the samples this value is. At -0%, - 0%, -0% and -00%, the c.f.-value is,, and respectively.

9 RESULTS. Stones in the littoral zone of the groynes and riverbanks. Numbers of animals found on the stones in the littoral zones of the groynes and the river banks (Lekkerkerk, right bank, and Kampen, left bank) are summarized in appendix. From the point of view of richness of species, density in which the single species occur is unimportant. Only the presence of species is the determining factor. Presence of taxa at the different locations, expressed in c.f.-values, has been calculated for the stones of both river banks together. The results are given in table. Table.: The presence of taxa on the the stones in the littoral zone of the groynes or river banks, expressed in c.f.-values. Vur. = Vuren,NM. = NieuweMerwede, Hei. =Heinenoord,Rhe. =Rhenen, Lek. =LekkerkerkandKam. =Kampen. Tricladida Dendrocoelum lacteum Dugesia lugubris D. tigrina D. polychroa Oligochaeta Tubificidae hair Tubificidae - hair Limnodrilus claparedeianus Peloscolex ferox Psammoryctides barbatus Oligochaeta spec. Naididae indet. Nematoda indet. Enchytraeidae indet. Hirudinea Erpobdella octoculata Glossiphonia complanata Helobdella stagnalis Hemiclepsis marginata Piscicola geometra Gastropoda Ancylus fluviatilis Acroloxus lacustris Bithynia tentaculata Ferrisia wautieri Lymnaea peregra f. ovata Physa acuta Vur. NM. Hei. Location Rhe. Lek. Velp Kar

10 Potamopyrgusantipodarum Valvata piscinalis Lamellibranchia Corbicula cf. fluminea Dreissenapolymorpha Pisidiumamnicum P.casertanum P.henslowanum P.moitessierianum P. nitidum P.supinum P.spec. Sphaeriumcorneum Cirripeda Balanusimprovisus Amphipoda Gammaruspulex G. tigrinus G. spec Corophiumcurvispinum C multisetosum C spec Isopoda Isopoda indet. Asellus aquaticus Proaselluscoxalis Trichoptera Trichoptera indet Agraylea multipunctata Ecnomus tenelîus Hydropsychecontubemalis Oecetistestacea Chironomidae Chironomidae indet Tanypodinae Rheopelopiaornata Chironomini Chironomus plumosus C.gr.reductus Cryptochironomus spec. Dicrotendipes gr.nervosus Endochironomusalbipennis Glyptotendipes gr. A Paratendipes spec. Xenochironomusxenolabis Chironomini indet. Tanytarsini Cladotanytarsus gr.mancus Micropsectraatrofasciata Vur. NM. Hei. Location Rhe. Lek. Velp Kar 0

11 Orihocladiinae Cricotopus bicinctus C intersectus C gr. sylvestris C triannulatus C spec Orthocladius spec. Pogonocladius consobrinus Diptera Melanochelia riparia Culicoides indet. Ephemeroptera Caenis horaria Vur. NM. Hei. Location Rhe. Lek. Velp Kam. On all locations or on at least %of all stones examined, the gastropod Bithynia tentaculata, the bivalve Dreissena pofymorpha, the amphipods Gammarus tigrinus and Corophium curvispinum, and larvae of the chironomid taxon Dicrotendipes gr. nervosus have been found. Other species have been found on at least six of the seven sampling locations: the triclads Dugesia lugubris, D. tigrina and D. pofychroa, the gastropods Acroloxus lacustris and Lymnaea peregra f. ovata, the caddis fly Ecnomus tenellus, and the chironomids Cricotopus bicinctus and Gfyptotendipes gr. A. More than %of the the animals found in the habitat 'stones in the littoral zone' belonged to the above mentioned species (Table.). Table. Average density (number per m river bank) of the most important macroinvertebrate taxa on the stones in the littoral zone of the groynes or river banks on the different locations and the contribution of this group of taxa to the biocoenosis (expressed in percentages). Gammarus tigrinus Corophium curvispinum Dreissena polymorpha Bithynia tentaculata Ecnomus tenellus Dicrotendipes gr. nervosus Glyptotendipes gr. A Velp IJssel Kampen Nederrijn/Lek Rhenen Lekkerkerk Waal Vuren Nieuwe Merwede kmr Oude Maas Heinenoord % of the biocoenosis

12 The riverbottom. Texture of the river bottom toplayer was examined by eye. The composition varied from a mixture of gravel and coarse sand at Lobith to a mixture of sand and silt at the locations situated downstream in the different River Rhine branches. Number of animals found in the bottom samples from the deepest part of the river canal are summarized in appendix. The presence of taxa in these samples is given in c.f.-values which are summarized in table. Table.: Presence of taxa in the deepest part of the river canal at the different locations, expressed in c.f.-values. Lob. = Lobith,Vur. = Vuren,NM. = NieuweMerwede,Hei. = Heienoord, Rhe. = Rhenen,Lek. = LekkerkerkandKam. = Kampen. Tricladida Dendrocoelum lacteum Dugesialugubris Dugesiatigrina D.polychroa Oligochaeta Tubificidae hair Tubificidae -hair Limnodrilus claparedeianus L. hoffmeisteri Psammoryctidesbarbatus Naididae indet Nematoda indet. Turbellaria Plagiostonumlemani Hirudinea Erpobdella octoculata Glossiphonia complanata Helobdella stagnalis Piscicolageometra Gastropoda Ancylus fluviatilis Bithynia tentaculata Potamopyrgus antipodarum Valvatapiscinalis Lamellibranchia Corbicula cf. fluminea C.cf. fluminalis Dreissenapolymorpha Pisidiumcasertanum Lob. Vur. NM. Location Hei. Rhe. Lek. Velp Kam.

13 P.henslowanum P. moitessierianum P.nitidum P.subtruncatum P.supinum Sphaeriumcoraeum S. solidum Uniopictorum Amphipoda Gammaruspulex G. tigrinus Corophium curvispinum C. multisetosum Isopoda Asellus aquaticus Proasellus coxalis P.meridianus Trichoptera Ecnomus tenellus Hydropsychecontubernalis Tanypodinae Rheopelopia oraata Chironomini Chironomusgr.reductus C.gr.thummi Cryptochironomus spec. Dicrotendipes gr.nervosus Glyptotendipes gr. A Paratendipes gr.nudisquama Tanytarsini Tvetenia spec. Ephemeroptera Caenis luctuosa Lob. Vur. NM. Location Hei. Rhe. Lek. Velp Kam. The amphipod Gammarus tigrinus and the bivalve Dreissena pofymorpha are the two species which have been found on all locations or in at least %of all bottom samples. On the locations Lobith, Rhenen, Lekkerkerk and Vuren density of the macroinvertebrates in the habitat ^bottom deepest part of the river canal' was relatively low. At Lobith and Velp the amphipods Corophium curvispinum and G tigrinus were the dominant species respectively. The nonindigenous bivalve Corbicula cf. fluminea (Asiatic clam) was the dominant species at Lekkerkerk and Heinenoord. At Kampen and in the Nieuwe Merwede the gastropods Potamopyrgus antipodarum and Valvata piscinalis were the dominant species respectively. Average densities of the most important taxa are given in table. On all locations only - taxa were dominating the biocoenisis (together >% of the biocoenosis).

14 Table. Average densities (number per m ) of the important taxa occurring in the deepest part of the river canal and the contribution of this group to the biocoenosis (expressed in percentages). Oligochaeta Gammarustigrinus Corophiumcurvispinum Dreissenapolymorpha Corbicula cf. fluminea C.cf. fluminalis Pisidium spec Potamopyrgus antipodarum Bithynia tentaculata Valvata piscinalis Hydropsyche contubernalis Rijn Lobith Vèlp IJssel Kampen Nederrijn/Lek Rhenen Lekkerkerk 00 Waal Vuren Nieuwe Merwede kmr Oude Maas Heinenoord % of the biocoenosis

15 DISCUSSION. A complete list of macroinvertebrates, found in the habitats 'stones in the littoral zone' and *bottom deepest part of the river canal' in and 0,is given in appendix. Compared with the sampling programme of, the 0sampling programme was extended with two locations: one location in the Nieuwe Merwede, the other one in the Oude Maas, in the vicinity of Heinenoord. However, in the river bottom at Kampen, and in 0 the stones at Lobith have not been sampled. The 0 sampling programme was executed in about the same period as in : between September and October in,and between October and in 0 (Bij de Vaate & Greijdanus-Klaas, ). In general, the higher numbers of samples taken in 0 must have had a positive effect on the number of taxa found in year, when compared with the results of (Table ). Table.: Number of taxa collected in and in the Dutch part of the River Rhine. Number oftaxa omiegroup Amphipoda Isopoda Tricladida Oligochaeta Hirudinea Gastropoda stones bottom 0 00 stones bottom Lamellibranchia Ephemeroplera Trichoptera Chironomidae othertaxa 0 Total 0 Numberof samples

16 The number of stones sampled in 0increased by %,and the number of taxa found by %. For the bottom samples and both habitats together the number of taxa had increased by % and %respectively in 0,and the number of samples by 0% and % respectively. On the other hand the extension of the 0sampling programme with the sampling sites in the Nieuwe Merwede and in the Oude Maas (location Heinenoord) led to the scoring of typical brackish water species, the fiatworm Plagiostonum lemani, the acorn Balanus improvisus and the amphipod Corophiwn multisetoswn, due to local circumstances. Especially during low river discharge, chloride concentration in the Oude Maas increases regularly as result of tidal movements. On both sampling sites five extra species were observed: the three above mentioned brackish water species, the caddis fly Oecetis testacea, and the bivalve Unio pictorum (Appendix & ). About 0% of the taxa collected in 0 were found in only one of both habitats. However, of these taxa (0% of the total number) were represented with only one specimen (Table ). In general, the taxa found with more than five specimens in one habitat, or occurring on more than one sampling site, are also restricted to that habitat. Table.: A list of taxa only found in one habitat (Locations = thenumberoflocations in whichthetaxonwas found; N = thetotalnumberofspecimensfoundinthesamples). Habitat Locations N stones bottom Plagiostonum lemani Limnodrilus hoffmeisteri Peloscolex ferox Enchytraeidae indet. Hemiclepsis marginata Acroloxus lacustris Ferrisiawautieri Lymnaea peregraf. ovata Physaacuta Corbicula cf. fluminalis Pisidiumamnicum P.subtruncatum Sphaerium solidum Unio pictorum Balanus improvisus 0 Proasellusmeridianus

17 Habitat Locations N stones bottom Agraylea multipunctata Oecetis testacea Chironomus plumosus Endochironomus albipennis Paratendipes gr. nudisquama [Xenochironomus xenolabis Cladotanytarsus gr.mancus Micropsectra atrofasciata Cricotopus bicinctus C. intersectus C. gr. sylvestris C. triannulatus Orthocladius spec. Pogonocladius consobrinus Tvetenia spec. Melanochelia riparia Culicidae indet. Caenis horaria C. luctuosa Striking in the list of macroinvertebrates found in both habitats (Appendix ) in and 0 are the nonindigenous or immigrant species. These macroinvertebrates are supposed to migrate into the River Rhine basin in four different ways: a. in ballast water of ships (intercontinental exchange); b. attached to the outside of a ship's hull; c. actively or passively (e.g.via fishes) in a natural way using the canals built for the interconnection of navigable water systems as a migration route; d. through deliberated introductions by men (e.g. the release of animals out of aquaria). Water quality improvements (Van der Klei et al, ) most probably have effects on the settlement of exotic species in ecosystems under environmental stress like the River Rhine. However, it is difficult to indicate what the key factor is in the survival of these species (Van Urk & Bij de Vaate, 0). An important factor for the settlement success of exotic species is the presence of unoccupied niches. In the River Rhine, these niches have mainly been created by anthropogenic activities. Until the end of the 0's, morphological adaptions and

18 water pollution resulted in the destruction of niches, with led to the extinction of species (Van den Brink et al, 0). Improvement of water quality led to the recovery of former niches. Some of these niches were not occupied by the original species but by immigrants. On the other hand, changes in specific physical and chemical water quality parameters, mainly caused by the discharge of salts by potassium mines, and thermal pollution are considered to be the most important factors for the existance of new niches. Through thermal pollution, water temperature of the River Rhine in The Netherlands increased about C (Geelen et al, ). Natural chloride concentration is estimated to be mg/ (Van der Velde et al, ).Based on samples collected daily, the average chloride concentration was mg/ in the period 0-0,with minimum and maximum concentrations of and 0mg/ respectively (Heymen & Van der Weijden, ). A list of exotic species recently found in the freshwater section of the Dutch part of the River Rhine is given in table 0.Most of these are brackish water species and/or thermophilous, which clearly indicates effects of chloride discharges and thermal pollution on the invertebrate communities (Den Hartog et al, ;Van den Brink et al, 0, ). Table 0: A list of exotic macroinvertebrate species found in the freshwater section of the Lower Rhine. In bold type the species found in or 0 ( C=thermophilousspecies, Cl'=brackishwaterspecies). Species C Cl" Origin Hydrozoa: Craspedacusta sowerbyi Cordylophora caspia Oligochaeta: Branchyura sowerbyi Tricladida: Dugesia tigrina Gastropoda Potamopyrgus antipodarum Lithoglyphus naticoides E. Asia Ponto-Caspian Cosmopolite N. America New Zealand Ponto-Caspian Physa acuta Mediterranean Bivalvia Corbicula cf. fluminea Corbicula cf. fluminalis Dreissena polymorphs Isopoda: Proasellus meridianus Proasellus coxalis Amphipoda: Gammarus tigrinus Gammarus zaddachi Orchestia cavimana Corophium curvispinum E. Asia E. Asia Ponto-Caspian Mediterranean Mediterranean N. America North-Atlantic Ponto-Caspian E. Europe

19 Species C cr Origin Decapoda: Atyaephyra desmaresti Palaemon longirostris Orconectes limosus Astacus leptodactylus Rhithropanopeus harrisii Mediterranean Atlantic-Mediterranean N. America E. Europe N. America Insecta: Eriocheir sinensis Rheocricotopuschalybeatus Nanocladius rectinervis Rheotanytarsus spec. Rheotanytarsus rhenanus E. Asia S. Europe S. Europe Europe, except N. Europe SW. Europe The introduction of G. tigrinus led to the decrease of densities of indigenous amphipod species (Hautus & Pinkster, ) due to its better competitive features (Pinkster, ). Recently, the amphipod Corophium curvispinum invaded the River Rhine (Van den Brink et al,, ). The species builds dense colonies on solid substrates (e.g. location Vuren, Velp and Nieuwe Merwede) which led to a serious competition for space with other lithophilic macroinvertebrates. The reason is that the animals can overgrow the solid substrates with their muddy living tubes. In food-webs however, they can become an important food source for fish species. From view of densities, immigrant species were dominant in the habitats examined in 0. Recent developments in the occurrence of dominant species in the River Rhine can be illustrated by observations in the River IJssel (Bij de Vaate, in press). In table 0dominant and subdominant taxa of macroinvertebrates on stones in the littoral zone in the River IJssel in the period -0 are listed. Taxa were considered to be dominant or subdominant when their contribution was >% or 0-% in the average density of the biocoenosis.

20 Table 0. Dominant (**) and subdominant (*) taxa of macroinvertebrates on stones in the littoral zone in the River Ussel, period -0 (in bold type immigrant species). 0 0 Hirudinae Gammarus tigrinus Asellus aquaticus * ** * ** * ** * * ** * Corophium curvispinum ** Dreissenapotymorpha Chironomidae * * ** ** ** * ** ** ** ** * * Dominant species on the 0 sampling sites, in both habitats examined, were the amphipods G. tigrinus and C. curvispinum, and the bivalve D. potymorpha (zebra mussel). Since its introduction in The Netherlands in the first part of the nineteenth century (Van Benthem Jutting, ), the zebra mussel is a commonly occurring bivalve in the Dutch inland waters. Heavy pollution led to the extinction of this species in the River Rhine branches in the sixties (Wolff, ; Peeters &Wolff, ; Van Urk,, ). Studies in the River IJssel showed that recolonization must have started in due to an improvement of water quality (Van Urk, ; Van Urk & Bij de Vaate, 0). In September densities of zebra mussels (Dreissena potymorpha) on the solid substrate in the littoral zone of the River Rhine branches were assessed at locations. Calculated average densities varied then between 00 and,000 animals per m (Bij de Vaate et al, ). In the amphipod Gammarus tigrinus was found for the first time in the River IJssel (Van Urk & Bij de Vaate 0).First records in The Netherlands date from (Pinkster ). G. tigrinus has relatively high tolerance for polluted water and has a much greater reproductive capacity in oligohaline waters than any of the indigenous gammarid species (Pinkster,Pinkster et al ). First record of the amphipod C. curvispinum in the Rhine, and in The Netherlands, was made in (Van den Brink et al ). The colonization success of this amphipod can be attributed to its tolerance for high salinity (.-.0 mmol Na ) in the Rhine, its breeding behaviour (three generations a year), and to the fact that the animals live in muddy tubes,which provide shelter from predators (Van den Brink et al ). 0

21 LITERATIIRE. Anon.,.Mess-und Untersuchungsprogramm für 0zur Erfassung des Organismen bestandes des Rheins und der Kontamination von Rheinfischen. International Commission on protecting the River Rhine against pollutions (I.R.C.), report nr./. Anon., undated. Le bassin du Rhin / Das Rheingebiet. Commission Internationale de l'hydrologie du Bassin du Rhin / Internationale Kommission für die Hydrologie des Rheingebietes. ISBN Bij de Vaate, A., in press. Long-term changes in the macroinvertebrate fauna of the River Ussel, The Netherlands. Verh. intern. Verein Limnol. Bij de Vaate, A. & M. Greijdanus-Klaas, 0. The Asiatic clam, Corbicula fluminea (Müller, ) (Pelecypoda, Corbiculidae), a new emigrant in the Netherlands. Bull. Zool. Mus. Amsterdam (): -. Bij de Vaate, A. &M. Greijdanus-Klaas,. Monitoring macroinvertebrates in the River Rhine. Results of a study executed in the Dutch part in. RIZA, report -of the project 'Ecological Rehabilitation River Rhine'. Bij de Vaate,A., M. Greijdanus-Klaas & H. Smit,.Densities and biomass of zebra mussels in the Dutch part of the Lower Rhine. In: Neumann, D. & H.A. Jenner (eds.) The zebra mussel, Dreissena pofymorpha. Ecology, biological monitoring and first application in water quality management. Limnologie Aktuell :-. Bij de Vaate, A., A Klink & F. Oosterbroek,. The mayfly, Ephoron virgo (Olivier), back in the Dutch parts of the rivers Rhine and Meuse. Hydrobiol. Bull. ():-0. Den Hartog, C, F.W.B.van den Brink & G. van der Velde,.Brackish-water invaders in the River Rhine. Naturwissenschaften : 0-. Geelen, J.F.M., L.van de Hoogte &M. Veldhoven,. De Rijn. Report Catholic Univ. Nijmegen. Hautus, T. & S. Pinkster,. Range extension in the period -of the alien amphipods, Gammarus tigrinus Sexton,,and Crangonyx pseudogracilis Bousfield,, in The Netherlands (Crustacea, Amphipoda). Bull. Zool. Mus.Amst. ():-. Heymen, R. & M.van der Weijden,. Resultaten van het waterkwaliteitsonderzoek in de Rijn in Nederland. Institute for Inland Water Management & Waste Water Treatment, Lelystad. Report.0, 0 p. Klink, A.G. & H. Moller Pillot,.Onderzoek aan de makro-evertebraten in de grote Nederlandse rivieren.wageningen and Tilburg, report Hydrobiologisch Adviesburo Klink and Oekologisch Advies Bureau Moller Pillot, p. Peeters,J.C.H. &Wolff, W.J.,. Macrobenthos and fishes of the rivers Meuse and Rhine, The Netherlands. Hydrobiol. Bull. : -. Pinkster, S., : The introduction of the alien amphipod Gammarus tigrinus Sexton, (Crustacea, Amphipoda) in The Netherlands ans its competition with indigenous species. Hydrobiol Bull. : -. Pinkster, S., H. Smit & N. Brandse-de Jong, : The introduction of the alien amphipod Gammarus tigrinus Sexton, in The Netherlands ans its competition with indigenous species. Crustaceana Suppl. : -0. Van Benthem Jutting, T.,. Zoet- en brakwatermollusken. In: Redeke, H.C. (ed.), Flora en fauna van de Zuiderzee, monografie van een brakwatergebied: -0. Uitgave Ned. Dierk. Ver., printed by De Boer, Den Helder. Van den Brink, F.W.B. & G. van der Velde, a. Observations on the seasonal and yearly occurrence and the distribution of Atyaephyra desmaresti (Millet, ) (Crustacea, Decapoda, Natantia) in The Netherlands. Hydrobiol. Bull. :-.

22 Van den Brink, F.W.B. & G. van der Velde, b.observations on the population dynamics and distribution of the White Prawn Palaemon longjrostris H. Milne Edwards, (Crustacea, Decapoda, Natantia) in The Netherlands, with special reference to its occurrence in the major rivers. Arch. Hydrobiol. 0: -. Van den Brink, F.W.B., G.van der Velde &J.F.M. Geelen,.Life history parameters and temperature related activity of an American crayfish, Orconectes limosus (Rafinesque, ) (Crustacea, Decapoda), in the area of the major rivers in The Netherlands. Arch. Hydrobiol. : -. Van den Brink, F.B.W., G. van der Velde & A. bij de Vaate,, A note on the immigration of Corophium curvispinum Sars, (Crustacea: Amphipoda) into the Netherlands via the river Rhine. Bull. Zool. Mus.Amsterdam (): -. Van den Brink, F.W.B., G. van der Velde & W.G. Cazemier, 0. The faunistic composition of the freshwater section of the river Rhine in The Netherlands: present state and changes since 00. In: Kinzelbach, R. & G. Friedrich (eds.),biologie des Rheins (Limnol. Aktuell, Vol. ), G. Fischer Verlag, Stuttgart, :-. Van den Brink, F.W.B., G. van der Velde &A. bij de Vaate,. Amphipod invasion on the Rhine. Nature :. Van der Klei,W., R.H. Dekker, H. Kersten & JAW. de Wit,. Water management of the River Rhine: past, present and future. J. Europ. Water Poll. Contr. :-. Van der Velde, G., G.van Urk, F.W.B,van den Brink, F. Colijn, W.A.Bruggeman & R.S.E.W. Leuven,. Rein water, een sleutelfactor in chemisch ecosysteemherstel. In: Hekstra, G.P. & F.J.M. van der Linden (eds.), Flora en fauna chemisch onder druk :-. Pudoc, Wageningen. Van Urk, G.,. De driehoeksmossel Dreissena potymorpha in de Rijn. H 0 :-. Van Urk, G.,. The macrobenthos of the River IJssel. Hydrobiol. Bull. ():-. Van Urk, G.,. Veranderingen in de makro-invertebratenfauna van de IJssel. H 0 ():-. Van Urk, G.,.Lower Rhine-Meuse. In: Whitton, B.A. (ed.), Ecology of European rivers. Blackwell Scientific Publications, Oxford, : -. Van Urk, G. & H. Smit,. The Lower Rhine: geomorphological changes. In: Petts, G.E. (ed.), Historical change of large alluvial rivers:western Europe. John Wiley & Sons, Chichester, : - Van Urk, G. &A. bij de Vaate, 0.Ecological studies in the Lower Rhine in The Netherlands. In: Kinzelbach, R. & G. Friedrich (eds.), Biologie des Rheins. Limnologie aktuell :-. Wolff, W.J.. The Mollusca of the estuarine region of the rivers Rhine, Meuse and Scheldt in relation to the hydrgraphy of the area. II. The Dreissenidae. Basteria : -0.

23 Appendix I. Number of animals collected at the locations Vuren, Nieuwe Merwede, Heinenoord, Rhenen, Lekkerkerk, Velp and Kampen from the stones in the littoral zone of the groynes on the right (sample R-R) and left bank (sample L-L) or from the stones in the littoral zone of the river banks when groynes were absent (Lekkerkerk: right bank; Kampen: left bank). The surface given is the mean value (cm ) of the two largest sides of each stone. Vuren Tricladida Dendrocoelum lacteum Dugesia lugubris Dugesia tigrina Dugesia polychroa Oligochaeta Tubificidae hairs Tubificidae -hairs Psammoryctidesbarbatus Hirudinea Erpobdellaoctoculata Glossiphonia complanata Gastropoda Ancylus fluviatilis Acroloxus lacustris Bithynia tentaculata Lymnaea peregraf. ovata Lamellibranchia Dreissena polymorpha Pisidium nitidum Pisidium supinum Sphaerium corneum Amphipoda Gammarus tigrinus Gammarusspec. Corophium curvispinum Isopoda Proasellus coxalis Trichoptera Ecnomustenellus Hydropsychecontubernalis Chironomidae Chironomidae indet. Tanypodinae Rheopelopia oraata Rl 0 R R Samples from the stones R R LI L L 0 0 L 0 L 0

24 Samples from the stones Rl R R R R LI L L L L Chironomini Chironomini indet. Dicrotendipes gr. nervosus Endochironomus albipennis Glyptotendipes gr. A Tanytarsinl Micropsectra atrofasciata Orthocladiinae Cricotopus spec. Cricotopus bicinctus Diptera Melanochelia riparia surface (cm )

25 NieuweMerwede Tricladida Dugesia lugubris Dugesiatigrina Dugesiapolychroa Oligochaeta Tubificidae hairs Tubificidae -hairs Hirudinea Glossiphonia complanata Gastropoda Ancylus fluviatilis Acroloxus lacustris Bithynia tentaculata Lymnaea peregraf. ovata Physa fontinalis Valvata piscinalis Lamellibranchia Dreissenaporymorpha Pisidium moitessierianum Sphaeriumcorneum Amphipoda Gammarus tigrinus Gammarus spec Corophiumcurvispinum Isopoda Asellusaquaticus Isopoda indet. Trichoptera Ecnomustenellus Oecetis testacea Chironomidae Chironomidae indet. Tanypodinae Rheopelopia ornata Chironomini Cryptochironomus spec. Chironomus gr.reductus Dicrotendipes gr.nervosus Glyptotendipes gr. A Paratendipes spec Orthocladiinae Cricotopus bicinctus Cricotopus triannulatus Orthocladius spec Pogonocladius consobrinus RI R R Samples from the stones R R LI L L 0 L L surface (cm )

26 Heinenoord Tricladida Dugesia tigrina Dugesia polychroa Hirudinea Piscicola geometra Gastropoda Ancylus fluviatilis Acroloxuslacustris Bithyniatentaculata Lymnaea peregraf. ovata Physa acuta Valvata piscinalis Lamellibranchia Corbicula cf. fluminea Dreissena polymorpha Cirripedia Balanus improvisus Amphipoda Gammarus tigrinus Gammarus spec. Corophium curvispinum Corophium multisetosum Corophium spec. Trichoptera Ecnomus tenellus Chironomidae Chironomidae indet. Chironomini Dicrotendipes gr. nervosus Glyptotendipes gr. A Orthocladiinae Cricotopus bicinctus Ceratopogonidae Culicoides indet. Rl R R Samples from the stones R R LI L L L L surface (cm )

27 Rhenen Tricladida Dendrocoelum lacteum Dugesia lugubris Gastropoda Acroloxuslacustris Bithyniatentaculata Ferrisiawautieri Lymnaea peregraf. ovata Lamellibrancbia Dreissena pofymorpha Amphipoda Gammaruspulex Gammarustigrinus Gammarus spec Corophium curvispinum Isopoda Asellus aquaticus Trichoptera Fxnomus tenellus Chironomidac Chironomidae indet. Chironomini Dicrotendipes gr.nervosus Endochironomus albipennis Glyptotendipes gr. A Xenochironomusxenolabis Tanytarsinl Cladotanytarsus gr.mancus Orthocladiinae Cricotopus spec Cricotopus bicinctus Cricotopus intersectus Cricotopus gr.sylvestris Diptera Melanochelia riparia Rl 0 R 0 0 R Samples from thestones R R LI L L 0 L 0 L 0 surface (cm )

28 Lekkerkerk Tricladida Dendrocoelum lacteum Dugesia lugubris Dugesia tigrina Dugesia polychroa Oligochaeta Tubifîcidae hairs Tubificidae - hairs Psammoryctides barbatus Oligochaeta indet. Naididae indet Nematoda indet. Enchytraedidae indet. Hirudinea Erpobdella octoculata Gastropoda Ancylus fluviatilis Acroloxus lacustris Bithynia tentaculata Lymnaea peregra f. ovata Potamopyrgus antipodarum Valvata piscinalis Lamellibranchia Corbicula cf. fluminea Dreissena polymorpha Pisidium moitessierianum Amphipoda Gammarus pulex Gammarus tigrinus Gammarus spec. Corophium curvispinum Corophium multisetosum Corophium spec. Isopoda Asellus aquaticus Trichoptera Ecnomus tenellus Chironomidae Chironomidae indet. Chironomini Chironomus plumosus Dicrotendipes gr. nervosus Endochironomus albipennis Glyptotendipes gr. A Xenochironomus xenolabis Rl R 0 0 R 0 0 Samples from the stones R R LI L L L L surface (cm )

29 Velp Tricladida Dugesialugubris Dugesia tigrina Dugesia polychroa Oligochaeta Psammoryctidesbarbatus Hirudinea Erpobdella octoculata Glossiphoniacomplanata Gastropoda Acroloxus lacustris Bithyniatentaculata Ferrisiawautieri Lymnaea peregraf. ovata Lamellibranchia Dreissenapolymorpha Pisidiumamnicum Pisidiumcasertanum Pisidiumhenslowanum Pisidium nitidum Sphaeriumcorneum Amphipoda Gammarustigrinus Gammarus spec Corophiumcurvispinum Isopoda Isopoda indet Trichoptera Ecnomus tenellus Hydropsychecontubernalis Chironomidae Chironomidaeindet. Tanypodinae Rheopelopia ornata Chironomini Dicrotendipes gr.nervosus Glyptotendipes gr. A Xenochironomus xenolabis Orthocladiinae Cricotopus spec Cricotopus bicinctus Cricotopus gr.sylvestris surface (cm ) Samples from the stones Rl R R R R LI L L 0 L L

30 Kampen Tricladida Dendrocoelum lacteum Dugesia lugubris Dugesia tigrina Dugesia polychroa Oiigochaeta Tubificidae hairs Tubificidae - hairs Limnodrilus claparedeianus Peloscolex ferox Psammoryctides barbatus Oiigochaeta indet. Hirudinea Erpobdella octoculata Glossiphonia complanata Helobdella stagnalis Hemiclepsis marginata Gastropoda Acroloxus lacustris Bithynia tentaculata Lymnaea peregra f. ovata Potamopyrgus antipodarum Valvata piscinalis Lamellibranchia Dreissena polymorphs Pisidium casertanum Pisidium henslowanum Pisidium moitessierianum Pisidium nitidum Pisidium spec. Sphaerium corneum Amphipoda Gammarus pulex Gammarus tigrinus Gammarus spec Corophium curvispinum Corophium spec. Isopoda Isopoda indet. Asellus aquaticus Proasellus coxalis Trichoptera Trichoptera spec. Agraylea multipunctata Ecnomus tenellus Chironomidae Chironomidae indet. Chironomini Dicrotendipes gr. nervosus Glyptotendipes gr. A Xenochironomus xenolabis Rl 0 0 R 0 R Sampl es from the stones R R LI L L L L 0 0 0

31 Tanytarsini Cladotanytarsus gr. mancus Orthocladiinae Cricotopus bicinctus Cricotopus gr. sylvestris Diptera Melanochelia riparia Ephemeroptera Caenis horaria Rl R R Samples from the stones R R LI L L L L surface (cm )

32 Appendix. Number of animals collected in the bottom samples (-) from the deepest part of the river canal at the locations Lobith, Vuren, Nieuwe Merwede Heinenoord, Rhenen, Lekkerkerk, Velp and Kampen. Lobith Tricladida Dugesia tigrina Oligochaeta Tubificidae hairs Tubificidae - hairs Psammoryctides barbatus Gastropoda Bithynia tentaculata Lamellibranchia Corbicula cf. fluminalis Dreissena polymorpha Pisidium henslowanum Pisidium supinum Sphaerium corneum A MIMMlUlila Ainpiupoaa Gammarus tigrinus Gammarus spec. Corophium curvispinum Trichoptera Hydropsyche contubernalis Chironomidae Dicrotendipes gr. nervosus Orthocladiinae Tvetenia spec Bottom sample

33 Vuren Oligochaeta Tubificidae -hairs Hirudinea Piscicolageometra Gastropoda Ancylus fluviatilis Bithyniatentaculata Potamopyrgusantipodarum Valvata piscinalis Lamellibranchia Corbiculaaf. fluminalis Dreissenapoh/morpha Pisidium henslowanum Pisidium moitessierianum Pisidium subtruncatum Sphaerium corneum Amphipoda Gammarus tigrinus Gammarus spec Corophium curvispinum Corophiumspec. Trichoptera Ecnomus tenellus Chironomidae Chironomidae indet. Chironomini Chironomus gr.reductus Cryptochironomusspec. Dicrotendipes gr.nervosus Glyptotendipes gr. A Bottom sample

34 NieuweMerwede Tricladida Dugesia lugubris Oligochaeta Tubificidae - hairs Turbellaria Plagiostonum lemani Gastropoda Potamopyrgus antipodarum Valvata piscinalis Bivalvia Corbicula cf. fluminalis Dreissena polymorpha Pisidium casertanum Pisidium henslowanum Pisidium moitessierianum Pisidium nitidium Pisidium subtruncatum Pisidium supinum Sphaerium solidum 0 Bottom sample Ampnipoaa Gammarus tigrinus Gammarus spec. Corophium curvispinum Trichoptera Hydropsyche contubernalis Chironomini Chironomus gr. reductus Cryptochironomus spec.

35 Heinenoord Oligochaeta Tubificidae hairs Tubificidae -hairs Hirudinea Erpobdellaoctoculata Glossiphonia complanata Gastropoda Bithynia tentaculata Potamopyrgusantipodarum Valvata pisdnalis Corbicula af. fluminea Dreissenapolymorpha Pisidiumcasertanum Pisidiumhenslowanum Pisidiummoitessierianum Pisidiumnitidum Pisidiumsubtruncatum Pisidiumsupinum Pisidiumspec. Sphaerium corneum Unio pictorum Amphipoda Gammarustigrinus Gammarus spec Corophiumcurvispinum Corophium multisetosum Corophium spec Isopoda Isopoda indet Chironomidae Chironomidae indet. Chironomini Cryptochironomus spec Glyptotendipes gr. A ] Bottomsampl e

36 Rhenen Tricladida Dugesia polychroa Oligochaeta Tubificidae hairs Tubificidae - hairs Hirudinea Erpobdella octoculata Helobdella stagnalis Piscicola geometra Gastropoda Bithynia tentaculata Potamopyrgus antipodarum LameUibranchia Dreissena polymorpha Pisidium casertanum Pisidium henslowanum Amphipoda Gammarus tigrinus Gammarus spec. Corophium curvispinum Tanypodinae Rheopelopia ornata Chironomini Chironomus gr. reductus Cryptochironomus spec. Bottom sample k Lekkerkerk Gastropoda Bithynia tentaculata Potamopyrgus antipodarum LameUibranchia Corbicula cf. fluminea Dreissena polymorpha Amphipoda Gammarus tigrinus Gammarus spec. Corophium spec. Bottom sample 0 0

37 Velp Tricladida Dendrocoelumlacteum Dugesia lugubris Dugesia polychroa Oligochaeta Peloscolex ferox Tubificidae hairs Tubificidae hairs Hirudinea Erpobdella octoculata Glossiphonia complanata Helobdellastagnalis Gastropoda Bithynia tentaculata Potamopyrgusantipodarum Lamellibranchia Gorbiculaaf. fluminalis Dreissena polymorpha Pisidium henslowanum Pisidium nitidum Pisidiumsubtruncatum Sphaeriumcorneum Amphipoda Gammarustigrinus Gammarus spec Corophiumcurvispinum Isopoda Asellus aquaticus Proasellus coxalis Proasellusmeridianus Trichoptera Hydropsyche contubernalis Chironomini Dicrotendipes gr.nervosus Ephemeroptera Caenis luctuosa Bottomsample

38 Kampen OUgocbaeta Tubificidae hairs Tubificidae - hairs Limnodrilus claparedeianus Limnodrilus hoffmeisteri Psammoryctides barbatus Naididae indet Nematoda indet Gastropoda Bithynia tentaculata Potamopyrgus antipodarum Dreissena polymorpha Pisidium casertanum Pisidium henslowanum Pisidium moitessierianum Pisidium subtruncatum Amphipoda Gammarus pulex Gammarus tigrinus Gammarus spec. Trichoptera Hydropsyche contubernalis Chironomidae Chironomidae indet. Chironomini Chironomus gr. reductus Cryptochironomus spec. Paratendipes gr. nudisquama 0 0 Bottom sample

39 Appendix. The taxa observed in the two examined habitats in the River Rhine and its branches. (S = stones in the littoral zone of the groynes or river banks, B = bottom in the deepest part of the river canal, and 0 = and 0 respectively). Tricladida Dendrocoelum lacteum Dugesia lugubris D. tigrina D. polychroa Turbellaria Plagiostonum lemani Oligochaeta Tubificidae hairs Tubificidae - hairs Limnodrilus claparedeianus L. hoffmeistri Peloscolex ferox Psammoryctides barbatus Naididae indet. Enchytraeidae indet. Hirudinea Erpobdella octoculata E. testacea Glossiphonia complanata G. heteroclita Helobdella stagnalis Hemiclepsis marginata Piscicola geometra Gastropoda Ancylus fluviatilis Acroloxus lacustris Bithynia leachi B. tentaculata Ferrisia wautieri Gyraulus albus Lymnaea peregra f. ovata Physa acuta P. fontinalis Potamopyrgus antipodarum Valvata piscinalis Lamellibranchia Corbicula cf. fiuminea C. cf. fiuminalis Dreissena polymorpha Pisidium amnicum P. casertanum P. henslowanum P. moitessierianum $ Habitat Sço Bœ B«o

40 P. nitidum P. subtruncatum P. supinum Sphaerium coraeum S.solidum Unio pictorum Cirripeda Balanusimprovisus Amphipoda Gammarus pulex G. tigrinus Corophium curvispinum C. multisetosum Isopoda Asellus aquaticus Proasellus coxalis P. meridianus Tricboptera Agraylea multipunctata Ecnomus tenellus Hydropsyche contubernalis Oecetis testacea Tanypodinae cf. Conchapelopia spec. Procladius spec. Rheopelopia ornata Chironomini Cbironomus plumosus C.gr. fluviatilis C. gr. reductus C gr. thummi Cryptochironomus spec. Dicrotendipes gr. nervosus Endochironomus albipennis Glyptotendipes gr. A Parachironomus gr.longiforceps Paratendipes gr. nudisquama Polypedilum gr. breviantennatum Xenochironomus xenolabis Tanytarsini Cladotanytarsus gr.mancus Micropsectra atrofasciata Rheotanytartus rhenanus Orthocladiinae Cardiocladius spec. Cricotopus bicinctus C. intersectus C. gr. sylvestris C. triannulatus Eukiefferiella discoloripes Nanocladius bicolor Orthocladius spec. Paratrichocladius rufiventris Pogonocladius consobrinus Habitat S» ^*> " B» 0

41 Rheocricotopus chalybeatus Tvetenia spec. Diptera Melanochelia riparia Tipulidae indet. Culicidae Culicidae indet. Ephemeroptera Caenis horaria C. luctuosa $ Habitat S» Bœ B*

42 Appendix. The taxa observed in 0 in the habitat 'stones in the littoral zone' in the River Rhine and its branches (Vu = Vuren,NM = NieuweMerwede,He = Heienoord,Rh = Rhenen, Le = LekkerkerkandKa = Kampen). Trkladida Dendrocoelum lacteum Dugesia lugubris D. tigrina D. polychroa Oligochaeta Tubificidae hairs Tubificidae - hairs Limnodrilus claparedeianus Peloscolex ferox Psammoryctides barbatus Naididae indet. Enchytraeidae indet. Hirudinea Erpobdella octoculata Glossiphonia complanata Helobdella stagnalis Hemiclepsis marginata Piscicola geometra Gastropoda Ancylus fluviatilis Acroloxus lacustris B. tentaculata Ferrisia wautieri Lymnaea peregra f. ovata Physa acuta P. fontinalis Potamopyrgus antipodarum Valvata piscinalis Lamellibranchia Corbicula cf. fluminea Dreissena polymorpha Pisidium amnicum P. casertanum P. henslowanum P. moitessierianum P. nitidum P. supinum Sphaerium corneum Cirripeda Balanus improvisus Amphipoda Gammarus pulex Vu NM He Location Rh Le Ve Ka

43 G. tigririus Corophium curvispinum C multisetosum Isopoda Asellus aquaticus Proascllus coxalis Trichoptera Agraylea multipunctata Ecnomus tenellus Hydropsychecontubernalis Oecetis testacea Tanypodinae Rheopelopia ornata Chironomini Chironomus plumosus C gr. reductus Cryptochironomus spec. Dicrotendipes gr. nervosus Endochironomus albipennis Glyptotendipes gr. A Xenochironomus xenolabis Tanytarsini Qadotanytarsus gr. mancus Micropsectra atrofasciata Ortbocladiinae Criootopus bicinctus C intersectus C gr. sylvestris C triannulatus Orthocladius spec. Pogonocladius consobrinus Diptera Melanochelia riparia Culiddae Culicidae indet. Ephemeroptera Caenis horaria Vu NM He Location Rh Le Ve Ka

44 Appendix. The taxa observed in 0 in the habitat Txrttom in the deepest part of the river canal' in the River Rhine and its branches (Lo =Lobith,Vu = Vuren,NM =Nieuwe Merwede,He = Heienoord,Rh = Rhenen,Le = LekkerkerkandKa =Kampen). Tricladida Dendrocoelum lacteum Dugesia lugubris D. tigrina D. polychroa Turbellaria Plagiostonum lemani Oligochaeta Tubificidae hairs Tubificidae - hairs Limnodrilus claparedeianus L. hoffmeisteri Peloscolex ferox Psammoryctides barbatus Naididae indet. Hirudinea Erpobdella octoculata Glossiphonia complanata Helobdella stagnalis Piscicola geometra Gastropoda Ancylus fluviatilis B. tentaculata Potamopyrgus antipodarum Valvata piscinalis Lamellibranchia Corbicula cf. fluminea C. cf. fluminalis Dreissena polymorphs Pisidium casertanum P. henslowanum P. moitessierianum P. nitidum P. subtruncatum P. supinum Sphaerium corneum S. solidum Unio pictorum Amphipoda Gammarus pulex G. tigrinus Corophium curvispinum C. multisetosum Lo Vu NM Location He Rh Le Ve Ka

45 Location Lo Vu NM He Rh Le Ve Ka Isopoda Asellus aquaticus Proasellus coxalis P. meridianus Trichoptera Ecnomus tenellus Hydropsyche contubernalis Oecetis testacea Tanypodinae Rheopelopia ornata Chironomini C. gr. reductus Cryptochironomus spec. Dicrotendipes gr. nervosus Glyptotendipes gr. A Paratendipes gr. nudisquama Orthocladiinae Tvetenia spec.

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