Environmental Variables Influencing the Distribution of Hydraenidae and Elmidae Assemblages (Coleóptera) in a Moderately-Polluted River Basin in North-Western Spain

Eur. J. Entomol. 96:37—44, 1999 ISSN 1210-5759

Environmental variables influencing the distribution of Hydraenidae and Elmidae assemblages (Coleóptera) in a moderately-polluted river basin in north-western Spain

F rancisco GARCÍA-CRIADO1, C am ino FERNÁNDEZ-ALÁEZ2 and M argarita FERNÁNDEZ-ALÁEZ2

'Departamento de Biología Animal, Facultad de Biología, Universidad de León, 24071 León, Spain; e-mail: [email protected] 2Área de Ecología, Facultad de Biología, Universidad de León, 24071 León, Spain

Key words. Coleóptera, water beetle assemblages, Hydraenidae, Elmidae, environmental factors, pollution indicators, TW1NSPAN, CCA

Abstract. The Hydraenidae and Elmidae assemblages living in the Órbigo River Basin (NW Spain) were studied during one year. The aim of the research was to determine which factors were best related to species composition. This knowledge is the first step to wards the definition o f indicator species or assemblages. Canonical Correspondence Analysis (CCA) showed that altitudinal gradient was the factor most correlated with beetle distribution. However, some other variables, such as water mineralization and eutrophication, were also important. Using TWINSPAN program, groups o f sites were defined and, afterwards, represented on the CCA diagram. Several species as semblages were defined on the basis o f their frequencies o f occurrence in these site groups. The environmental features o f site groups and beetle assemblages were assessed with the aid o f CCA. In this way, assemblages typical o f high reaches could be sepa rated from those of low stretches o f the rivers. Similarly, communities from non-polluted waters could also be defined. Although several species are present in polluted sites, no assemblage exclusive to these sites has been found.

INTRODUCTION The question arose of which factors were more related to Faunistic and taxonomic studies on Hydraenidae and the community composition. So, in this paper we have Elmidae have become increasingly important in Spain in taken a more global approach, at an assemblage level, in recent years (Montes & Soler, 1986; Valladares & Mon volving numerous environmental variables. tes, 1991; Rico, 1996). The degree of knowledge about MATERIAL AND METHODS these subjects is relatively high in some regions, includ Detailed information on the characteristics o f the Orbigo ing the north-western area of the country (Valladares, River basin is given in García Criado & Fernández Aláez 1988, 1989; Garrido, 1990; Díaz Pazos, 1991). It would (1994). This basin lies mainly on a siliceous substratum with be expedient to go deep into other aspects related to the only the northern rivers (Luna and Torrestio) flowing over cal ecology of these species. This is the previous step to the careous areas. There are no important pollution sources. How assessment of the suitability of these families as pollution ever, a moderate level o f urban and agriculture-derived contami indicators. nation is apparent in the lowest reaches o f the Orbigo and The relatively small amount of work carried out in this Tuerto Rivers. The result is a moderate eutrophication by inor field in Spain so far has usually focused on autecological ganic nutrients. considerations (Puig, 1983; Sáinz-Cantero et al., 1987). Thirty seven sites were sampled in each season o f one year, in However, the study of communities as a whole has con April, July/August, October and February (Fig. 1). Each sample comprised a search o f five minutes in the centre o f the river. siderable advantages over individual species analysis. The samples were always taken on stony substratum devoid of This fact has been taken into account by several authors, vegetation. The substratum consisted o f cobbles in all the sam who have made use of classification and ordination tech plings, with occasional larger rocks (up to 40 cm) at some head niques applied to the study of both macrobenthic (Wright water sites. No specimens were collected in three locations (L-l, et al., 1984; Rutt et al., 1989; Monzón et al., 1990; Jef Tu-2 and Or-7), so it has not been possible to include them in fries, 1994; Malmqvist & Maki, 1994; Petts & Bickerton, the subsequent analysis. Physical and chemical measurements 1994; Armitage et al., 1995; Collinson et al., 1995; Ver- were averaged over the four visits to each site. Similarly, spe donschot, 1995) and Coleóptera assemblages (Soler et al., cies data were taken altogether regardless o f the season. In this 1976; Eyre et al., 1986, 1993; Foster et al., 1992; Ribera way, a large enough number o f species and individuals is avail able to effect a representative multivariate approach (Millet & & Foster, 1992). Prat, 1984). Qualitative data were used for the multivariate In previous papers, we have offered some autecological analysis. data from research carried out in the Orbigo River Basin, Canonical Correspondence Analysis, CCA (Ter Braak, 1986), aiming to describe the ecological preferences of some has been used to process the information. It is an ordination species of Hydraenidae and Elmidae (García Criado et al., technique allowing the relationship o f a set o f variables with the 1994, 1995; García Criado & Fernández Aláez, 1995). distribution o f a community to be examined. Twenty-two physi-

37 istence of siliceous and calcareous areas is shown by the wide range of conductivity and silicate.

Table 1. Range of environmental data measured during the study period. It illustrates the general characteristics of the ba sin.

Range pH 6.5-9.7 Conductivity (gS/cm) 17-294 Oxygen (mg/1) 7-15.2 Nitrate (mg/1 N-NOj") 0-6.89 Total phosphorus (pM POA) 0.11-3.95 Silicate (mg/1 Si) 0.35-10.3 Sulphate (mg/1 S 0 42“) 2-34.7 Chloride (mg/1) 0.48-23.2 Altitude (m) 720-1,360

The eigenvalues for CCA axes 1-4 were 0.553, 0.368, 0.202 and 0.137. Correlations of axes 3 and 4 with envi ronmental variables were low (r < 0.5), and only axes 1 and 2 were used for data interpretation. The cumulative percentage of variance of species-environment relation is 58.1 for these two axes (see Table 2 for further informa tion). The first canonical axis was significant as shown by Monte Carlo permutation test (p = 0.01). The overall Monte Carlo test also gave a significance of p = 0.01.

Table 2. Eigenvalues and cumulative percentage variance for CCA axes.

Axes 1 2 3 4 Eigenvalues 0.553 0.368 0.202 0.137 Fig. 1. Geographical situation o f the study area, showing the Cumulative percentage variance sampling sites. o f species data 14.6 24.4 29.7 33.3 o f species-environment relation 34.9 58.1 70.8 79.5 cal and chemical parameters were measured in the streams: wa ter temperature, pH, conductivity, total suspended solids, oxy In order to get the most from the CCA plot (Fig. 2), we gen concentration and saturation, alkalinity, chemical oxygen must take into account, as Ter Braak (1987) states, that demand, biochemical oxygen demand, calcium, magnesium, so every arrow representing each one of the variables deter dium, potasium, ammonium, nitrite, nitrate, ortophosphate, total mines a direction or “axis” in the diagram; the species dissolved phosphorus, total phosphorus, sulphates, chlorides and silicates. Altitude and distance from the source were also in points can be projected on to this axis, indicating aproxi- cluded. Gradient, depth, current velocity and flow are closely mately its position along an environmental variable. For related to altitude (and distance from the source) in the study example, Esolus pygmaeus is found in sites showing a area and have not been considered. Variables giving more re high concentration of chloride, while, at the other end of dundant information (variance inflation factor above 20 in the graph, Ochthebius heydeni, Hydraena inapicipalpis, CCA) were removed in order to make interpretation easier; in and Oulimnius tuberculatus, for example, occur in sites this way statistical problems were also avoided. The parameters with low concentrations. The arrow points in the direction finally selected were altitude, pH, conductivity, nitrate, of maximum change of the variable across the diagram, sulphate, total phosphorus, chloride, oxygen and silicate. Their while its length is proportional to the rate of change (Ter variance inflation factor was below 7, indicating that they were not significantly autocorrelated. Braak, 1987). The longer the arrow, the stronger the cor Secondly, classification o f sites was carried out by means o f relation with the ordination axes. Two Way Indicator Species Analysis, TWINSPAN (Hill, 1979), The first axis is most correlated with altitude. a program producing a hierarchical, divisive classification. Therefore, longitudinal gradient-derived variations seem to be the main factor in Hydraenidae and Elmidae distri RESULTS bution. Species (Fig. 2) and sites (Fig. 3) from high 3,973 adults belonging to 32 species of Hydraenidae reaches are located on the negative side of this axis, while and Elmidae were collected. The ranges of the nine envi those from low reaches are found at the positive end. ronmental variables appear in Table 1. A moderate Axis 2 is partially related to alkaline mineralization of eutrophication is revealed by these data. Similarly, the ex- the water (conductivity, pH). This situation is a natural consequence of the lithological characteristics of the ba-

38 Il

Fig. 2. CCA ordination diagram (axes I and II). The arrangement o f species in relation to the environmental variables (arrows) shows their ecological preferences. sin, with a marked contrast between siliceous and calcare on the CCA diagram (Fig. 3) has allowed us, firstly, to ous areas. Sites with the highest level of mineralization confirm that the elements inside each group are related are on the positive end of this axis, as well as the species (appear next to each other in the plot) and, secondly, to collected from these sites. This axis is also related to define their environmental attributes. The ecological fea eutrophication, as shown mainly by the concentrations of tures of the TWINSPAN groups are summarized in Table nitrate and phosphorus. Concentration of chloride is also 3 by the averages of environmental variables. an indication of this pollution. The characteristics of the TWINSPAN groups obtained TWINSPAN program provided seven groups of sites were as follows: after three divisions (Fig. 4). The display of these groups

Tabu - 3. Average values o f the environmental variables for the seven TWINSPAN groups. Or- 3 and Tr-1 have been excluded.

A B C D E F G PH 8.20 7.78 7.68 8.14 7.35 8.17 7.68 Conductivity (pS/cm) 204.33 39.70 56.50 160.89 31.69 173.92 59.43 Oxygen (mg/1) 11.29 12.16 11.25 11.84 11.07 11.54 11.67 Nitrate (mg/1 N-NCV) 1.77 0.84 1.35 1.07 0.44 1.56 0.99 Total phosphorus (pM P O f) 2.04 0.22 0.73 0.82 0.52 0.77 0.67 Silicate (mg/1 Si) 1.75 2.56 4.11 2.83 4.20 3.26 5.14 Sulphate (mg/1 SO f) 15.88 3.47 3.84 6.65 2.95 5.33 3.35 Chloride (mg/1) 9.79 2.74 3.70 3.54 1.55 1.45 0.91 Altitude (m) 747 760 845 906 980 1,205 1,300

39 Il A

'Tu5.°^.Or8;

I • Toi 2 F

To2 L2 \ * Om2', O r5*\ !• L3 L5 0/6 L4* D OrV Tr2 Or2 /• Or3 GA Om1' '•Om3 (Va Tri- C / 1- • ■*_ ■i------1 I Om4 2 3 -3 -2 Tu4/'T*3V" N Or1. B Du1 E, E1. H\ \ I “1 • «Du2 E2_E3 -

-2

Fig. 3. CCA ordination diagram (axes I and II) with sites. TWINSPAN groups are represented with broken lines. Or-3 has not been included within group A for greater clarity. See Fig. 2 for the positions o f the environmental variables.

A. When comparing physical, chemical and faunistic diagram and the intermediate values of phosphorus, sul data, Or-3 is found to be misclassifted. On removing it, a phate and chloride (Table 3). sharply defined group is obtained. It comprises the lowest E. A well-defined group of sites characterized by little and most strongly-polluted locations in the basin. Since mineralization. The siliceous nature of the substratum current velocity, altitude, substratum and other character causes the conductivity to be low and the silicate concen istics of the river are similar to those found in other sites, tration to be relatively high. They are all medium altitude pollution seems to be the main factor causing the separa points, although some of them are located near the source. tion of this group. The CCA plot shows that these sites The level of pollution is low, as shown by phosphorus, are positively correlated with phosphorus and chloride sulphate and chloride concentrations (Table 3). concentrations, and negatively with altitude. Total phos F. Sites from headwaters with some of the highest alti phorus, sulphate and chloride values are the highest in the tudes in the study area. Pollution levels are low. Nitrate study area and include the maxima found in the basin. concentration is somewhat high, but it seems of little im The average values for the whole group are consistently portance in comparison with other parameters. Water high for these variables (Table 3). mineralization is high due to the calcareous substratum, B. The fact of comprising just one site with similar except for Om-2, which is located on siliceous characteristics to those in group C does not make possible substratum. a satisfactory interpretation of this group. Therefore, it G. Unpolluted sites from siliceous substratum and with has not been considered in the discussion. the highest altitudes in the study area are included in this C. Low altitude sites with intermediate polluted and group. It is similar to the previous group in relation to mineralized waters, as shown by the average levels of pollution and altitude. The siliceous substratum appears phosphorus, chloride and conductivity (Table 3). The as the main difference, as revealed by the average con high concentrations of silicate (4.11 mg/1) reveal the sili ductivity and concentration of silicate (Table 3). ceous nature of the substratum. Tr-1, however, does not The frequencies of occurrence of all species in the fully fit into this scheme. Its faunistic data are not consis TWINSPAN site groups are given in Table 4. Species tent with the rest of the group either, so we consider it a with the highest incidence in group A are Oulimnius trog misclassified site. lodytes, Esolus pygmaens, and, to a lesser extent, Oulim D. Sites from medium-altitude reaches. As a whole, nius rivularis. They were the species most strongly they show no evident relation to mineralization or pollu associated with contaminated reaches. Elmis maugetii tion, as shown by their position in the centre of the CCA maugetii, Esolus parallelepipedus, and Limnius opacus are also well represented in this group, although their dis-

40 Or3 OrB Or9 Tu5 E5 Du3 J Tr2 Tu3 Trl L3 L5 Or5 Or6 Orl Or2 Or4 Tu4 L4 Om3 Om4 E4 Du2 El E2 E3 Dul Tul L2 Om2 Toi To2 Oml Va <------A ------<■ B ------C ------» ------D ------E ------► •<—— F----- ► «-G -*-

Fig. 4. TW1NSPAN classification o f sampling sites.

Table 4. Frequency o f occurrence (%) o f species in TWINSPAN site groups.

A B c D E F G Dupophilus brevis Mulsant & Rey, 1872 45 57 Elmis aenea (Müller, 1806) 9 29 75 100 Elmis maugetii maugetii Latrellle, 1798 50 20 100 71 50 50 Elmis rioloides (Kuwert, 1890) 27 86 Esolus angustatus (Müller, 1821) 14 50 100 Esolus parallelepipedus (Müller, 1806) 50 40 45 71 Esolus pygmaeus (Müller, 1806) 75 Limnius opacus Müller, 1806 50 82 29 Limnius perrisi carinatus (Pérez-Arcas, 1865) 29 50 50 Limnius volckmari (Panzer, 1793) 29 Oulimnius rivularis (Rosenhauer, 1856) 75 100 100 Oulimnius troglodytes (Gyllenhäl, 1827) 100 55 Oulimnius tuberculatus (Sharp, 1872) 43 Riolus subviolaceus (Müller, 1817) 25 Stenelmis canaliculata (Gyllenhäl, 1808) 100 43 Hydraena testacea Curtis, 1830 80 Hydraena affusa D ’Orchymont, 1936 50 Hydraena barrosi D ’Orchymont, 1936 100 Hydraena brachymera D’Orchymont, 1936 25 60 9 100 100 Hydraena cordata Schaufuss, 1883 14 25 Hydraena corinna D ’Orchymont, 1936 43 Hydraena inapicipalpis Pic 1918 86 50 Hydraena sharpi Rey, 1886 14 Hydraena stussineri Kuwert, 1888 29 Hydraena minutissima Stephens, 1829 50 Hydraena emarginata Rey, 1885 27 14 100 100 Hydraena exaspérala D ’Orchymont, 1935 25 100 40 73 100 50 50 Hydraena hispánica Ganglbauer, 1901 14 Hydraena ibérica D’Orchymont, 1936 9 57 25 50 Limnebius gerhardti Fleyden, 1870 20 9 Limnebius truncatellus (Thunberg, 1794) 20 9 14 50 50 Ochthebius heydeni Kuwert, 1887 50 tribution is much wider. These species (especially the for could be considered as widely distributed species tolerat mer three) constitute an assemblage occurring in low alti ing moderately polluted waters. tude, eutrophicated reaches. Their position in the CCA Most species in groups C and D were well represented graph supports this view. However, all except Esolus pyg- in other sites. They were present over a relatively wide maeus were also found in other groups. Therefore, they range of environmental conditions. Elmis maugetii, Eso lus parallelepipedus, Hydraena brachymera, Hydraena

41 exaspérala, and Linmebius truncatellus were the most This study emphasized that other variables, such as wa widely distributed species in this basin. They could be ter mineralization and pollution by inorganic nutrients, considered as eurytopic species, since they are present in were also important. Both showed a strong correlation a great number of site groups and show no clear prefer with the second ordination axis and produced a good dif ence for any of them. ferentiation of site groups. Group E is characterized by Dupophilus brevis, Elmis There was an apparent lack of an assemblage typical of rioloides, Hydraena inapicipalpis, and Hydraena ibérica. polluted reaches. Only Esolus pygmaeus seems restricted Other species are exclusive from this group, but their fre to these areas, while other species ( Oulimnius troglodytes, quency is lower: Limnius volckmari, Oulimnius tubercu- Oulimnius rivularis), although present in these points, oc latus, Hydraena corinna, Hydraena sharpi, Hydraenacurred in other sites as well. Therefore, the existence of stussineri, and Hydraena hispánica. They form an assem relatively tolerant taxa is evident, but no group of species blage occurring in clean, low-mineralized, medium- exclusive to polluted areas has been found. Variables re altitude waters. They are all situated on the lowest end of lated to low altitude, in contrast, appeared to be dominant the CCA plot. and hide partially the effect of contamination. The fact Species most related to groups F and G are Elmis that the pollution level in the basin was not high must also aenea, Esolus angustatus, Limnius perrisi carinatus,be taken Hy into account; the results might be quite different draena affusa, Hydraena barrosi, Hydraena minutissima, in other circumstances. In general, both Elmidae and Hy- Hydraena emarginata, and Ochthebius heydeni. They draenidae from lotic environments are considered non- constitute an assemblage from high altitude, little tolerant, although they sometimes may occur (especially eutrophicated sites. Their position on the CCA diagram the former) in polluted areas. In this respect, Musso et al. confirms this preference. Hydraena ibérica is also impor (1991) found no elmids in heavily polluted rivers, while tant in this group, as it was in group E. Riolus sub- Foster et al. (1992) considered them sensitive species, but violaceus, Hydraena affusa, and Hydraena minutissima collected some in very polluted sites. Lotic species of Hy (group F) occurred only on calcareous substratum. The draena, on the other hand, seem to be sensitive to organic remaining species were limited to siliceous areas or were pollution as Cuppen (1993) states. In the Orbigo Basin, a indifferent. similar pattern is noted, with no Hydraenidae and few species of Elmidae in the most contaminated reaches. DISCUSSION Anyway, it remains to be seen what the responses would The application of multivariate techniques in relation to be to stronger eutrophication. the ecological responses of individual species has shown An extensive set of species was limited to unpolluted similar results to those obtained in previous papers waters (those occurring in site groups E, F and G). How (García Criado & Fernández Aláez, 1994, 1995) by ever, the absence of sites as clean as headwaters in the means of ecological profiles. The latter offers a more de lowest reaches of the basin (as shown by the CCA plot tailed view on the autecology of each species and its re and personal experience) does not allow to definitively sponse to a particular parameter. Multivariate techniques infer what is responsible for this distribution: pollution or constitute an additional and very useful approach since geography. they provide information on the interaction of a set of en The response of beetles to water mineralization seems vironmental variables and their relationship to assemblage to define, at least, a community typical of siliceous, distribution. scarcely-mineralized areas. It includes species present in Several parameters are related to water beetle distribu sites from groups E and G. The existence of an assem tion in this basin. Altitude is the most important one, blage located in sites with a calcareous substratum is not while pollution and mineralization can be taken as com so clear. Three species in group F ( Hydraena affusa, Hy plementary but also important variables. These variables draena minutissima and Riolus subviolaceus) were only by themselves do not determine the distribution of the found in these sites, but too few specimens (3 of each beetle species, but they do reveal impacts or environ species) were collected to obtain representative data. mental features. Phosphorus and chloride concentration, The pattern found in the Orbigo River Basin, where for example, are indications of agricultural and urban- longitudinal zonation is the main factor and pollution the derived pollution. Altitude itself does not cause a differ secondary one, is usual in rivers with moderate contami ence in faunistical composition. Flowever, it is a good nation. Bournaud et al. (1980) have observed a similar reflection of a number of variables, such as water tem situation in the Furans River (France) when analysing perature, gradient and current velocity, capable of pro macroinvertebrates by means of Factorial Correspon ducing changes in the assemblages. dence Analysis. It has been possible to distinguish a typical low-reach Our results derive from a restricted area with limited community (species dominating group A) and another as environmental variation. Studies involving more taxa and semblage characteristic of headwaters (species in groups a greater range of habitats have shown that substratum F and G). Boumaud et al. (1980) have already pointed out type (specially the presence of silt) is an essential parame that Elmidae are good indicators of longitudinal zonation ter in water beetle distribution (Boumaud et al., 1992; of streams. Eyre et al., 1993). Cuppen (1993) has found stream veloc ity to be the most significant factor influencing Hydraena

42 distribution. In our case, no differentiation of that kind G arcía C riado F. & F ernández Aláez M. 1995: Aquatic Cole can be made since sampling has only been carried out in óptera (Hydraenidae and Elmidae) as indicators o f the chemi lotie environments with a cobble substratum. However, cal characteristics o f water in the Orbigo River basin (N-W this may be an advantage because in this way other pa Spain). Ann. Limnol. 31: 185-199. G arcía C riado F., R égil C ueto J.A. & Fernández Aláez M. rameters, such as pollution, which could otherwise be 1994: Aspectos ecológicos de la familia Hydraenidae (Cole concealed, are better appreciated. The pH range is limited óptera) en la cuenca del río Orbigo (N.O. España).Zool. Bae- to circumneutral or moderately basic values in this basin; tica 5: 11-25. otherwise it would no doubt be a decisive factor (Eyre et G arcía C riado F., F ernández Aláez M . & R égil C ueto J.A. ah, 1993). 1995: Datos sobre la ecología de la familia Elmidae en la The use of CCA has allowed us to determine approxi cuenca del río Orbigo (León, España). Boll. Soc. Entomol. mate preferences in relation to a set of variables by means Ital. 126: 200-210. of the interpretation of species position in the graph. In G arrido J. 1990:Adephagay Polyphaga acuáticos (Coleóptera) combination with TWINSPAN, it has made it possible to en la provincia fltogeográfica Orocantábrica (Cordillera establish characteristic assemblages from a number of en Cantábrica, España). PhD thesis, León University, 427 pp. Jeffries M. 1994: Invertebrate communities and turnover in wet vironments and define their special features. This ap land ponds affected by drought. Freshwater Biol. 32: proach is more interesting than the classical consideration 603-612. of single indicator species, as many authors emphasize H ill M.O. 1979: TWINSPAN, A FORTRAN program for ar nowadays (Boumaud et ah, 1992; Malmqvist & Maki, ranging multivariate data in an ordered two-way table by 1994; Ribera & Foster, 1992). Moreover, this study rein classification o f the individuals and attributes. Ecology and forced the view that water beetles (Hydraenidae and El- Systematics, Cornell University, New York, 31 pp. midae), are good descriptors of environmental M almqvist B. & M àki M. 1994: Benthic macroinvertebrate as characteristics (Boumaud et ah, 1980; Eyre et ah, 1986). semblages in north Swedish streams: environmental relation Habitats, even in a rather homogeneous area, can be dif ships. Ecography 17: 9-16. ferentiated by species of these beetles. M illet X. & P rat N. 1984: Las comunidades de macroinverte- brados a lo largo del río Llobregat.Limnetica 1: 222-233. REFERENCES M onzón A., V ítor Cortes R.M., de Koe T. & M eló de C ar valho L.H. 1990: Técnica de análisis directa de gradiente en Armitage P., Pardo I. & B rown A. 1995: Temporal constancy la ordenación de las comunidades de macrobentos en la o f faunal assemblages in “mesohabitats” - Application to cuenca del río Tua. Sci. Gerund. 16(1): 133-146. management? Arch. Hydrobiol. 133: 367-387. Musso J.J., P révôt G., L égier P. & P layoust C. 1991: Contri Bournaud M., Keck G. & R ichoux P. 1980: Les prélèvements bution à la connaissance des cours d’eaux méditerranéens de des macroinvertébrés benthiques en tant que révélateurs de la basse altitude: le réseau hydrographique de l’Arc (Bouches- physionomie d’une rivière. Ann. Limnol. 16: 55-75. du-Rhône, France). Etat des peuplements en référence aux Bournaud M., R ichoux P. & U sseglio -P olatera P. 1992: An perturbations anthropiques. Ann. Limnol. 27: 75-85. approach to the synthesis o f qualitative ecological informa P etts G.E. & B ickerton M.A. 1994: Influence o f water abstrac tion from aquatic Coleóptera communities. Regul. Rivers Res. tion on the macroinvertebrate community gradient within a Manag. 7: 165-180. glacial stream system: La Borgne d’Arolla, Valais, Switzer Collinson N.H., B iggs J., C orfield A., H odson M.J., W alker land. Freshwater Biol. 32: 375-386. W hitfield W illiams D., M. & P.J. 1995: Temporary and per P uig M.A. 1983: Distribución y ecología de las especies de El manent ponds: An assessment o f the effects o f drying out on midae (Col.; Dryopoidea) de la cuenca del río Llobregat. Bol. the conservation value o f aquatic macroinvertebrate commu Asoc. Esp. Entomol. 7: 211-219. nities. Biol. Consent. 74: 125-133. R idera I. & Foster G.N. 1992: Uso de coleópteros acuáticos C uppen J.G.M. 1993: Distribution and ecology o f Hydraena como indicadores biológicos (Coleóptera).Elytron 6: 61-75. Kugelann in the Netherlands (Coleóptera: Hydraenidae). Rico E. 1996: Distribución de los Elmidae (Coleóptera: Dryo Tijds. Entomol. 136: 1-10. poidea) en la Península Ibérica e Islas Baleares. Graellsia 52: D íaz Pazos J.A. 1991:Estudio taxonómico y ecológico de los115-147. Hydraenidae (Coleóptera) de la cuenca del río Landro (Lugo, R utt G.P., W eatherley N.S. & O rmerod S.J. 1989: Microhabi- España). PhD thesis. Santiago de Compostela University, 515 tat availability in Welsh moorland and forest streams as a de PP- terminant o f macroinvertebrate distribution. Freshwater Biol. Eyre M.D., B all S.G. & F oster G.N. 1986: An initial classifi 22: 247-261. cation o f the habitats o f aquatic Coleóptera in North-East Sáinz Cantero C.E., Sánchez O rtega A. & Alba T ercedor J. England. J. Appl. Ecol. 23: 841-852. 1987: Distribución y autoecología de Hydraenidae (Col.) en Eyre M.D., Pilkington J.G., Carr R., M cB lane R.P., R ushton Sierra Nevada (España). Bol. Asoc. Esp. Entomol. 11: S.P. & Foster G.N. 1993: The running-water beetles (Coleóp 355-365. tera) o f a river catchment in northern England. Hydrobiologia Soler A.G., M ontes C. & Ramírez L. 1976: Analyse factorielle 264: 33-45. des biocénoses de Coléoptères aquatiques des marais (ma Foster G.N., N elson B.H., B ilton D.T., Lott D.A., M erritt R., risma) du bas Guadalquivir (Espagne). Ann. Limnol. 12: W eyl R.S. & Eyre M.D. 1992: A classification and evalua 89-103. tion o f Irish water beetle assemblages. Aquatic Consent. Ma T er B raak C.J.F. 1986: Canonical Correspondence Analysis: a rine Freshwater Ecosyst. 2: 185-208. new eigenvector technique for multivariate direct gradient G arcía C riado F. & F ernández Aláez M. 1994: Distribución analysis. 67: 1167-1179. longitudinal de Hydraenidae y Elmidae (Coleóptera) en la Ecology cuenca del río Orbigo (León, España).Or sis 9: 37-57.

43 T er B raak C.J.F. 1987: The analysis o f vegetation-environment continentales de la Península Ibérica e Islas Baleares 10. Aso relationships by canonical correspondence analysis. Vegetatio ciación Española de Limnología, 93 pp. 69: 69-77. V erdonsciiot P.F.M. 1995: Typology o f macrofaunal assem V alladares L.F. 1988:Los Palpicornios acuáticos de la problages: a tool for the management o f running waters in The vincia de León. PhD thesis. León University, 454 pp. Netherlands. Hydrobiologia 297: 99-122. V alladares L.F. 1989: Los Palpicornia acuáticos de la provin W right J.F., Moss D., Armitage P.D. & Furse M.T. 1984: A cia de León. II. Hydraena Kugelann, 1794 y Limnebius preliminary classification o f running-water sites in Great Brit Leach, 1815. (Coleóptera: Hydraenidae). Bol. Asoc. Esp. En- ain based on macro-invertebrate species and the prediction of tomol. 13: 313-330. community type using environmental data. Freshwater Biol. V alladares L.F. & M oni es C. 1991: Lista faunística y biblio 14: 221-256. gráfica de los Hydraenidae (Coleóptera) de la Península Ibé Received February 12, 1998; accepted September 4, 1998 rica e Islas Baleares. Listas de la flora y fauna de las aguas