Chironomid (Diptera: Chironomidae) communities in six European glacier-fed streams

Chironomid (Diptera: Chironomidae) communitiesin six European glacier-fed streams

B. LODS-CROZET,* V. LENCIONI,² J . S . OÂ LAFSSON,³ D. L. SNOOK,§ G. VELLE,±J . E . BRITTAIN,** E. CASTELLA* and B. ROSSARO²²

*Laboratoire d'Ecologie et de Biologie Aquatique, University of Geneva, Geneva, Switzerland

²Department of Invertebrate Zoology and Hydrobiology, Museum of Natural Science of Trento, Trento, Italy

³Institute of Biology, University of Iceland, Reykjavik, Iceland

§School of Geography and Environmental Sciences, University of Birmingham, Birmingham, U.K.

±Museum of Zoology, University of Bergen, Bergen, Norway

**Freshwater Ecology and Inland Fisheries Laboratory, University of Oslo, Oslo, Norway

²²Department of Biology, Section Ecology, University of Milano, Milano, Italy

SUMMARY

1. A study on glacial stream ecosystems was carried out in six regions across Europe, from

Svalbard to the French Pyrenees. The main aim was to test the validity of the conceptual

model of Milner & Petts (1994) with regard to the zonation of chironomids of glacier-fed

rivers along altitudinal and latitudinal gradient.

2. Channel stability varied considerably, both on the latitudinal and altitudinal scale,

being lowest in the northern regions (Svalbard, Iceland and Norway) and the Swiss Alps.

Water temperature at the upstream sites was always <2 °C.

3. There was a prominent difference in taxonomic richness between the Alpine and the

northern European regions, with a higher number of taxa in the south. In all regions, the

chironomid community was characterized by the genus Diamesa and the subfamily

Orthocladiinae. Of a total of 63 taxa recorded, two (Diamesa bertrami and Orthocladiusfrigidus) were common in all the regions except Svalbard.

4. On the basis of cluster analysis, seven distinct groups of sites were evident amongst

glacial-fed systems of the ®ve regions (Pyrenees excluded). This classi®cation separated

the glacier-fed streams on geographical, latitudinal and downstream gradients.

5. Canonical Correspondence Analysis (CCA) of environmental variables was carried out

using 41 taxa at 105 sites. Slope, water depth, distance from source, water temperature and

the Pfankuch channel stability index were found to be the major explanatory environ-

mental variables. The analysis separated Diamesinae and typical upstream orthoclads

from the other chironomids by low temperature and high channel instability.

6. In all six regions, Diamesa was present closest to the glacier. Within 200 m of the glacier

snout, other genera of Diamesinae were found together with Orthocladiinae. Pioneer taxa

like Diamesa species coexisted with later colonizers like Eukiefferiella minor/®ttkaui in

relatively unstable channels.

7. The longitudinal succession of chironomid assemblages across altitudinal and latitu-

dinal gradients in glacial streams followed the same pattern, with similar genera and

groups of species. The general aspects of the conceptual model of Milner & Petts (1994)

were supported. However, Diamesa species have wider temperature limits than predicted

and other Diamesinae as well as Orthocladiinae colonize metakryal habitats.

Correspondence: Brigitte Lods-Crozet, Laboratoire d'Ecologie et de Biologie Aquatique, University of Geneva, 18, ch. des

Clochettes, CH-1206 Geneva, Switzerland. E-mail: [email protected]

Freshwater Biology (2001) 46, 1791±1809

Ó 2001 Blackwell Science Ltd 1791

Keywords: alpine, arctic, glacial stream, Chironomidae, latitudinal distribution

Introduction

The cold temperatures and marked seasonality of

Alpine and arctic rivers limit the potential types of

insect life cycles (Rossaro, 1991a, b; Danks, 1999).

Detailed information about life cycles in these regions

is still fragmentary. Glacial meltwater streams, de®ned

as kryal biotopes by Steffan (1971), are characterized

by very cold (near 0 °C), highly turbid and fast

¯owing waters with low channel stability and sea-

sonal ¯ow regimes with high diel peaks in summer.

Most previous research on glacier-fed streams has not

primarily focused on chironomid communities

(Thienemann, 1936; Dorier, 1937; Saether, 1968;

Steffan, 1971; Serra-Tosio, 1973; Kownacki, 1991) and

only a few studies have compared streams in different

regions (Kownacka & Kownacki, 1975; Kawecka,

Kownacki & Kownacka, 1978; Milner & Petts, 1994;

Lindegaard & Brodersen, 1995). The subfamily Diam-

esinae `and especially the genus Diamesa' are typically

the ®rst taxa to colonize streams immediately down-

stream of source glaciers. Diamesinae are by virtue of

their narrow ecological niche (mainly cold-stenother-

mal species) and widespread distribution through the

Palaearctic region, is a very pertinent group for

zoogeographic and ecological research (Serra-Tosio,

1973; Rossaro, 1995).

The gradient of environmental conditions that

occurs as a function of altitude or latitude within

European streams offers excellent opportunities to

investigate factors which in¯uence the diversity,

composition and abundance of stream organisms

(Ward, 1986). Stream habitats that are frequently

and/or intensely disturbed are expected to exhibit

low species richness, because few species are able to

colonize them during the brief periods between

disturbance events or to tolerate high disturbance

intensity (Townsend, Scarsbrook & DoleÂdec, 1997).

Likewise, Townsend (1989) suggested that even

where competition or predation have been shown to

play a role of shaping stream communities, the tem-

poral phenomena of disturbance and colonization are

invariably of fundamental importance. Stream benthic

communities occurring under frequent disturbances

comprise species that have been variously referred

to as fugitive or r-selected species (Pianka, 1978).

The rapid colonization ability of chironomids enables

them to dominate early in colonization processes

(Ladle et al., 1985; Townsend, 1989; Ruse, 1994).

In an attempt to explain the primary physical,

chemical and biological factors that determine macro-

invertebrate distributions downstream of glaciers

across Europe, Milner & Petts (1994) proposed a con-

ceptual model to explain variations in the zoobenthic

community structure within and between glacier-fed

streams. This model assumed that the primary

physical variables in¯uencing the macroinvertebrates

succession in glacial streams are maximum water

temperature and channel stability, which both increase

downstream from the glacial margins. As chironomids

are a major element in the model, we have focused our

study on two objectives: (i) to test the sensitivity of

Milner & Petts' conceptual model concerning the

zonation of stream chironomids in glacier-fed rivers

and (ii) to examine whether longitudinal succession of

the chironomid assemblages in glacial streams follows

the same pattern across altitudinal and latitudinal

gradient. This is the ®rst investigation of chironomid

assemblages based upon uni®ed sampling and ana-

lytical procedures at a range of sites along a wide

latitudinal gradient.

Methods

Study sites

The study was carried out in six glacier-melt dominated

streams, the Taillon (TAI, French Pyrenees), the Conca

(CON, Italian Alps), the Mutt (MUT, Swiss Alps),

Daleleva (BRI, Western Norway), W-JoÈkulsaÂ (WJO,

Iceland) and Bayelva (BAY, Svalbard). These streams

form a latitudinal and altitudinal gradient across

Europe from the Pyrenees in the south to Svalbard in

the north. A detailed description of their location and

characteristics is given in other papers in this volume

(Brittain et al., 2001a; Gislason et al., 2001; Lods-Crozet

et al., 2001; Maiolini & Lencioni, 2001; Snook & Milner,

2001) but their principal characteristics are summar-

ized in Table 1. In general the glacial systems studied

were smaller in the southern part of Europe (Pyrennes

and the Alps) than in the northern countries, both

with respect to glacial area and discharge.

In each stream, four permanent study transects

were established within 15-m long sites representing

1792 B. Lods-Crozet et al.

Ó 2001 Blackwell Science Ltd, Freshwater Biology, 46, 1791±1809

characteristic reaches that were identi®ed on the basis

of valley and channel geomorphology and the com-

position of aquatic communities. The ®rst site was as

close to the glacial snout as possible, and the second

one within 1000 m of the snout and upstream of any

major tributaries. The furthermost downstream site

was chosen where, within zoogeographical con-

straints, a fully developed invertebrate community

occurred [as de®ned in the conceptual model of

Milner & Petts (1994)], i.e. where stone¯ies, caddis¯ies

and may¯ies families were represented together with

chironomids (Orthocladiinae and Chironominae) and

other dipteran families. Four to eight sites were

located in each study catchment to represent the

different channel sectors.

In each river system, except Bayelva on Svalbard,

®eld surveys were carried out during three periods in

both 1996 and 1997: immediately postspring snow-

melt (June), in mid-summer during the ice melt

(August) and at low water level (September). The

snowpack prevented some investigations at upstream

sites in June. As the ice free season on Svalbard is

short, Bayelva was sampled only during early July

and late August 1997.

Geomorphological and environmental variables

Geomorphological descriptions (width of valley

¯oor, width of all active channels, slope) were

carried out at each site. The stream bottom com-

ponent of Pfankuch's index (Pfankuch, 1975) was

used to assess channel stability by scoring ®ve

variables (rock angularity, bed-surface brightness,

particle packing, percentage stable materials, scour-

ing and aquatic vegetation), with high total scores

representing unstable channels at the site scale.

This index gave through a rapid and simple

assessment, a real measure of stream disturbance

because it is strongly correlated both with ¯ood

frequency and degree of bed movement (Townsend

et al., 1997).

During a 5 day sampling period during each ®eld

survey, water temperature, water level, discharge,

conductivity and suspended solids were monitored at

minimum and maximum ¯ows at the upstream and

downstream sites. Discharge was determined with a

¯ow meter (depth±velocity transects), at a gauging

station or by the salt dilution method (Hongve, 1987).

Water temperature was monitored continously atTab

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Chironomid communities in glacial streams 1793


most river systems by digital loggers (details in other

papers in this volume).

At each of the four transects within each site, the

wetted channel width to a maximum depth of 0.5 m

and the depth/velocity pro®le were assessed. The

bed-sediment composition was assessed visually or

by contact at each point of the depth/velocity

pro®les.

Biological sampling

Within each sampling site, ten standardized kick

samples (30 s) were collected for invertebrates using a

standard pond net (30 cm ´ 30 cm) with a mesh size of

250 lm. In the case of the Icelandic system, ten stones

were sampled at each site and macroinvertebrates

rinsed off, the surface area of each stone was traced on a

paper and its area used when calculating the inverteb-

rate density (Gislason, OÂ lafsson & Adalsteinsson,

1998). At the kick sample scale, the dominant sediment

particle size, water depth and six consecutive measures

of ¯ow velocity were taken. In addition, three stones

were collected at random in each site and benthic algae

were scraped off on the upper surface (area

3 cm ´ 3 cm) and washed onto a Whatman GF/C ®lter

paper. Chorophyll a was determined spectrophoto-

metrically in the laboratory (APHA, 1992).

The chironomid material used for this study ori-

ginates only from larvae and pupae collected by kick

or stone samples in the streams. The animals from ®ve

to ten kick samples and all stone samples were sorted,

counted and identi®ed. Random subsampling was

adopted when chironomid abundance exceeded 30

and 100 for Norwegian and Icelandic rivers, respect-

ively.

Within each subfamily, a taxonomic limit was

imposed by the larvae and further identi®cation with

pupae was ignored, unless all pupae belonged to one

species. In that case, the larvae were also ascribed to

this species. On account of taxonomic problems with

Diamesa larvae, it was decided to establish eight dis-

crete groups which were: (1) Diamesa aberrata gr.; (2)

D. bertrami Edwards; (3) D. damp® gr.; (4) D. davisi gr.;

(5) D. latitarsis gr.; (6) D. steinboecki Goetgh.; (7)

D. zernyi gr./cinerella gr.; (8) Diamesa gr. A:. which

included the ®rst and second instars of D. bertrami,

D. davisi gr., D. latitarsis gr. and D. steinboecki. Iden-

ti®cation keys and species descriptions were selected

from the European literature (Thienemann, 1952;

Serra-Tosio, 1967; Saether, 1968; Rossaro, 1980, 1981,

1982; Ferrarese & Rossaro, 1981; Cranston, 1982;

Ferrarese, 1983; Wiederholm, 1983; Wiederholm,

1986; Makarchenko, 1985; Nocentini, 1985; Langton,

1991; Schmid, 1993; Janecek, 1998). The chironomids

from the Pyrenees system were not identi®ed to the

same extent as at the other sites and were therefore not

included in multivariate analyses. Abbreviations of

species names were used according to a standardized

coding system developed by Schnell et al. (1999).

Data analysis

The elementary units used in all the analyses were

site data on a given date, i.e. the average of 5±10

replicate kick or stone samples. The quantitative

faunal data, expressed as the number of individuals

m±2, were processed by correspondence analysis

(CA), which provides a reciprocal ordination of the

species and the sampling units (106 selected sites). All

the data on chironmid densities were [log10(x + 1)]

transformed prior to analysis. A cluster analysis by

Ward's method (Ward, 1963), which grouped samp-

ling sites according to the similarity of their chiron-

omid assemblages, was carried out using the factorial

scores of the sites in the previous CA as a summary of

the faunal data. Following Roux (1991), the contribu-

tion (CV(j,p)) of each taxon (j) to each site cluster (p)

was calculated as:

�CV�j;p�� Zpj ÿ Zj�2=Rj�Zpj ÿ Zj�2

with Zpj � average of taxon j in cluster p, Zj � overall

average of taxon j.

Canonical correspondence analysis (CCA) (ter

Braak, 1986) was used to determine relationships

between the environmental properties of each site

and their respective chironomid composition. In the

CCA biplots, axes represent the most important

environmental gradients along which the chirono-

mid fauna was distributed. The signi®cance of the

CCA axes was determined by Monte Carlo permu-

tation testing (1000 permutations) of the eigenvalues

(Fraile, Escou®er & Raibaut, 1993). The variations in

abundance of the most characteristic chironomid

taxa in relation to temperature were described using

second order polynomial regression curves. All cal-

culations were carried out using the ADE-4 software

(Thioulouse et al., 1997).



Results

Habitat characteristics

A summary of the physico-chemical and biological

data in the six glacial streams is given in Table 2.

The site slope of the six systems decreased with the

altitude range of the glacial rivers and with the

latitudinal gradient. Pfankuch's Index of channel

stability varied from 58 (highly unstable stream

bottom) to 18 (stable stream bed). Conductivity was

very low for the Italian and Norwegian systems

(£13 and £10 lS cm±1, respectively), whereas the four

other rivers had conductivities up to 80 and even

140 lS cm±1 (Swiss Alps). Algal biomass, measured as

chlorophyll a concentration, reached maximum values

of 10.0 mg m±2 in most of the glacial systems except

in Dalelva and Bayelva where the concentrations

reached 30.6 (BRI02) and 19.3 (BAY04) mg m±2,

respectively. The Alpine systems (Pyrenees and the

Alps) were dominated by boulders and cobbles while

the Dalelva, W-JoÈkulsaÂ and Bayelva sites were char-

acterized by gravel, sand and silt.

Mean current velocities were comparable in the

Alpine and Pyrenean sites (Taillon, Conca and Mutt:

Table 2 Summary of physical, chemical and periphyton variables at the site scale (�SD: interdate variation) for the study streams

Site

no.

Distance

from the

snout (m)

Site

slope

(m m)1)

Water

width

(m)

Water

depth

(m)

Pfankuch

Index

Speci®c

conductivity

(lS cm)1 at 20 °C)

Chlorophyll a

(mg m)2)

TAI01 50 0.079 1.8 (0.03) 0.14 (0.01) 41 72.2 (24.7) 0.91

TAI02 900 0.085 2.0 (0.25) 0.09 (0.02) 30 80.6 (21.9) 1.91 (0.85)

TAI03 1425 0.041 3.3 (0.06) 0.14 (0.03) 32 77.3 (20.0) 3.59 (1.05)

TAI35 1500 0.03 4.7 (2.0) 0.16 (0.07) 21 84.0 (41.5) 1.23 (1.23)

CON00 310 0.40 0.7 0.07 18 7.0 (4.4) 2.12 (1.10)

CON01 710 0.13 1.5 0.06 18 7.9 (5.8) 6.77 (3.55)

CON02 1070 0.28 1.8 0.07 32 7.4 (2.6) 6.66 (5.85)

CON03 1520 0.22 2.3 0.07 25 8.5 (2.6) 1.06 (0.56)

CON04 2600 0.02 6.3 0.14 34 10.1 (0.9) 2.60 (1.59)

CON05 2740 0.07 4.8 0.14 27 10.0 (0.9) 2.93 (0.75)

CON08 4600 0.13 15.7 0.13 19 10.2 (2.1) 2.34 (1.28)

MUT01 5 0.1 3.5 (3.4) 0.05 (0.02) 58 27.4 (0.4) 0.16 (0.14)

MUT02 200 0.24 5.1 (3.37) 0.04 (0.01) 38 66.8 (37.8) 0.57 (0.68)

MUT03 350 0.3 7.9 (1.94) 0.06 (0.01) 37 70.6 (24.1) 1.87 (1.07)

MUT04 1700 0.17 5.2 (0.55) 0.16 (0.04) 33 139.0 (49.6) 1.86 (0.22)

MUT05 3600 0.18 4.6 (1.6) 0.21 (0.06) 29 118.6 (36.5) 3.54 (0.15)

BRI01 100 0.034 18 0.25 (0.22) 36 8.2 (3.3) 28.16 (31.74)

BRI02 700 0.015 7 0.30 (0.20) 55 6.6 (4.8) 30.64 (7.67)

BRI03 2000 0.070 8.5 0.31 (0.13) 39 7.0 (4.9) 20.75 (6.41)

BRI04 3300 0.021 15.1 0.31 (0.13) 51 9.3 (4.6) 12.01 (6.39)

BRI05 7100 0.006 9.3 0.49 (0.14) 41 9.1 (4.2) 22.62 (21.10)

WJO01 5 0.005 3.5 (1.0) 0.07 (0.029) 55 10.1 (0.3) 0.09

WJO15 500 0.013 5.1 (0.14) 0.18 (0.03) 34 8.1 (0.2) 0.46 (0.44)

WJO1c 3500 0.004 8.5 (0.71) 0.20 (0.07) 51 28.6 (26.4) 0.44 (0.47)

WJO02 1400 0.006 6.0 (1.4) 0.19 (0.07) 38 16.3 (8.8) 0.78 (0.55)

WJO2b 3000 0.005 12.7 (3.16) 0.44 (0.06) 47 49.6 (6.1) 0.78 (1.32)

WJO2c 22 000 0.007 8.2 (3.9) 0.25 (0.07) 44 77.5 (13.1) 0.05 (0.02)

WJO03 4500 0.012 8.4 (2.1) 0.39 (0.09) 28 27.5 (15.5) 0.34 (0.08)

WJO35 7500 0.008 16.8 (0.28) 0.23 (0.04) 41 17.3 (5.7) 0.36 (0.38)

WJO04 22 500 0.006 36.0 (2.5) 0.44 (0.07) 39 56.3 (17.4) 0.08 (0.03)

WJO05 42 000 0.014 27.5 (1.0) 0.55 (0.07) 21 81.4 (12.8) 1.24 (0.93)

WJO06 45 000 0.009 34.0 (1.0) 0.60 (0.10) 35 72.1 (20.2) 0.31 (0.21)

BAY01 300 0.024 10.2 (5.0) 0.21 (0.02) 38 37.6 (10.4) 0.12 (0.002)

BAY02 1200 0.006 31.3 (1.66) 0.18 (0.01) 54 49.2 (12.4) 0.96 (0.96)

BAY03 1800 0.006 38.1 (21.0) 0.17 (0.04) 58 63.5 (23.3) 5.3 (4.7)

BAY04 2900 0.008 22.2 (7.42) 0.17 (0.01) 44 81.7 (28.6) 19.3 (8.7)

TAI: Taillon (Pyrennees); CON: Conca (Southern Alps); MUT (Northern Alps); BRI: Dalelva (W-Norway); WJO: W-JoÈkulsaÂ (Iceland);

BAY: Bayelva (Svalbard).



0.60 � 0.22 m s±1); higher current velocities were

recorded in Bayelva (0.82 � 0.14 m s±1). Low values

of suspended sediment were recorded in the Italian

stream (mean of 8.1 mg L±1), followed by the Nor-

wegian (30.6 mg L±1), Pyreneean (45.2 mg L±1) and

Svalbard (86.7 mg L±1) streams, but much higher

values were found in the Swiss and Icelandic streams

(797.5 and 457.1 mg L±1, respectively).

At the upstream sites, the mean and maximum

water temperature was almost always below 2 °C.

The water temperature recorded during the faunal

surveys was signi®cantly correlated with the maxi-

mum temperature (R2 � 0.61, P < 0.001); it was the

only temperature variable retained in the mutivariate

analysis as it was available for all sites and dates.

Latitudinal distribution of chironomid assemblages

A decrease in chironomid taxa richness with latitude

from the Alps to the Svalbard was observed (Table 3).

The most taxa rich subfamilies in the six glacier-fed

rivers were Diamesinae and Orthocladiinae (12 and 42

taxa, respectively). In terms of richness, the Diame-

sinae : Orthocladiinae ratio was relatively constant

(30±40%) across the European latitudinal gradient.

At the generic and species level, the highest taxa

richness was recorded in the Italian Alps (42 taxa) and

the lowest in Bayelva (seven taxa). From a total of 63

taxa (Appendix 1), two species, D. bertrami and

Orthocladius (O.) frigidus (Zetter.), had the widest

latitudinal distribution, only being absent in Bayelva

(Svalbard). In terms of mean chironomid abundance,

no distinct patterns were apparent along the latitudi-

nal gradient (Table 3). The highest mean chironomid

densities were recorded in the Northern Alps (Mutt),

followed by the Central Icelandic river, the Western

Norwegian one, the Pyrenees (Taillon), the Italian

Alps and Svalbard. Diamesinae accounted for 83±97%

of the total abundance except in the Italian and

Icelandic systems where they remained below 50%.

The contribution of Chironominae and Tanypodinae

was low, both in terms of density and species

richness.

Ordination and classi®cation of river systems basedon their chironomid assemblages

Five river systems were considered in the following

analyses (Conca, Mutt, Dalelva, W-JoÈkulsaÂ and

Bayelva). Ordination of the 63 taxa by 106 sites/dates

data matrix using CA demonstrated a strong stream-

speci®c effect along the ®rst two factorial axes (Fig. 1).

The species-poor Svalbard system occupied the central

position of the ordination. The ®rst axis divided the

Italian system from the three others while the second

axis spread the Swiss, Norwegian and Icelandic ones.

Table 4 summarizes the seven groups of sites

resulting from the cluster analysis with typical taxa

found in each group. This classi®cation separated

the glacial systems on both a geographical-latitudi-

nal and a downstream gradient. Diamesa steinboecki,

D. latitarsis gr. and Diamesa gr. A (group 1) character-

ized the uppermost sites (c. the ®rst 350 m) of the

Alpine streams. Two groups (2 and 3) split the Italian

system into its upstream and downstream sites. In

group 2, O. rivicola gr., D. steinboecki, Pseudokiefferiella

parva (Edwards) were the most dominant taxa bet-

ween 750 and 1500 m from the glacier snout. Group 3

comprised the downstream chironomid communities

characterized by taxa such as Micropsectra atrofasciata

(Kieff.) Tvetenia spp. and Eukiefferiella brevicalcar

(Kieff.)/tirolensis Goetgh. Group 4 comprised four

Table 3 Taxonomic richness and mean abundance expressed as individuals m±2 � 95% Con®dence Level (number of kick

samples) of Chironomidae in the six glacial streams

TAI CON MUT BRI WJO BAY Total

Taxonomic richness 27 42 29 20 20 7 63

Diamesinae 6 9 8 5 4 2 12

Orthocladiinae 16 30 20 14 13 5 42

Chironominae 4 2 1 0 2 0 6

Tanypodinae 1 1 0 1 1 0 3

Mean abundance 1306 � 469 (100) 636 � 106 (209) 2569 � 597 (216) 2010 � 526 (66) 2163 � 511 (233) 114 � 67 (23)

Diamesinae 1085 � 379 215 � 79 2457 � 589 1944 � 520 1005 � 237 100 � 69

Orthocladiinae 192 � 68 301 � 60 111 � 44 65 � 34 1100 � 390 14 � 7

Chironominae 29 � 22 114 � 32 0.5 � 0.3 0 58 � 41 0



taxa characteristic of the Mutt system in the Swiss

Alps: Diamesa latitarsis gr., Orthocladius spp., O. (E.)

luteipes Goetgh. and Paraphaenocladius spp. Six taxa

predominated group 5, which included the whole

Dalelva glacial system, and the upstream sites of the

W-JoÈkulsaÂ (c. from 5 m to 7.5 km distance downstream

from the snout) with D. bertrami, D. latitarsis gr. and

D. bohemani Goetgh./zernyi Edwards. Group 6 encom-

passed the downstream Icelandic sites where E. minor

(Edwards), E. claripennis gr., Orthocladius (O.) frigidus

and Diamesinae juveniles dominated the chironomid

assemblages. The Svalbard glacial stream, Bayelva,

formed the seventh group with three distinct taxa:

Thienemannia spp., Cricotopus fuscus gr. and D. aberrata

gr. However, two sites from Bayelva (BAY02 in July

and BAY03 in August 1997) belong to groups 2 and 3

because of their unindenti®ed juvenile Orthocladiinae.

Longitudinal patterns of chironomid assemblages

downstream of glacial margins

The species composition of chironomids along the

downstream gradient showed that, as expected,

several Diamesa species occurred closest to the

glacial source in the six streams (Fig. 2). However,

within 100 m of the snout, other Diamesinae [e.g.

Pseudokiefferiella parva (in the Alps and Pyrenees) and

Pseudodiamesa arctica (Now.) (Norway)1] were present

in low densities. Depending on the time of year, a few

Orthocladiinae like Heterotanytarsus sp. (Pyrenees),

Eukiefferiella minor (Norway and Iceland) and

Tokunagaia rectangularis gr. (Norway) were also pre-

sent.

In the Alps, D. steinboecki and D. latitarsis gr. were

the most abundant taxa in the uppermost site whereas

D. zernyi/cinerella gr. dominated these sites in the

Nordic countries. The dominant species at the Alpine

glacial margins, D. steinboecki, decreased progressively

in abundance along the downstream gradient, while

Fig. 1 Correspondence analysis (CA) of

106 glacial stream sites according to the

occurrence and abundance of 63 chirono-

mid taxa (a) Small squares represent sites

on a given sampling date, (b) histogram of

eigenvalues.

1Pseudodiamesa arctica (Malloch) is reported from arctic Canada

while Pseudodiamesa nivosa (Goetghebuer) is found in the

Palaearctic. However, Schnell & Willassen (1991) suggest they

are the same species and should be named P. arctica as this is the

oldest name.



the other Diamesa species were still found up to 4 km

downstream from the glacier.

In the subfamily Orthocladiinae, the colonists to

become established closest to the glacier were

O. frigidus (Pyrenees, Swiss Alps, Iceland), O. rivicola gr.

(Italian Alps, Svalbard), Heleniella sp. (Italian Alps),

Eukiefferiella minor/®ttkaui and claripennis gr. (Italian

Alps, Norway, Iceland), Parametriocnemus stylatus Kieff.

(Pyrenees), Tvetenia sp. (Italian and Swiss Alps) and

Thienemannia sp. (Svalbard).

Chironomid richness downstream of the glacial

margins showed similar longitudinal patterns (Fig. 3).

A rapid increase in species richness was apparent

within the ®rst 2 km followed by an asymptotic

tendency or even a decrease in chironomid richness

in the lowermost site (less pronounced in Dalelva and

Bayelva).

Chironomid densities in upstream sites were over-

all very low. Within 5 m of the snout, less than 30

individuals m±2 were found in the Alps and in Iceland

(Fig. 2). With the exception of the Italian system (c. ten

individuals m±2 in downstream sites), Diamesa species

(except D. steinboecki) maintained abundant popula-

tions (100±1000 individuals m±2), even up to 42 km

from the snout in the Icelandic system.

Relationships between fauna and environmental data

CCA was carried out using the distribution of the 41

chironomid taxa occurring in at least 5% of the 106

sites/dates and six environmental variables (Fig. 4).

Slope, water depth and distance from the source (logn)

dominated the ®rst axis explaining 38% of the faunal

distribution. Temperature recorded during the faunal

survey, chlorophyll a and Pfankuch's Index of channel

stability were signi®cant explanatory variables for the

chironomid assemblages on the second axis (34%),

although the inverse trend of chlorophyll a towards

temperature can be explained by the high values

measured in the Dalelva and Bayelva upstream sites

(Table 2). The ®rst axis separated Diamesinae and

typical upstream orthoclads from the other chirono-

mids (mainly other orthoclads) and was correlated

with low temperature and high instability of the chan-

nel bed. The six environmental variables explained

27.5% of the inertia within the faunal data set. Diamesa

bertrami, D. davisi gr., D. latitarsis gr., Pseudodiamesa

arctica, Pseudokiefferiella parva, juvenile Diamesinae,

E. claripennis gr., E. minor/®ttkaui, Heleniella spp. wereTab

le4

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Fig. 2 Longitudinal patterns of chironomid assemblages in glacial streams during two summer periods. Species abbreviations

relate to full names in Appendix 1.



the taxa whose distribution was best explained (more

than 40% of the inertia) by the selected environmental

variables.

The temperature range within which the character-

istic taxa were observed in the ®ve systems (Fig. 5)

showed that the Diamesinae species were able to

maintain populations even at temperatures close to

15 °C. However D. davisi gr. and Pseudodiamesa arctica,

exclusive inhabitants of the Norwegian stream, exhi-

bited a narrower temperature spectrum and their dis-

tribution was well explained by the temperature in

the CANOCOCANOCO model (63 and 46% of the inertia).

Orthoclads were able to colonize and survive in the

metakryal zone in water <2 °C, especially E. minor/

®ttkaui in all the stream systems (Svalbard excep-

ted). Four other species (Eukiefferiella claripennis gr.,

O. frigidus, O. rivicola gr. and Tvetenia bavarica/calvescens)

occurred further downstream in the metakryal zone at

a temperature >2 °C.

Discussion

Longitudinal patterns of chironomids in glacialstreams at different latitudes

The upstream sites of the six glacier-fed streams

studied across Europe supported chironomid assem-

blages dominated by the genus Diamesa. In the Alps,

D. latitarsis gr. and D. steinboecki were the initial

dominant taxa, as mentioned previously by Dorier

(1937), Serra-Tosio (1973), Ferrarese & Rossaro (1981)

and Kownacki (1987, 1991), when mean temperature

was below 2 °C. Diamesa latitarsis gr. was also the

dominant taxon in the Taillon system (Pyrenees),

whereas Diamesa steinboecki was not collected in this

stream during this study. D. steinboecki is a typical

Alpine species of very cold headwaters (£4 °C) with

poor dispersal power both in larval (cold stenother-

mal) and adult stages (reduced wings). This species

probably has a boreoalpine distribution. In Europe, it

has been recorded from the Pyrenees (Laville, 1980),

the Alps and the Tatra Mountains and in Asia from

the Hindukush Mountains (Kownacki, 1980) and far-

east Siberia (Makarchenko, 1981).

At the northernly sites, the ®rst Diamesa colonists

belonged to the zernyi/cinerella group followed by

D. latitarsis gr., D. bertrami, D. davisi gr. in Norway and

D. aberrata gr. in Svalbard. In Scandinavia, Saether

(1968) and Steffan (1971) found a similar longitudinal

Fig. 3 Longitudinal patterns of chironomid richness in ®ve

glacier-fed stream sites. The multiple points plotted at a same

distance represent the richness at each ®eld survey.



pattern to the Alps (e.g. D. lindrothi and D. valkanovi

both in the latitarsis gr and D. davisi gr., a group of

species close to D. steinboecki).

Few studies provide quantitative data on Diamesa

abundance downstream from glacial margins (Sae-

ther, 1968; Kownacki, 1991). A striking result of our

study was the abundant Diamesa populations (100±

1000 individuals m±2) even far from the snout and

even when several other invertebrates had become

abundant (Fig. 2). The Conca system was different in

that mean chironomid density (636 individuals m±2)

was low compared with the other stream systems

(except Svalbard) with a net decrease of Diamesa

species at the downstream sites. Similar densities (550

individuals m±2) were recorded by Kownacki (1991) in

South Tyrolian streams. One other difference high-

lighted by the cluster analysis was the splitting of the

Conca system into distinct upstream (C0, C1, C2) and

downstream (C3, C4, C5, C8) chironomid communi-

ties (Table 4). This re¯ected signi®cant differences in

water temperature (minimum, maximum and mean),

slope, water depth and discharge (Lencioni, 2000;

Maiolini & Lencioni, 2001).

Two others Diamesinae species were found in cold

headwaters with a mean temperature range of

0±10 °C: Pseudokiefferiella parva (in the Alps and

Fig. 4 C A N O C OC A N O C O model of the distribution of 41 chironomid taxa and six environmental variables (a) The histogram displays the

inertia accounted for by each factorial axis (b) Species abbreviations relate to full names in Appendix 1.



Fig. 5 Response curves of 13 chironomid genera/species to maximum water

temperature at ®ve glacier-fed stream sites. The log-transformed abundances are

regressed with a smoothing spline. The percentage of explained deviance is given

with the degree of signi®cance of the associated chi-square test (*P < 0.05;

**P < 0.01).



Pyrenees) and Pseudodiamesa arctica (Norway). They

have not been previously reported in kryal sites close

to glacial snouts, but have mostly been collected in

spring-fed streams where P. parva colonizes mosses

(Serra-Tosio, 1973; Kownacki, 1987; Ilg et al., 2001).

Pseudodiamesa arctica/nivosa is also characteristic of

high mountain lakes (Kownacki, 1987; Schnell &

Willassen, 1991).

The presence of Orthocladiinae species in associ-

ation with Diamesa at low temperature (<2 °C) and

very close to the snout (metakryal zone) has not been

previously documented. Eukiefferiella species and

O. rivicola gr. were the ®rst Orthocladiinae taxa

collected at mean temperature above 4 °C and about

1000 m from the snout (Saether, 1968; Kawecka et al.,

1978; Kownacki, 1991). Ward (1994) stated that in the

hypokryal (where Tmax exceeds 2 °C) other chirono-

mid genera and simuliids may occur. In our six

systems, Eukiefferiella, Orthocladius and Tvetenia spe-

cies were able to colonize the ®rst 200 m at mean

temperatures close to 0 °C. A similar pattern was

observed in glacial streams of Alaska by Milner (1994)

where an Orthocladius species was present at 2 °C.

Mountain tops may be viewed as islands in the

context of island biogeography theory (McArthur &

Wilson, 1967; Ward, 1994). Alpine streams are often

small isolated habitats compared with northern

European and arctic glacial streams originating from

extensive ice-caps. This evolutionary isolation in

combination with Ice Age refugia in the Alps (espe-

cially the south), is perceptible in the decrease of the

chironomid richness along the latitudinal gradient

although many species of Diamesinae and Orthocla-

diinae have broad geographical distribution patterns.

The successional sequence of chironomid assem-

blages along latitudinal gradients in glacial streams

follows the same pattern, with similar genera, groups

of species and species involved. Diamesa bertrami was

the most widespread species, collected in all studied

river systems, but previously recorded only on Sval-

bard in the surroundings of Ny-AÊ lesund (Serra-Tosio,

1973). These results are consistent with the trend of

colonization and successional sequence as suggested

by Milner & Petts (1994) and observed by Milner

(1994) in Alaska. These apparently predictable pat-

terns are, at least in part, a re¯ection of the harsh

physical conditions that greatly limit the numbers and

types of species that form the colonizing species pool

for glacial streams at different latitudes (Milner, 1994).

Life strategies

Chironomids of glacier-fed streams tend to display

melanism in all stages (mostly black or dark brown)

and some species of Diamesa (e.g. D. steinboecki gr.,

D. davisi gr.) have developed other strategies for cold

environments such as wing reduction, reduction in

the size of the male antennal plume and antennal ratio

and enlargement of the legs (Saether, 1968; Herrmann

et al., 1987). Brachypterous specimens (i.e. with

reduced wings) of D. steinboecki were only collected

in the Swiss Alps during this study.

Recently, the prevalence of life-cycle ¯exibility

or opportunism has been emphasized for polar

arthropods (Danks, 1999), allowing growth and

development whenever conditions are favourable.

Chironomids are one of the taxa that have devel-

oped strategies to survive the harsh conditions

prevailing in these extreme environments, such as

acceleration of the emergence and reproduction pro-

cesses, resting stages (diapause) or temperature

thresholds for developmental control (Danks &

Oliver, 1972a, b). Evidence of short life cycles was

emphasized by Serra-Tosio (1973), documenting that

in cold Alpine streams above 1800 m a.s.l., D. aberrata

and D. zernyi completed their life cycle in less than

40 days. Diamesa tonsa emerged throughout the winter

at 0 °C in an western Norwegian river (Jonsson &

Sandlund, 1975). Diamesa incallida, a krenal species,

lays eggs throughout the year and produces 8±10

generations depending on water temperature (Nolte

& Hoffmann, 1992). Experimental in situ growth

chambers used at an altitude of 2200 m in the Taillon

stream (average water temperature of 4.5 °C) demon-

strated that egg hatching to pupation of D. zernyi/

bohemani took between 39 and 54 days in June±July.

Analysis of larval head capsule widths suggested that

D. bertrami and D. latitarsis was bivoltine with emer-

gence periods in early June and August/September

(Snook, 2000).

Milner (1994) suggested that Diamesa species are

eliminated through competition with other species in

relatively stable channels, and dominate in unstable

channels because of the scarcity of competitors. In

Alaska, D. davisi was considered a fugitive species,

restricted to areas of low density of other taxa, either

because of low temperatures or frequent disturbance,

rather than being physiologically inhibited by high

temperatures (Flory & Milner, 1999). However, in



Dalelva (Norway), D. davisi gr., occurred with species

such as E. claripennis gr. at relatively high densities

(cf. Fig. 2) in unstable channels (high values of

Pfankuch's index). Similar patterns are apparent in

the longitudinal faunal gradients in the Swiss Alps

(Mutt) and in Iceland (W-JoÈkulsaÂ) for D. latitarsis gr.

and O. frigidus. It is possible that spatial or temporal

segregation may exist (e.g. hyporheic refugia, differ-

ent periods of development). Alternatively, interspec-

i®c competition may not be a key factor in these

dynamic streams.

Relationships between chironomids

and environmental factors

The Pyreneean, Alpine and Icelandic glacier-fed

streams were characterized by low chlorophyll a

concentrations in the upstream sites compared with

those recorded for Western Norway (Dalelva) and the

downstream site of Bayelva (Western Spitzbergen).

Similarly low values of algal biomass were found in

the Eastern Swiss Alps by Uehlinger, Zah, & Buergi

(1998). In Dalelva, a proglacial lake has almost been

covered by the advancing glacier. This may have

caused nutrients release from the lake sediments and

the surrounding land areas as result of erosion by ice,

thus promoting algal growth in the outlet stream.

Another characteristic that partly applies to Dalelva

but especially to Bayelva, is the closeness to the sea.

Northern and arctic areas also have a signi®cantly

longer daylength during summer. These points cou-

pled with a rather moderate channel stability index in

the upstream site, could explain the presence of the

orthoclads E. minor (1996) and E. claripennis gr.,

E. minor, Limnophyes, Tokunagaia rectangularis gr. and

Orthocladius cf. dentifer in the metakryal zone of

Dalelva during June 1997.

The conceptual model of Milner & Petts (1994)

relates zoobenthic gradients to water temperature and

geomorphological instability, as a function of distance

from the glacial margins. The present study examined

chironomid distributions in relation to geomorpho-

logical and physico-chemical variables and provided

further documentation bearing on the conceptual

model. Fig. 6 summarizes this longitudinal distribu-

tion of key chironomid of the kryal zone of glacier-fed

streams taxa in relation with maximum water tem-

perature. Diamesa species were predicted to decrease

when maximum temperature exceeded 4 °C where

channel stability increased. In the European glacial-

fed streams studied, Diamesa maintained abundant

populations in warmer environments (Tmax 6 15 °C).

Fig. 6 Schematic representation of longitudinal succession of characteristic chironomid taxa in relation to water temperature and

distance from snout in six European glacier-fed streams (Pyrenees to Svalbard).



Other Diamesinae (Pseudokiefferiella parva, Pseudodia-

mesa arctica) and the orthoclad species E. minor/®ttkaui

were also able to colonize the metakryal zone

(Tmax 6 2 °C) in the ®rst 100 m from the glacier.

The orthoclads Eukiefferiella claripennis gr., O. frigidus,

O. rivicola gr. and Tvetenia came later downstream at

Tmax > 2 °C.

Algal ®laments such as diatoms and the chryso-

phyte Hydrurus foetidus (Vill.), common in the Alps

and Northern Scandinavia (Ward, 1994; Kawecka et al.,

1978; Lods-Crozet et al., 2001; Maiolini & Lencioni,

2001) provide resources and protection (low shear

stress) from currents and abrasive sediments and can

play a role as refugia for Diamesinae and Orthocladii-

nae in the upper reaches of glacial streams (Fig. 7).

Modi®ers to the conceptual model such as pro-

glacial lakes that reduce turbidity and increased

temperature, channel stability and nutrients induced

a shift in the sequence of occurrence of the chirono-

mid taxa as predicted by Milner & Petts (1994). This

was illustrated in the river Dalelva (Western Norway).

Another predicted in¯uence is the effect of tributaries.

This impact can be very different depending on their

size and discharge, their hydrological origin (snow-

melt, spring-fed or glacial melt) and the distance from

the source. Examples from the Swiss Alps and

western Norway from small snowmelt tributaries

indicate a minor contribution to the main channel

benthos (Petts & Bickerton, 1994; Haug, Salveit &

Brittain, 2001; Ilg et al., 2001).

In conclusion, despite very harsh conditions (low

temperature, narrow thermal heterogeneity, high

turbidity and high channel instability), glacial streams

support a relatively rich chironomid community

(a total of 63 taxa in the six streams studied) with

increasing densities and diversity downstream of the

glacier snout as predicted by Milner & Petts (1994).

Nevertheless, chironomid richness reaches 150 species

if all the headwaters (glacial meltwater, snowmelt and

spring-fed stream) are considered (Brittain et al.,

2001b). This represents about 15% of the total number

of species of Chironomidae known from Europe

(Ashe & Cranston, 1990). In addition, a wider

geographical and ecological distribution of several

species has been documented in relation to previous

studies. Future studies, should also address the need

for progress in chironomid taxonomy. Keys for the

genus Diamesa, are a prerequisite for a better under-

standing of chironomid community dynamics in

glacial headwaters.

Acknowledgments

The project, Arctic and Alpine Stream Ecosystem

Research (AASER) was supported by the European

Commission (No ENV-CT95-0164) and the Swiss

Federal Of®ce for Education and Science. We

are grateful to G.A. Halvorsen, P. Langton and

E. Willassen for their advice on chironomid taxon-

omy. The authors thank also A.M. Milner and an

anonymous reviewer for helpful comments on an

early version of the manuscript.

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Appendix 1 Chironomidae species composition and mean abundance (expressed in classes) of in the six glacial stream

Code Taxa TAI CON MUT BRI WJO BAY

Concind Conchapelopia sp. 2

Macrind Macropelopia sp. + 1

Zavrind Zavrelimyia sp. 3

Boreind Boreoheptagyia 2 2

Diamgabe Diamesa aberrata gr. + 2 2

Diam ber Diamesa bertrami Edwards + 3 2 4 4

Diamgdam Diamesa damp® gr. 2

Diamgdav Diamesa davisi gr. 4

Diamglat Diamesa latitarsis gr. + 3 5 4 4

Diam ste Diamesa steinboecki Goetgh. 4 3

Diamgzer Diamesa zernyi gr./cinerella gr. + 4 4 4 4 4

DiamgA Diamesa gr. A(*) + 4 5 3 4

Pseu arc Pseudodiamesa arctica (Mall.) 3

Pseu bra Pseudodiamesa branickii (Now.) + 3 2

Pseu par Pseudodiefferiella parva (Edwards) + 3 3

Syndind Syndiamesa sp. 2 2

sfdiame Diamesinae unidenti®ed (*) + 2 4 2



Appendix 1 (Continued)

Code Taxa TAI CON MUT BRI WJO BAY

Bril bif Brillia bi®da (Meigen) 2 2

Bryoind Bryophaenocladius spp. 1

Chaegden Chaetocladius dentiforceps gr. 1 2 2 2

Chaegpig Chaetocladius piger gr. 3 2 3 2 2

Coryind Corynoneura spp. + 2 2 3

Cricgbin Cricotopus bicinctus gr. 2

Cricgfus Cricotopus fuscus gr./tibialis gr. 1 2 2 2

Cricgsyl Cricotopus sylvestris gr. 2

Cricgtre Cricotopus tremulus gr. 2

Euki bre Eukiefferiella brevicalcar (Kieff.)/tirolensis Goetgh. 3 2 3

Eukitgcla Eukiefferiella claripennis gr. + 3 2 3 4

Eukicoe Eukiefferiella coerulescens (Kieff. in Zavrel) 2

Eukicya Eukiefferiella cyanea Thien. + 2

Eukigdev Eukiefferiella devonica gr. 2 3

Euki min Eukiefferiella minor (Edw.)/®ttkaui Lehm. 2 2 3 4

Heteind Heleniella spp. + 3 2

Heteind Heterotrissocladius spp. 2 2 2

Hetoind Heterotanytarsus sp. +

Krenind Krenosmittia spp. + 3 2

Limnind Limnophyes sp. 2

Metrind Metriocnemus sp. + 1 2

Orth fus Orthocladius (E.) fuscimanus (K. in Kieff. & Thien.) 2

Orth lut Orthocladius (E.) luteipes Goetgh. 3

Orthgriv Orthocladius (E.) rivicola gr. + 3 3

Orth fri Orthocladius (O.) frigidus (Zetter.) + 2 3 2 4

Orth obl Orthocladius (O.) oblidens (Walk.) 3

Orth con Orthocladius (P.) consobrinus (Holm.) 1

Orthind Orthocladius spp. + 3 2 2

Para gra Parakiefferiella cf. gracillima (Kieff.) 2

Para sty Parametriocnemus stylatus Kieff. + 3 2

Paraind Paraphaenocladius spp. 2

Para ruf Paratrichocladius ru®ventris (Meig.) 2

Para ski Paratrichocladius skirwitensis (Edw.) 1

Paro nud Parorthocladius nudipennis (K. in Kieff. & Thien.) + 2 2

Psecind Psectrocladius sp. 2

Pseuind Pseudosmittia sp. 2

Rheo eff Rheocricotopus effusus (Walk.) + 3 2

Smitind Smittia sp. 1 3

Thieind Thienemannia spp. 2

Thilind Thienemanniella spp. + 2 3

Tokugind Tokunagaia rectangularis gr. 2 3

Tvetind Tvetenia calvescens (Edw.) + bavarica (Goetgh.) + 3 2 2

sfortho Orthocladiinae unidenti®ed (*) + 3 2 3 2

Parcind Paracladopelma sp. 1

Polyind Polypedilum sp. 1

Micr atr Micropsectra atrofasciata (Kieff.) 4 3

Micrind Micropsectra spp. + 2

Rheoind Rheotanytarsus sp. +

Stemind Stempellinella sp. +

Taxonomic richness 27 42 29 20 20 7

*Taxa not counted in taxonomic richness.

+: No quantitative data; 1: <1.0; 2: 1.0±10; 3: 10.1±100; 4: 100.1±1000; 5: >1000 individuals m)2.



Chironomid (Diptera: Chironomidae) communities in six European glacier-fed streams

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