Temporal and spatial distribution of planktic cyanobacteria in Lake Kastoria, Greece, a shallow, urban lake

The temporal and spatial distribution of planktic cyanobacteria and some environmental parameters were studied in the shallow, urban Lake Kastoria, Greece from June 1996 to June 1997. Water temperature varied from 6–27 °C, pH from 7.5–8.9 and dissolved O₂ concentration from 0.7–12 mg m^-3 10^-3. The mean annual Chl a concentration was 83 mg Chl a m^-3 indicative of the eutrophic-hypertrophic state of the lake. Cyanobacterial biomass ranged from 11–238 g FW m^-3, constituting about 90% of the total phytoplankton biomass throughout the year. Cyanobacterial biomass was non-uniformly distributed both vertically and horizontally from August to November 1996 and resulted mainly from the distribution of Microcystis. Seven cyanobacterial taxa were reported for the first time in Lake Kastoria. Six taxa were dominant: Microcystis aeruginosa, M. flos-aquae, M. novacekii. Limnothrix redekei, Anabaena sp. and Cylindrospermopsis raciborskii. The dominant cyanobacterial taxa can be grouped on the basis of their distribution patterns (1) Microcystis species: maximum biomass occurring at pH > 8, temperature 12–17 °C, depth < 0.2 m; (2) Anabaena sp. and Cylindrospermopsis raciborskii : maximum biomass at temperatures 23–26 °C; (3) Limnothrix redekei : maximum biomass at temperatures 6–27 °C. Usually, non-uniform, vertical distributions of cyanobacterial biomass were associated with the formation of temperature, pH and O₂ gradients. L. redekei was considered to be a key lake organism since it contributed up to 59% of the cyanobacterial biomass. Interestingly, three of the dominant cyanobacteria Microcystis aeruginosa, Anabaena sp. and Cylindrospermopsis raciborskii belong to genera that include toxin-producing species.     

Species composition and seasonal cycles of phytoplankton with special reference to the nanoplankton of Lake Mikri Prespa

The phytoplankton of Lake Mikri Prespa was studied atmonthly or biweekly intervals during the period May1990–September 1992. Its species composition,consisting of a great number of cyanophytes and a verysmall number of chrysophytes and desmids, may reflectthe eutrophic character of the lake. Moreover, themean annual biomass values (15.0 and 3.2 g m^–3 inthe two years, respectively) and the maximum biomass(38.1, 6.4 and 9.6 g m^–3), classify Mikri Prespaas a eutrophic lake. A tendency towards adouble-peaked pattern of biomass distribution in timewith one peak in autumn, composed mainly ofcyanophytes, and another in spring made up of diatoms,was observed. This pattern contrasts with the standardpattern in eutrophic, stratified temperate lakes,which exhibit a third biomass maximum in summer.Cyanophytes were the most important group in terms ofbiomass and were dominated by the species Microcystis aeruginosa, Microcystis wesenbergii,Anabaena lemmermannii var. minor and Aphanocapsa elachista var. conferta. Diatomsconstituted the second most important group, with main representative the species Cyclotellaocellata. Cyanophytes, diatoms, chlorophytes anddinophytes revealed annual periodicity whereas theother algal groups did not show any seasonality atall.The nanoplankton constituted an important part ofalgal biomass (38.9 and 49.9% in the two years,respectively) and revealed annual periodicity withmaximum values in winter and spring, mainly composedof diatoms and cryptophytes. Low temperature,increased rainfall and high DIN concentrations seemedto be the main factors influencing the seasonality.Although the percentage contribution of nanoplanktondecreased with the increase in total biomass,justifying the classification of Lake Mikri Prespaamong the eutrophic lakes, the nanoplankton biomassdid not correlate significantly with totalphytoplankton biomass.     

Winter Ciliates in a British Columbian Fjord: Six New Species and an Analysis of Ciliate Putative Prey

ABSTRACT. This work provides the first study of North Pacific planktonic ciliates by quantitative protargol staining. Triplicate water bottle samples were collected at a depth of 2 m (above the shallow pycnocline) at six stations in Indian Arm, British Columbia, on February 15, 1990, and February 26, 1991. Thirty-six ciliate species were observed. Six new species are described from protargolstained specimens: Strombidium lynni n. sp., Strombidium taylori n. sp., Strombidium basimorphum n. sp., Slrombidiurn ventropinnum n. sp., Strobilidium undinum n. sp., and Urotricha cyrtonucleata n. sp.
Ciliate abundance varied significantly (ANOVA, α= 0.05) between sampling sites, ranging from 550 to 6,800 cells/liter in 1990 and from 1,800 to 7,900 cells/liter in 1991. Biomass also varied significantly (ANOVA, α= 0.05) ranging from 3.7 × 10⁵ to 3.3 × 10⁶ pg carbon/liter in 1990 and 3.04 × 10⁶− 6.97 × 10⁶ pg carbon/liter in 1991. Putative prey were enumerated in three size fractions (1.5–5 μm, 5–10 μm and 10–25 μm). The source of variation in ciliate abundance and biomass was not identified. Parameters of salinity, temperature, putative prey, chlorophyll a and pycnocline depth did not significantly correlate with ciliate biomass or abundance (α= 0.05).     

Microbial and classical food webs: A visit to a hypertrophic lake

Abstract: Plankton community structure and fluxes of carbon for bacteria (production and bacterivory) were investigated in the urban, hypertrophic Lake Rodó (Uruguay) using a short time interval for sampling (5–15 d) during one year. The lake sustains a high phytoplankton biomass (up to 335 μg l⁻¹ chlorophyll a ) always dominated by the filamentous cyanobacteria Planktothrix agardhii . The zooplankton community was numerically dominated by rotifers and ciliates; cladocerans were rare during most of the year. The rotifer abundance was very high (up to 10⁵ individual l⁻¹), the bacterivorous Anuraeopsis fissa being the most abundant species. Predation rates of heterotrophic nanoflagellates (HNF) on bacteria (range: 31–130 bacteria HNF⁻¹ h⁻¹) were higher than those reported in the literature for field studies. A carbon budget showed that HNF can consume on average 91 and 76% of the bacterial carbon production in summer and winter, respectively. Bacterial turnover times are the lowest reported until now from field conditions (5 to 42 h). Consequently, bacterial carbon production was extremely high (72 to 1071 μg C l⁻¹ d⁻¹). Bacterial production was positively correlated to bacterial abundance but the relationship was significantly improved by the inclusion of temperature (82% variability explained). My results support the general trend for increased bacterial production with increasing trophic status, and suggest a lower energy transfer efficiency to higher trophic levels in hypertrophic lakes due to the many trophic interactions involved.     

Effects of SO2 on photosynthesis and ribulose bisphosphate carboxylase in pine tree seedlings

Fumigations of 4–7 week old seelings of Pinus silvestris , with ca 400 μg SO₂ m^-3 for 4–5 days resulted in a decrease both in net photosynthetic rate and in the levels of ribulose bisphosphate carboxylase activity of the primary needles. The effect on net photosynthesis was reversible. No visible damages were observed on the needles. Lower concentrations, ca 200 μg SO₂ m^-3, for ca 6 days inhibited net photosynthesis reversibly. The effect on net photosynthesis was not the result of stomata closure or of increased respiration. A dose-response relation for the inhibition of net photosynthesis and ribulose bisphosphate carboxylase is suggested. A similar relation was observed for the chlorophyll content of the needles. The reversible inhibition of photosynthesis was evident only at high quantum flux density, and the quantum yield of photosynthesis at rate limiting quantum flux was not affected. This was also suggested from an experiment with Scots pine in the field.     

LIGHT-DEPENDENT GROWTH, DARK SURVIVAL, AND GLUCOSE UPTAKE BY CRYPTOPHYTES ISOLATED FROM A FRESHWATER CHEMOCLINE

Clones of Cryptomonas phaseolus Skuja , Cryptomonas rostratiformis ( Skuja ) Skuja in Huber-Pestalozi, and Cryptomonas undulata Gervais were isolated from the deep chlorophyll maximum near the oxic/anoxic boundary layer of the mesoeutrophic lake Schlachtensee, Germany. Different autecological features of these species were studied in batch culture experiments . Cryptomonas cf . ovata Ehrenberg and Chroomonas sp. that never dominated in the deep chlorophyll layer were also isolated from Schlachtensee to study their light-dependent growth in comparison to the deep-living species . Cryptomonas undulata, C. cf . ovata, and C. phaseolus had a very low light compensation point ( 5–7 μmol.m^-2.s^-1 ), whereas the growth rate of Chroomonas sp. and C. rostratiformis was positive above 16 and 24 μmol.m^-2.s^-1 . Cryptomonas phaseclus and Chroomonas sp. became photoinhibited above photon flux densities of 92 and 116 μmol.m^-2.s^-1 . Cryptomonas rostratiformis, C. cf . ovata, and C. undulata reached a maximum growth rate at a considerably higher photon flux density (198–250 μmol.m^-2.s^-1 ). Cryptomonas phaseolus grew fastest under light-limiting conditions . Chyptomonas phaseolus and C. undulata were best able to suruive prolonged periods of darkness . Cryptomonas phaseolus, C. rostratiformis, and C. undulata did not show any uptake of fluorescent latex beads. When labeled glucose was provided in naturally occurring concentrations, carbon uptake by C. phaseolus, C. rostratiformis, and C. undulata was negligibly small in comparison to cellular carbon content. I suggest that the adaptation to a low-light environment is an important preadaptation for the dominance of C. phaseolus and C. undulata near the freshwater chemocline .     

Life cycle, production, microdistribution and diet of the damselfly Euphaea decorata (Odonata: Euphaeidae) in a Hong Kong forest stream

Euphaea decorata in Tai Po Kau Forest Stream (Hong Kong) was univoltine. Most recruitment took place in summer, and larval growth proceeded throughout the year. Life-cycles recorded in 1977–78 and 1978–79 were similar. Annual production estimates, using the removal-summation, instantaneous growth and size-frequency methods, were more similar for the 1978–79 generation (ranging from 158.7–174.7; mean 1671 mg dry wt m^-2) than for the 1977–78 generation (93.9-173-6; mean 131.7 mg dry wt m^-2). Mean biomass was similar for both generations (ranging from 33.5–33.9 mg dry wt m^-2), and mean P/B ratios were 3.9 1977–78) and 5.0 (1978–79). These are the first estimates of annual production by an Oriental stream insect.
Larvae were most abundant at microsites in the middle of the stream. Multiple regression analysis indicated that substratum characteristics were a major determinant of microdistribution. Euphaea decorata apparently favoured poorly-sorted sediments with highly peaked grain size-frequency distributions, containing few fine particles.
The carnivorous larvae showed ontogenetic changes in diet. Small individuals consumed mainly chironomid (Diptera) larvae; the diet expanded to include (successively) larvae of Ephemeroptera and Trichoptera as E. decorata grew. Seasonal changes in diet were also apparent, although larval diets during spring and summer were similar. There was also considerable overlap between autumn and winter diets. Ontogenetic influences upon prey consumed were not sufficient to account for the observed seasonal differences.     

Seasonal changes in biom ass of macrophytes on shaded and unshaded sections of the River Lambourn, England

SUMMARY. Monthly changes in the biomass of Ranunculus, Berula and Callitriche were recorded on two 50-m sites on the River Lambourn at Bagnor between March 1971 and October 1973. On the unshaded site. Ranunculus was the dominant macrophyte and characteristically its biomass changed from 20–40 g dry wt m^-2 in March to around 400 g dry wt m^-2 at the end of the growing season. On the shaded site, where Berula was the dominant macrophyte. the biomass of Ranunculus was lower than on the unshaded site. There was no significant difference between the mean biomasses of Berula on these two sites but Callitriche had a signifieantly higher biomass on the shaded site. Estimates of the total biomass of macrophyte on each site were calculated and the biomass of macrophyte removed during cutting operations each summer was also assessed.     

The content of prostaglandins and their precursors in Mortierella and Cunninghamella species

Five strains of filamentous fungi belonging to the genera Mortierella and Cunninghamella were examined for the content of dihomo-γ-linolenic, arachidonic, eicosapentaenoic acids and prostaglandins (type E₂ and F _2α). Prostaglandins were detected using an ELISA method in mycelia of all tested strains (range 50–4800 ng g⁻¹ of PGE₂ and 6–30 ng g⁻¹ of PG F _2α). Several micro-organisms also produced prostaglandins in the culture medium (2·2–137·6 μg l⁻¹ for PGE₂ and 0·4–7·8 μg l⁻¹ for PG F _2α).     

The growth rate of eel in tributaries of the lower River Severn, England, and its relationship with stock size

The growth rate of 1980 eel Anguilla anguilla from 15 sites in the Severn system varied between 16·4 and 27·9 mm year^-1, density from 0·12 to 1·14 m^-2 and biomass from 2·56 to 25·24 g m^-2. There was no significant relationship between growth rate and density or biomass ( P > 0·05).     

A limnological investigation of the tarn Syslaktjønn, W Norway

An investigation covering hydrography, chemistry, vascular and cryptogamic plants, nitrogen fixation, phytoplankton biomass and production, and zooplankton was carried out from April to November 1976 in tarn in W Norway, The volume of the tarn was 18000 m³ and the turnover time about 30 d. Temperature ranged between 3.6 and 23.4°C and pH between 4.8 and 5.5. Nuphar luteum and Carex rostrata were the two dominating vasculars-with biomasses of 117 and 97 g m⁻², respectively The biomass of the bryophytes ( Sphagnum spp.) was about 510 g m⁻² and the production of the order 0.2–2.1 μg (mg d.w.)⁻¹h⁻¹. Nitrogen fixation in association with Sphagnum spp. was estimated at 25 g yr⁻¹ for the whole tarn. Phytoplankton was dominated by diatoms, green algae and chrysophyceans. The chlorophyll a content ranged from 2 to 20 mg m⁻³ and the carbon assimilation rates from 0.03 to 20 mg C m⁻³h⁻¹ at 0–4 m depths. Production in the period was of the magnitude 22 g C m⁻². The copepod Eudiaptomus gracilis was the most common netzooplankter. Large numbers of rotationrians were found during summer.     

Potassium dependence and phytoplankton ecology: an experimental study

SUMMARY 1. Unialgal cultures of three species common in the freshwater phytoplankton were used to test limitation of specific growth rate and final yield in defined media of low K⁺ concentration (range <0.3–6 μmol L⁻¹ or mmol m⁻³).
2. Growth rate of the diatom Asterionella formosa was independent of K⁺ concentration above 0.7 μmol L⁻¹. Final yield was dependent on initial concentration when accompanied by K⁺ depletion below this concentration, but not by lesser depletion with more residual K⁺. Analyses of particulate K in the biomass indicated a mean final cell content of 2.8 μmol K 10⁻⁸ cells, approximately 1.0% of the organic dry weight.
3. Less detailed work with the diatom Diatoma elongatum showed no dependence of growth rate or final yield upon the initial K⁺ concentration in the range 0.8–3.2 μmol L⁻¹. The phytoflagellate Plagioselmis nannoplanctica suffered net mortality in the lowest concentration tested, 0.8 μmol L⁻¹.
4. Comparison with the range of K⁺ concentration in natural fresh waters, including a depletion induced by an aquatic macrophyte, suggests that K⁺ is unlikely to limit growth of phytoplankton. Nevertheless, there can be correlation of K⁺ with lake trophy.     

Seasonality and spatial variation in abundance, biomass and activity of heterotrophic bacterioplankton in relation to some biotic and abiotic variables in an Ethiopian rift-valley lake (Awassa)

SUMMARY. I. Seasonality and spatial variation in abundance, biomass and activity of heterotrophic bacterioplankton was studied in a tropical freshwater lake. Variation in phytoplankton biomass and production, and several other limnological parameters, were also quantified.
2. Bacterial number and biomass fluctuated between 3.88–8.33×10⁶ ml⁻¹ and 68–125 mg C m⁻³, respectively. No spatial variation was observed in these bacterial variables, although other limnological parameters showed vertical variation.
3. Seasonal and vertical variation of heterotrophic bacterial activity were estimated from oxygen consumption, ¹⁴CO₂dark uptake and plate counts of colony forming units. All three methods showed vertical heterogeneity, with higher activity in the hypolimnion during the long stratification period (February May). Oxygen consumption rate and plate counts showed seasonality.
4. In spite of the low seasonality of climate in the tropics, several biological, chemical and physical variables were correlated with changes in bacterial variables. Wind and rainfall, and their effects on stratification and mixing, vertical distribution of nutrients and rate of primary production appeared to be the important parameters affecting heterotrophic bacterioplankton.     

Effects of light and temperature on the cell size and some biochemical components in two freshwater cryptophytes

The effects of light and temperature on cell size and cellular composition (chlorophyll, protein, carbohydrate) of two freshwater cryptophytes were studied with batch cultures. Neither of the species had a constant cell size but the size varied with growth conditions. At each temperature the smallest cells were recorded at the lowest experimental photon flux density. The smallest cells of Cryptomonas 979/67 had an average volume of 232 μm³ and the largest ones 1 020 μm³. In Cryptomonas 979/62 the smallest and largest cells measured 4 306 μm³ and 12 450 μm³. Both species increased their cellular chlorophyll content when PFB dropped below 110–120 μmol m^-2 s^-1. The highest and lowest chlorophyll contents of 979/67 were 7.45 fg μm^-3 and 0.55 fg μm^-2 respectively. For 979/62 the corresponding values were 10.23 fg μm^-3 and 0.93 fg μm^-3. In both species the protein content remained stable at PFDs higher than 110–120 μmol m^-2 S^-1. The highest content of protein measured in 979/67 was 638 fg μm^-3 and the lowest 147 fg μm^-3. For 979/62 these values were 1 036 fg μm^-3 and 148 fg μm^-3 respectively. The carbohydrate results were less clear and no pattern either in response to photon flux density or temperature was obvious. The lowest and highest contents recorded for 979/67 were 62 fg μm^-3 and 409 fg μ^-3 and for 979162, 36 fg μm^-3 and 329 fg μm^-3     

Life cycle and population dynamics of Trochosa terricola Thorell (Araneae: Lycosidae) in a Norfolk grass heath

Abstract. 1. The population of the lycosid Trochosa terricola Thorell was sampled from April 1973 to August 1975 at Weeting Heath NNR, a Breckland grass heath.
2. Four sampling methods were compared for efficiency. Hand searching gave density estimates between 38.3 and 70.1% of heat extraction.
3. The temperature range in the sward at +1 cm was –5°C to 39°C with January and July means of 3.2°C and 17.4°C.
4. Eight male and nine female instars were determined and the life cycle extended over 2 or 3 years.
5. Adults were nocturnal but the juveniles diurnal. An annual diplochrone activity pattern was observed for adult males.
6. The horizontal distribution within the sward was aggregated, the structure and microhabitat being important determining factors. The population density was greater in moist, young Festuca spp. tussocks. An equation relating population density to habitat characteristics was derived.
7. The overall population density ranged from 14.0 m^-2 to 76.0 m^-2 and was maximal in autumn after breeding. The population biomass was greatest during autumn (291.2 mg d.wt m^-2).
8. Mean number of juveniles emerging from an egg sac was 77.3 (first sac) and 38.0 (second sac). The natality in 1973 was 66.8 individuals m^-2.
9. The survivorship curve until maturity varied between types I and III in different years.
10. The population dynamics were compared and are discussed in the light of other data. The variable population characteristics suggested that Den Boer's "spreading of risk" theory applied to the T.terricola population.     

Phytoplankton and pelagic primary productivity in Øvre Heimdalsvatn

A phytoplankton investigation was carried out in the subalpine, low-productive Norwegian lake Øvre Heimdalsvatn in 1969–70 and 1972. This paper describes the temporal and spatial distribution of the standing stock of phytoplankton, and phytoplankton primary productivity. The annual average primary productivity in 1972 was 4.0–4.9 mg C m⁻³ d⁻¹; the annual average standing stock varied from 120 mg m⁻³ (freshweight) in 1969–70, to 250 mg m⁻³ in 1972. Phytoplankton species composition and size distribution is discussed. Throughout the year the phytoplankton is dominated by small (ultraplankton) species; μ-algae (< 5 μm) showed cell concentrations up to 15 mill. cells 1⁻¹. The dominating group was chrysophytes; cryptophytes, dinoflagellates or green algae were at times abundant. A phytoplankton monthly budget and a diagram showing annual average carbon flow through the standing stock of phytoplankton are presented; the phytoplankton dynamics in Øvre Heimdalsvatn is compared to that of other low-productive lakes.     

Inorganic carbon limitation of photosynthesis in lake phytoplankton

1. Inorganic carbon availability influences species composition of phytoplankton in acidic and highly alkaline lakes, whereas the overall influence on community photosynthesis and growth is subject to debate.
2. The influence of total dissolved inorganic carbon (DIC) and free CO₂ on community photosynthesis was studied in six Danish lakes during the summer of 1995. The lakes were selected to ensure a wide range of chlorophyll a concentrations (1–120 μg l^–1), pH (5.6–9.6) and DIC concentration (0.02–2.5 m m ). Photosynthesis experiments were performed using the ¹⁴C technique in CO₂-manipulated water samples, either by changing the pH or by adding/removing CO₂.
3. Lake waters were naturally CO₂ supersaturated during most of the experimental period and inorganic carbon limitation of photosynthetic rates did not occur under ambient conditions. However, photosynthesis by phytoplankton in lakes with low and intermediate DIC concentrations was seriously restricted when CO₂ concentrations declined. Similarly, photosynthesis was limited by low CO₂ concentrations during phytoplankton blooms in the hardwater alkaline lakes.     

A modified drop-net method for sampling mobile epifauna on marine shallow sandy bottoms

The seasonal variations in numbers and biomass of the mobile epifauna of a shallow, sandy bay in Gullmar Fjord (Sweden) was investigated during 1976–1977 using the drop-net technique. Juvenile plaice, Pleuronectes platessa L., sand goby, Pomatoschistus minutus (Pallas), and brown shrimp Crangon crangon L. are the dominant epifaunal species. A net enclosing an area of 100 m² was used, and the organisms captured were collected with a small trawl. Three stations with a water depth≤ 1 m were regularly sampled with a total number of 73 drops. Maximum abundance was for plaice in June (6 ind m^-2), for the shrimp in July-August (61 ind m^-2), and for sand goby in September (2 ind m^-2). Standing stocks (dry wt) were 0.2, 1.5 and 0.2 g m^-2 respectively. Production estimates were based on seasonal changes in size frequency and information on specific growth rates. The production rate was for plaice (0-group) 0.3 g m^-2 yr^-1, for the shrimp 1.5, and for sand goby 0.2 g m^-2 yr^-1. Reliable estimates of the absolute abundance can be derived from the mean catch per unit area only when the efficiency of the fishing gear is known. After 6 hauls with the trawl in the drop-net enclosure more than 85% of the shrimps were caught and after the fifteenth haul less than 1% were still left. The fishing efficiency of a push-net in relation to the drop-net was for the shrimp 50%, for plaice 35% and for sand goby 17%.     

Extracellular release of photosynthetic products by freshwater phytoplankton populations, with special reference to the algal species involved

SUMMARY. Over three successive years, depth profiles of C-fixation and excretion, chlorophyll- a concentrations, phytoplankton species composition and bacterial numbers were determined in Lake Vechten, a slightly eutrophic lake in The Netherlands. Special attention was given to the method used to measure extracellular release.
Excretion of dissolved organic ¹⁴C depended largely upon the photo-synthetic activity of the phytoplankton, ranging from 0–2.5 mg m^-1 h^-1, representing a percentage extracellular release (PER) of 0–25%.
During a period in August, however, a subsurface chlorophyll- a maximum at 5–7 m depth coincided with high excretion rates of up to 10 mg Cm^-3 h^-1 (PER = 55%). Phytoplankton analysis revealed a stratification in numbers of Mallomonas caudata with a maximum at 5–7 m depth.
The results suggest that in these water layers bacterial populations grew at the expense of the dissolved organic carbon compounds excreted by Mallomonas caudata. This means that extracellular release can temporarily function as an important nutrient source for the heterotrophie community in addition to the more or less constant dissolved organic carbon pool.     

Spatio-temporal variation in macroinvertebrate assemblages of glacial streams in the Swiss Alps

1. Changes in water chemistry, benthic organic matter (BOM), and macroinvertebrates were examined in four different glacial streams over an annual cycle. The streams experienced strong seasonal changes in water chemistry that reflected temporal changes in the influence from the source glacier, especially in water turbidity, particulate phosphorus and conductivity.
2. Nitrogen concentrations were high (nitrate-N values were 130–274 μg L^–1), especially during spring snowmelt runoff. Benthic organic matter attained >600 g m^–2 dry mass at certain times, peaks being associated with seasonal blooms of the alga Hydrurus foetidus .
3. Macroinvertebrate taxon richness was two to three times higher (also numbers and biomass) in winter than summer suggesting winter may be a more favourable period for these animals. Benthic densities averaged 1140–3820 ind. m^–2, although peaking as high as 9000 ind. m^–2. Average annual biomass ranged from 102 to 721 mg m^–2, and reached >2000 mg m^–2 at one site in autumn.
4. Taxa common to all sites included the dipterans Diamesa spp. and Rhypholophus sp., the plecopterans Leuctra spp. and Rhabdiopteryx alpina , and the ephemeropterans Baetis alpinus and Rhithrogena spp. Principal components analysis clearly separated winter assemblages from those found in summer.