Zooplankton,and related phytoplankton cycles,in a eutrophic lake

The seasonal cycles of zooplankton were determined for 18 consecutive months in a sewage-enriched lake in northern Canada and were related to algal availability and utilization, food consumption, temperature and the density of predators. Most of the common species (Daphnia pulex, Daphnia middenorffiana, Keratella cochlearis, Keratella quadrata, Polyarthra vulgaris) increased in abundance in May and June, reached a mid-summer maximum, and declined sharply in the fall. Phytoplankton densities increased sharply in May, peaked early in June and gradually decreased through the summer and fall. Since the quantity of algae in the guts remained constant during this period, algal availability and utilization had no direct impact on the seasonal cycles of any species. Furthermore, the amount of ingested material in D. pulex and D. middendorffiana was similar regardless of time of year, implying that the total quantity of food in the environment did not restrict development. Although temperature was the most important factor influencing variations in the densities of all species, predation by Cyclops spp. probably had little effect on the population dynamics of the fauna.     

The impact of pH on interactions among phytoplankton algae, zooplankton and perch (Perca fluviatilis) in a shallow, fertile lake

1. The combined effects of increasing pH (< 9–11) and increasing densities of perch (0, two, four per enclosure) have been investigated in polyethylene enclosures of volume about 1100 1 in a shallow, fertile lake in Cheshire. 2. Increasing pH decreased carbon dioxide concentrations, chlorophyll a concentrations and diatom biomass. It led to increases in the proportions of Cryptophyta (to pH 10) and Chlorophyta (to pH 11). Although ample inocula were present, significant growths of cyanophytes were not recorded, contrary to expectation. 3. Increasing pH led to increases in numbers of Daphnia hyalina particularly at pH 10 but collapse at pH 11. This persistence at pH 10, independent of perch number, is attributed to reduced feeding of the fish, which survived at this pH. Other zooplankters (Ceriodaphnia spp., Bosmina longirostris, Polyphemus pediculus, Cyclops spp.) all declined with increasing pH. 4. Increasing fish density resulted in an increase in chlorophyll a concentration and in the biomass of Chlorophyta but had no effect on cyanophyte or cryptophyte biomass. 5. Increasing fish density led to declines in Daphnia in the untreated lake-water controls (pH < 9) and at pH 9, but had no effect at pH 10 where Daphnia hyalina was very abundant. Numbers of Ceriodaphnia spp. and Bosmina longirostris increased with increasing fish density, whilst numbers of Polyphemus pediculus and Cyclops spp. were independent of it. 6. The results are discussed in the light of contemporary knowledge of the factors resulting in large cyanophyte growths and of the factors controlling the stability of macrophyte-dominated and phytoplankton-dominated states in shallow lakes. The interaction between pH and fish density and consequent non-linear response of Daphnia hyalina is particularly notable because of the significance of zooplankton grazing in shallow lakes.     

Net heterotrophy in Faroe Islands clear-water lakes: causes and consequences for bacterioplankton and phytoplankton

1. Five oligotrophic clear‐water lakes on the Faroe Islands were studied during August 2000. Algal and bacterial production rates, community respiration, and CO₂ saturation were determined. In addition, we examined the plankton community composition (phytoplankton and heterotrophic nanoflagellates) and measured the grazing pressure exerted by common mixotrophic species on bacteria. 2. High respiration to primary production (6.6–33.2) and supersaturation of CO₂ (830–2140 μatm) implied that the lakes were net heterotrophic and that the pelagic heterotrophic plankton were subsidised by allochthonous organic carbon. However, in spite of the apparent high level of net heterotrophy, primary production exceeded bacterial production and the food base for higher trophic levels appeared to be mainly autotrophic. 3. We suggest that the observed net heterotrophy in these lakes was a result of the oligotrophic conditions and hence low primary production in combination with an input of allochthonous C with a relatively high availability. 4. Mixotrophic phytoplankton (Cryptomonas spp., Dinobryon spp. and flagellates cf. Ochromonas spp.) constituted a large percentage of the plankton community (17–83%), possibly as a result of their capacity to exploit bacteria as a means of acquiring nutrients in these nutrient poor systems.     

Some factors influencing the density of subarctic populations of Bosmina longirostris,Holopedium gibberum,Codonella cratera and Ceratium hirundinella

Changes in the density of 2 populations of Bosmina longirostris, Holopedium gibberum and Codonella cratera were correlated through multiple regression analyses with shifts in temperature, light, nannoplankton densities and seston weight. Sampling took place every 2 weeks between June 1975 and November 1976 in the Yellowknife River and Yellowknife Bay, both in the Canadian subarctic. Temperature was usually the main factor influencing all 3 species, accounting for up to 60% of the seasonal variability in B. longirostris, 37% in H. gibberum and 62% in Codonella cratera. Seston (the major food source) ranked second overall and in one instance accounted for 60% of density changes in B. longirostris. Nannoplankton were consumed in only small numbers and had little influence on densities. Light was of minor importance to all species. Temperature was also the main factor effecting reproduction and feeding in B. longirostris and H. gibberum (the only species studied). The simultaneous collections of Ceratium hirundinella made in the river and bay indicated that temperature accounted for 30–55% of the seasonal variability of this species, followed by light (4% and nutrients (3–4%).     

Dynamics of planktonic food webs in three mining lakes across a pH gradient (pH 2–4)

Acidic mining lakes (ML) in Lusatia (Germany) are characterised by their geogenically determined chemistry. The present study describes the structure, main components and relationships within the food webs of three acidic mining lakes with different pH values (ML 111: pH 2.6; ML 117: pH 2.8; ML Felix: pH 3.6) in order to show their typical characteristics. The investigation covered the period 1995–1997. The number of species and the biomass are both low, but increase with increasing pH. Planktonic components in the most acidic ML 111 (pH 2.6–2.9) comprise bacteria, Ochromonas spp. and Chlamydomonas spp. and a few rotifers (E. worallii, C. hoodi). Heliozoans are the top-predators. In ML 117 (pH 2.8–3) Gymnodinium sp., ciliates, the rotifer B. sericus and the pioneer crustacean Chydorus sphaericus join the pelagial community. Heliozoans were not found in ML 117 or ML Felix (pH 3.4–3.8). ML Felix had the most taxa. The benthic food chain of all three lakes includes phytobenthic algae as producers, chironomids as primary consumers and corixids as top predators in the profundal. Corixids predate on small cladocerans inhabiting the pelagial in lakes with a pH above 2.8 such as ML Felix. They invade the pelagial and act as a connecting link between the benthic and the pelagic food chains, which are isolated in lakes with a lower pH. Occasionally primary producers and consumers were abundant in all three lakes. These organisms do not depend on the degree of acidity, but on the availability of essential ressources. Mass variations covered up any seasonal variation in the extremely acidic ML 111 (0.9 mm³ l^–1), while in the other two lakes seasonal patterns of biomass were found.     

Seasonal changes in the abundance and distribution of planktonic rotifers in Grasmere (English Lake District)

SUMMARY. The planktonic rotifers of Grasmere, a small lake in the English Lake District, were studied from August 1969 to December 1972. Twenty-four species were recorded but five were very rare. The remaining species were divided into three groups according to their seasonal occurrence: spring to autumn species ( Keratella quadrata. K. cochlearis, Gastropus stylifer, Asplauduia priodonta. Kellicottia Umgispina, Conochilus hippocrepis )., spring to early summer species ( Polyarthra dolichoptera, Synchaeta tremula, S. pectinata, S. stylata, S. oblonga, C. unicornis ), summer to autumn species ( Polyarthra vulgaris, P. major. Filinia terminalis, S. grandis, Ploesoma hudsoni, Trichocerca capucina, T. similis ). The months in which each species was abundant are given.
Keratella quadrata and Filinia terminalis were most abundant in the deepest stratum, Kellicottia longispina and Conochilus spp. were most abundant in the upper and middle strata. Trichocerca spp. showed no pronounced vertical distribution, and all the remaining species were most abundant in the upper stratum. Keratella cochlearis and Kellicottia longispina attained their highest densities over a wide range of temperature and oxygen concentration. Filinia terminalis, Conchihis spp., Asplanchna priodonta. K. quadrata , and Polyarthra spp., attained their highest densities within a narrow range of temperature and oxygen concentration. Optimum ranges are given for each species.
Major changes occurred between 1971 and 1972 when Asplanchna priodonta. Kellicottia longispina, Conochilus unicornis and Filinia terminalis increased in abundance, whilst Keratella quadrata. Gastropus stylifer, C. hippocrepis, Polyarthra spp., Synchaeta spp. and Ploesoma hudsoni decreased in abundance. These changes are discussed in relation to the temperature and oxygen requirements of each species and also to the probable enrichment of the lake after the opening of a new sewage works in June 1971.     

Rotifers as indicators of lake types in Estonia

Data on the pelagic rotifer fauna in 10 Estonian lakes accumulated for 20 years, as well as published data are analysed. It is possible to distinguish three main indicator groups among rotifers: (1) for oligo- and mesotrophic lakes (Ploesoma hudsoni, Keratella serrulata, Synchaeta grandis, Asplanchna herricki, Ascomorpha ovalis, Gastropus stylifer, Conochilus hippocrepsis); (2) for meso-and eutrophic lakes (Trichocerca capucina, Filinia longiseta, F. limnetica, Keratella quadrata, K. cochlearis tecta, K.c. hispida, Polyarthra euryptera, Keratella hiemalis, Trichocerca porcellus, T. pusilla); (3) for eutrophic lakes (Brachionus spp., Anuraeopsis fissa, Pompholyx sulcata, P. complanata, Trichocerca cylindrica, Hexarthra mira).     

Limnological characteristics of subtropical Lakes Phewa, Begnas, and Rupa in Pokhara Valley, Nepal

Limnological characteristics were studied and analyzed in the subtropical Lakes Phewa, Begnas, and Rupa of Pokhara Valley, Nepal, from 1993 to 1997. The annual water temperature ranged from 12° to 29°C in all lakes. Lake Phewa and Lake Begnas were monomictic and anoxic in the hypolimnion during thermal stratification from April to September. Dissolved oxygen was drastically depleted in April and/or May in shallow Lake Rupa when the macrophyte community began to decompose. NH₄ ⁺-N accumulated below 5 m during March–September when dissolved oxygen was depleted in Lakes Phewa and Begnas. The PC : PP ratio was higher, but the PC : PN and PN : PP ratios were close to the Redfield ratio (106C : 16N : 1P) in Lakes Phewa and Begnas, denoting that P was limited. Annual net primary production showed that the lakes were productive but will tend to become heterotrophic in the future. The seasonal variation of chlorophyll a concentration was high, but its annual variation was low. Ceratium hirundinella and Peridinium spp. in Lake Phewa, Microcystis aeruginosa and Aulacoseira granulata in Lake Begnas, and Tabellaria fenestra in Lake Rupa were the dominant species. The zooplankton population and species varied irregularly. On the basis of chlorophyll a concentration in the euphotic zone and phytoplankton species composition, the lakes seem to be oligoeutrophic and to have some characteristics of temperate lakes rather than tropical lakes. Received: April 26, 1999 / Accepted: September 20, 1999     

Acoustic observations of zooplankton in lakes using a Doppler current profiler

1. In this paper we test the usefulness of acoustic backscatter measurements from a 614 kHz Acoustic Doppler Current Profiler (ADCP) for the qualitative and quantitative characterisation of zooplankton distributions in lakes. ADCP‐based backscatter estimates were compared with frequent net hauls obtained during a calibration experiment in which the acoustic backscatter was strongly dominated by vertical migrating Chaoborus flavicans larvae. 2. The correlation between backscatter estimates and the C. flavicans concentration was very good. Vertical swimming speed of larvae, measured directly by the ADCP, was up to a maximum of 5 mm s^?1 and agreed very well with the observed vertical movement of the backscatter contour lines. Although the strong backscatter from C. flavicans overwhelmed the signal from the remaining zooplankton, a good correlation between backscatter strength and the total remaining zooplankton concentration, dominated by Cyclops spp., was found for the depth and time intervals where no C. flavicans were present. 3. In addition to the calibration experiment, longer‐term ADCP measurements from different lakes revealed a strong temporal correlation between the onset of the up‐ and downward migration of zooplankton and the local sunset and sunrise. 4. We conclude that ADCPs can be used to monitor plankton distributions both temporally and spatially. It also seems possible to estimate plankton densities after appropriate calibration.     

The Filtering Rates of Four Herbivorous Crustaceans on Nannoplankton and Net Plankton Fractions in an Acid Lake in West Virginia

Four experiments were conducted in Cheat Lake, West Virginia, to determine the filtering rates of zooplankton on the size fractions of phytoplankton in an acid lake. The results showed that Bosmina longirostris filtered significantly more net plankton than nannoplankton. Results for other species were not consistent in the size fraction selected. The dominance of Peridinium inconspicuum may have made the nannoplankton fraction unavailable as food for Bosmina.     

Zooplankton community composition of lakes in the Yukon and Northwest Territories (Canada): relationship to physical and chemical limnology

We analysed associations between zooplankton species composition and local abiotic factors in 30 lakes located along a 900 km south-north transect from Whitehorse (Yukon Territory) to Inuvik (Northwest Territories). The lakes were situated in three broadly defined vegetation zones: (i) Boreal forest (between Whitehorse and Dawson City), (ii) alpine tundra (Ogilvie mountains north of Dawson City) and (iii) subarctic forest-tundra (near Inuvik). Lakes in the alpine tundra were characterised by lower conductivity, temperature, chlorophyll a and nutrients than those in the other two zones. Those in the forest-tundra were generally small and shallow, and had higher chlorophyll a concentrations than lakes further south. Lakes in forested catchments spanned a larger latitudinal range and exhibited a greater variety of physical and chemical characteristics. However, they were generally deeper, with higher conductivity, temperature and ionic concentrations. Forty-one zooplankton taxa were identified from the 30 lakes, of which the most frequently occurring were the rotifers Conochilus unicornis, Kellicottia longispina, Keratella cochlearis and Polyarthra vulgaris, the cladocerans Daphnia middendorffiana and Bosmina longirostris, and the copepods Leptodiaptomus pribilofensis, Heterocope septentrionalis and Cyclops spp. The lakes contained between two and fifteen species (mean = 6.9). Alpine tundra lakes contained slightly less species (mean = 5.8) than those at lower elevations; in particular the cladoceran fauna was depauperate or absent. Relationships among the lakes, species and environmental factors were examined using canonical correspondence analysis, with forward selection and associated Monte Carlo permutation tests. Chloride, silica and temperature showed statistically significant relationships with species distribution, and together these abiotic factors explained 25% of the variation in zooplankton communities within Yukon and Northwest Territories lakes.     

Nonadditive effects of consumption in an intertidal macroinvertebrate community are independent of food availability but driven by complementarity effects

Suboptimal environmental conditions are ubiquitous in nature and commonly drive the outcome of biological interactions in community processes. Despite the importance of biological interactions for community processes, knowledge on how species interactions are affected by a limiting resource, for example, low food availability, remains limited. Here, we tested whether variation in food supply causes nonadditive consumption patterns, using the macroinvertebrate community of intertidal sandy beaches as a model system. We quantified isotopically labeled diatom consumption by three macroinvertebrate species (Bathyporeia pilosa, Haustorius arenarius, and Scolelepis squamata) kept in mesocosms in either monoculture or a three‐species community at a range of diatom densities. Our results show that B. pilosa was the most successful competitor in terms of consumption at both high and low diatom density, while H. arenarius and especially S. squamata consumed less in a community than in their respective monocultures. Nonadditive effects on consumption in this macroinvertebrate community were present and larger than mere additive effects, and similar across diatom densities. The underlying species interactions, however, did change with diatom density. Complementarity effects related to niche‐partitioning were the main driver of the net diversity effect on consumption, with a slightly increasing contribution of selection effects related to competition with decreasing diatom density. For the first time, we showed that nonadditive effects of consumption are independent of food availability in a macroinvertebrate community. This suggests that, in communities with functionally different, and thus complementary, species, nonadditive effects can arise even when food availability is low. Hence, at a range of environmental conditions, species interactions hold important potential to alter ecosystem functioning.     

Plankton communities of an acidic,polymictic, brown-water lake

The plankton of an acidic, polymictic, brown-water lake was investigated over a one-year period. The phytoplankton community was dominated by Chlamydomonas sp., Melosira varians and Peridinium pusillum during different times of the year. Densities were abnormally low, with a maximum of only 13,781 individuals per liter during the March bloom. The water column was nearly void of phytoplankton during the fall. These low densities were attributed to several of the physical and chemical characteristics of the water, including low pH, low levels of nutrients and light limitation. The latter factor was important because of low light transmission into the highly colored water, shading from macrophytes and the nearly continuous transport of the phytoplankton into the aphotic zone due to mixing of the water column by sea breezes.The zooplankton was dominated by Diaptomus floridanus, Polyarthra vulgaris, Keratella cochlearis and Daphnia ambigua. The observed densities were typical of southeastern oligotrophic lakes. The zooplankton community did not exhibit a decrease in density that corresponded with the observed low phytoplankton densities, suggesting the possibility that they relied heavily on bacterial and detrital food sources.     

Survival and development of five species of cyclopoid copepods in relation to food supply: experiments with algal food in a flow-through system

1. Cyclops spp. generally develop and grow during favourable food conditions in spring and undergo a diapause in summer, while Acanthocyclops robustus, Mesocyclops leuckarti and Thermocyclops crassus develop and grow in summer when they face poorer food conditions and more competition from Cladocera. Since nauplii are the bottleneck in copepod development, we tested the hypothesis that Cyclops abyssorum and C. vicinus nauplii have higher food requirements for survival and development than the nauplii of A. robustus, M. leuckarti and T. crassus. We also tested survivorship and development from hatching to adulthood. 2. Survivorship and development of the copepods was studied in a flow‐through system using five concentrations of the phytoflagellate Chlamydomonas reinhardtii in the range from 1 × 10⁴ to 4.5 × 10⁵ cells mL^?1 (approximately 0.5–22.5 mg C L^?1). 3. Nauplii of both species of Cyclops died at intermediate to low (C. abyssorum) and low (C. vicinus) food concentrations, while nauplii of A. robustus, M. leuckarti and T. crassus survived at all concentrations. 4. The negative effects of low food concentration were also reflected in development. In C. abyssorum and C. vicinus, development duration increased at low food concentration while development was much less affected in A. robustus and T. crassus. Mesocyclops leuckarti was intermediate between Cyclops spp. and A. robustus/T. crassus, with an increase in development duration at the lowest food concentration. 5. Our results support the hypothesis that summer diapause in Cyclops spp. has developed as a strategy to avoid a food bottleneck for nauplii.     

Importance of algae in the diet of the oligochaetes Lumbriculus variegatus (MÜller) and Rhyacodrilus sodalis (Eisen)

Summary The importance of algae in the diet of the oligochaetes Lumbriculus variegatus and Rhyacodrilus sodalis was determined from cellections made in a eutrophic bay from April 1977 to April 1978. During the summer, algae represented 70–85% of the gut contents of both species. The most frequently ingested algae were Cymatopleura elliptica, Cymbella spp., Epithemia turgida, Pinnularia spp., and Synedra ulna. Almost all species were consumed in proportion to their abundance in the environment. However, Nostoc pruniforme and Nostoc verrucosum were not eaten due to size selection. The high level of algal consumption exhibited by the oligochaetes was primarily related to the large standing crop of algae on the sediments. During the winter, when algal densities were low in the environment, detritus and associated bacteria were the major food source.     

The response of the frugivorous lion-tailed macaque (Macaca silenus) to a period of fruit scarcity

Tropical rainforests show seasonal fluctuations in the abundance of fruits resulting in periods of resource scarcity for frugivores. We examined the response of an obligate frugivore, the lion‐tailed macaque (LTM) (Macaca silenus), to a period of fruit scarcity in a rainforest in the Western Ghats, India. We estimated the abundance and distribution of fruit resources from food tree densities obtained from 348 point centered quadrats, and fruit availability from phenological monitoring of 195 trees of 15 reported major food species. Macronutrient content was estimated for fruits of 15 major food species. We estimated time spent feeding on different food items from 1,853 individual scans spanning 120 hr of observation of one habituated study group. There was a distinct period of fruit scarcity during the drier months of February to mid‐March (Period 1) compared with late March and April (Period 2), separated by summer showers. Fruits available in Period 1 had lower soluble carbohydrate and lipid content and overall caloric value compared with Period 2. During the lean period, the LTM fed more on fruits of Drypetes wightii, which had the highest carbohydrate content, than on nectar of Palaquium ellipticum or Ficus spp., which had low carbohydrate content. During this period, the resource availability in a location significantly influenced the occurrence of feeding there. In Period 2, the group fed most on the seeds of Cullenia exarillata, the most abundant tree in the home‐range and with the highest content of soluble carbohydrates. During this period, the abundance of food trees in fruit in a location did not seem to influence the occurrence of feeding. Low abundance, stochastic fruiting and, low quality might make Ficus spp. a poor fallback option for the LTM. Am. J. Primatol. 73:1250–1260, 2011. © 2011 Wiley Periodicals, Inc.     

A regression analysis of the summer population dynamics of Polyarthra vulgaris in a northern Michigan bog lake

The population dynamics of a planktonic rotifer (Polyarthra vulgaris) were examined in a brown water, acid lake in northern Michigan, U.S.A. Predation by Chaoborus punctipennis and low food (Navicula spp. and Cyclotella spp.) concentrations were the main factors limiting P. vulgaris populations of all factors examined. The data presented here support a hypothesis for zooplankton limitation by an invertebrate predator.     

Winter phytoplankton community structure in three shallow temperate lakes during ice cover

The general model of seasonal phytoplankton succession in temperate lakes suggests that winter phytoplankton growth is minimal under ice-cover. However, some studies have found diverse phytoplankton communities during winter. The primary objectives of this study were to determine the species composition and the changes in the winter phytoplankton community structure under the ice. For 2 consecutive winters, phytoplankton samples were collected under ice-cover at 4 sites on 3 lakes in Arrowwood National Wildlife Refuge (ANWR), near Pingree, North Dakota. Ninety taxa were identified and enumerated. Densities of several of these taxa frequently exceeded 10⁶ cells l^–1. The winter phytoplankton communities in these lakes were dominated by flagellates, principally cryptomonads, a synurophyte (Synura uvella), small chrysophytes (Chrysococcus spp., Kephyrion spp.) and a dinoflagellate (Peridinium aciculiferum), as well as non-flagellate microchlorophytes (Monoraphidium spp., Ankistrodesmus spp., and Pseudodictyosphaerium sp.), a cyanobacterium (Gloeocapsa aeruginosa) and centric diatoms (Stephanodiscus minutulus, S. parvus and Cyclotella meneghiniana).     

CHRYSOPHYTE POPULATION AND ENCYSTMENT PATTERNS IN TWO CANADIAN LAKES1

The dynamics of chrysophyte populations and the onset of encystment in relation to several physical, chemical, and biological variables were studied in two Canadian lakes, Lake Opinicon (LO) and Upper Rock Lake (URL). LO is shallow and polymictic during the ice-free season, whereas URL is deep and dimictic. Seasonal patterns of many limnological variables, as well as species composition and seasonal dynamics of chrysophyte assemblages, were broadly similar in both lakes. Three groups of chrysophytes were recognized: 1) taxa that were more abundant during ice cover and/or early spring and occasionally in late fall (Dinobryon spp. Ehrenberg and Synura spinosa Korsh), 2) taxa that seemed to prefer moderately warm water proglena americana Calkins and Ochromonas sp. Wyssotzki) and had maximum densities in late summer and occasionally in the fall, and 3) taxa that occurred in low numbers and did not exhibit any discernible seasonality in the two lakes (Mallomonas spp. Perty). Encystment rarely occurred during ice cover in both lakes. Stomatocyst concentrations were highest shortly after ice breakup (late April or early May), declined to trace levels by June, and remained at those levels until the end of the sampling season (late November). Encystment rates (cyst concentrations) were higher in dimictic URL. Encystment in both lakes coincided with concurrent changes in physical and chemical variables and chrysophyte vegetative cell densities, but it was not possible to pinpoint the exact conditions responsible for triggering encystment. Only a small proportion of chrysophytes encysted. Cyst production within a lake may vary from year to year.     

Some Factors Influencing the Diversity and Species Composition of Benthic Invertebrate Communities in Twenty Arctic and Subarctic Lakes

The factors influencing the density, diversity and species composition of benthic invertebrate communities in 20 lakes in the Canadian arctic and subarctic were determined during 1975, 1976 and 1977. Despite small differences in nutrient and phytoplankton levels among the lakes, there was a strong positive correlation between these parameters and the density and diversity of the communities. Other factors, including maximum summer water temperature, lake depth and surface area had little overall effect on the communities. The densities of 2 ultra-oligotrophic chironomids (Heterotrissocladius oliveri and Micropsectra cf. groenlandica) increased markedly in cold deep lakes. However the abundance of the majority of species, most notably Procladius denticulatus, Tanytarsus sp., and Stictochironomus sp., was not effected by temperature. Other species, (Pontoporeia affinis, Monodiamesa bathyphila and Dicrotendipes nervosus) were probably restricted in their northern distribution by temperature. Surface area usually had little effect on the densities of all common species.