Seasonal change in a saline temporary lake (Fuente de Piedra,southern Spain)

Fuente de Piedra saline lake is located in an endorheic basin in the south of Spain. This lake is very shallow (0.5 m max. depth during 1987–88) and relatively large (± 1350 ha). It is a temporary playa lake, showing irregular cycles, with frequent seasonal drought and a high degree of unpredictability. The lake was sampled monthly during a relatively rainy year (1987–88, 10.5 months permanence). The result of combined analyses for environmental variables (salinity, temperature and soluble inorganic forms of nitrogen and phosphorus), variables related to biological activity (chlorophyll a, sediment organic matter and redox potential) and the direct analysis of the planktonic community, shows the existence of two periods of dominance by autotrophs. The first occurs during winter, exhibits a progressively higher surface to volume ratio for phytoplankton and is followed in the spring by high zooplankton densities (Moina salina, Fabrea salina) and very low phytoplankton densities, suggesting the existence of a period with a detritus-based food web. The summer period coincides with a community better adapted to high salinities that is dominated by Dunaliella salina, D. viridis, diatoms and the ciliate Fabrea salina, and associated with high ammonium concentrations. A new period of organic matter accumulation could be facilitated, in the last moments before the lake dries, by a progressive decrease in zooplankton abundance.     

Oligochaeta of Lake Taimyr: a preliminary survey

Lake Taimyr in Siberia is northernmost among the world's large lakes: 73°40–75°20N, 99–106°E. The lake area is up to 4650 km² in summer, with a maximum depth of 26 m and a mean depth of only 2.8 m. The ice-free period lasts about three months. The water level sinks 5.5–6 m during winter, so that 85% of the bottom surface is frozen into ice for some time and subjected to negative temperatures, probably down to –20 °C. In artificially melted sediment samples, 75–92% of animals survived. The average summer biomass of zoobenthos is about 1 g m^–2 wet weight, a half of this being formed by Oligochaeta. Altogether 76 samples with 3742 oligochaete specimens collected by V. N. Grëze in 1943–1944 were studied. At least 14 taxa of Tubificidae, Lumbriculidae, and Enchytraeidae were found in the lake, and some more enchytraeids in an adjacent river. Many immature animals could not be identified to species. Naididae were completely lacking probably due to the absence of macrovegetation. The shallow freezing zone is inhabited mostly by Alexandrovia ringulata. The profundal fauna is dominated by Lamprodrilus isoporus, Stylodrilus sp., and Isochaetides sp.     

Sulfate reduction processes in sediments at different sites in Lake Kinneret,Israel

Lake Kinneret, Israel, is a warm (13–30°C) monomictic lake that stratifies in April and turns over in December. Between January and June each year, a heavy bloom (up to 250 g wet weight n^–2 2) of the dinoflagellate Peridinium gatunense dominates the phytoplankton biomass. In early summer, the bloom collapses, and the sinking Peridinium biomass serves as a trigger for intense sulfate-reduction activity throughout the hypolimnion and within the sediments. The availability of organic matter and sulfate was high shortly after the bloom crash and the beginning of stratification and was lowest in December before overturn. Sulfate-reduction rates at three different sites in the lake were studied. In the sediments, the rates varied seasonally and among stations from 5 to 1600 nmol SO₄ ^–2 reduced cm^–3 day^–1, with respect to the distance from the Jordan River, depth, organic content, and stratification period. During years of low lake water levels, intense sulfate reduction occurred in the hypolimnion, resulting in anoxia and high concentrations of H₂S (>400 m). In years with high water levels, early bloom, and delayed stratification, higher rates of sulfate reduction were recorded in the sediments, probably as a result of a greater fraction of the primary production (organic matter) reaching the bottom. Correspondence to: O. Hadas.     

A bloom of Dunaliella parva in the Dead Sea in 1992: biological and biogeochemical aspects

A bloom of the unicellular green alga Dunaliella parva (up to 15 000 cells m1^–1) developed in the upper 5 m of the water column of the Dead Sea in May-June 1992. This was the first mass development of Dunaliella observed in the lake since 1980, when another bloom was reported (up to 8800 cells m1^–1). For a bloom of Dunaliella to develop in the Dead Sea, two conditions must be fulfilled: the salinity of the upper water layers must become sufficiently low as a result of dilution with rain floods, and phosphate must be available. During the period 1983–1991 the lake was holomictic, hardly any dilution with rainwater occurred, and no Dunaliella cells were observed. Heavy rain floods in the winter of 1991–1992 caused a new stratification, in which the upper 5 m of the water column became diluted to about 70% of their former salinity. Measurements of the isotopic composition of inorganic carbon in the upper water layer during the bloom (¹³C = 5.1) indicate a strong fractionation when compared with the estimated –3.4 prior to the bloom. The particulate organic carbon formed was highly enriched in light carbon isotopes ( ¹³ C = – 13.5). The algal bloom rapidly declined during the months June–July, probably as a result of the formation of resting stages, which sank to the bloom. A smaller secondary bloom (up to 1850 cells m1–1) developed between 6 and 10 m depth at the end of the summer. Salinity values at this deep chlorophyll maximum were much beyond those conductive for the growth of Dunaliella, and the factors responsible for the development of this bloom are still unclear.     

Limnological survey of the warm monomictic lake Trichonis (central western Greece); I. The physical and chemical environment

The physical and chemical status of Trichonis – the largestanddeepest natural lake in Greece – is examined over two annualcycles (1985–86 and 1988–89). A correlation between lakenutrientpatterns and phytoplankton biomass is attempted. Limnologicalfeatures are compared with data from other warm and temperatelakes.With regard to its thermal regime, Trichonis is classified asawarm monomictic lake. The lake's stratification pattern andannualheat budget resemble those of other temperate lakes. Trichonisisa carbonate type, low conductivity lake (class II, lowsalinitywarm lake). Nitrogen and phosphorus concentrations were ratherlow.The inorganic nitrogen content fluctuated widely over the twoannual cycles examined. On the contrary, phosphorusconcentrationsshowed no significant changes. The limiting factor during1985–86was P, while N was limiting during stratification in 1988–89.Aweak correlation was found between the plankton communityfeatures(species abundance, biomass, chlorophyll-a) and lightpenetration. At present the eutrophication process fromoligotrophytowards mesotrophy has not been essentiallyaccelerated.     

Perennially ice-covered Lake Hoare,Antarctica: physical environment,biology and sedimentation

Lake Hoare (77° 38 S, 162° 53 E) is a perennially ice-covered lake at the eastern end of Taylor Valley in southern Victoria Land, Antarctica. The environment of this lake is controlled by the relatively thick ice cover (3–5 m) which eliminates wind generated currents, restricts gas exchange and sediment deposition, and reduces light penetration. The ice cover is in turn largely controlled by the extreme seasonality of Antarctica and local climate. Lake Hoare and other dry valley lakes may be sensitive indicators of short term (< 100 yr) climatic and/or anthropogenic changes in the dry valleys since the onset of intensive exploration over 30 years ago. The time constants for turnover of the water column and lake ice are 50 and 10 years, respectively. The turnover time for atmospheric gases in the lake is 30–60 years. Therefore, the lake environment responds to changes on a 10–100 year timescale. Because the ice cover has a controlling influence on the lake (e.g. light penetration, gas content of water, and sediment deposition), it is probable that small changes in ice ablation, sediment loading on the ice cover, or glacial meltwater (or groundwater) inflow will affect ice cover dynamics and will have a major impact on the lake environment and biota.     

Limnological survey of Lake Amvrakia, western Greece

Limnological characteristics of lake Amvrakia, a deep warm monomictic and sulphate lake in western Greece, are presented. A set of physical and chemical variables were monitored for one year cycle (October 1988–September 1989). Phytoplankton community structure and biomass are given for the entire depth of the water column. The trophic status of the lake is compared to that of other temperate and tropical lakes.     

Some ecological aspects of Lake Qarun,Fayoum, Egypt. Part I. Physico-chemical environment

The lake situation and morphometry, climatic conditions, water balance and level, hydrology and hydrochemistry of lake Qarun were investigated.Salinity proved to be the most important factor affecting the lake water. Annual changes in salinity of the lake water were recorded. In 1906, the salinity ranged from 10.65 and 11.26, while in 1974–1976 it reached 30.9–34.5.The physico-chemical properties of the lake change greatly owing to climatic and anthropological factors.     

Dynamics of lake herring (Coregonus artedi) reactive volume for different crustacean zooplankton

Lake Torrens, a large ( 6000 km²), episodic, saline playa lake in arid central Australia, filled for the first recorded time in March 1989. This unique event followed unprecedently heavy rain over its catchment. Water remained in the lake until early 1990. Salinities remained low (<40 g l^-1) until November 1989, then increased rapidly to >200 g l^-1 before the water evaporated completely. Na and Cl probably dominated the ions. Twenty-nine taxa of aquatic animals were recorded. Crustaceans dominated and of these Parartemia minuta (anostracan), Daphniopsis queenslandensis and Moina baylyi (cladocerans), and several species of ostracods were the most important. Other significant taxa included Tanytarsus barbitarsis (chironomid), Brachionus plicatilis (rotifer) and Craterocephalus eyresii (fish). The fauna was dominated by widespread forms that are either part of a distinct assemblage found widely in central Australian salt lakes (especially P. minuta, D. queenslandensis, M. baylyi and Trigonocypris subglobusus [ostracod]), or cosmopolitan forms (B. plicatilis), or forms found widely in Australian salt lakes (e.g. Diacypris compacta, Tanytarsus barbitarsis). However, possibly three new species also occurred: a new species of a new genus of mytilocypridinid, Branchinella nov.sp. and Heterocypris nov. sp. Their occurrence is anomolous. It is suggested that further work will show that they too are widely distributed. Both genera of the latter two taxa are typical of temporary waters and specimens may have been washed in from nearby water-bodies. Sixty-four species of bird were recorded when the lake contained water, many breeding. The breeding of the banded stilt (Cladorhynchus leucocephalus) was notable; breeding of this species had been unknown in South Australia since 1930. A large population built up until breeding was stopped by predation from the silver gull (Larus novaehollandiae). When dry, the lake has a depauperate but well-defined and regionally restricted terrestrial fauna (scorpions, spiders, beetles, ants).     

Colonization and succession of submerged macrophytes in shallow Lake Væng during the first five years following fish manipulation

Colonization of submerged macrophytes and changes in species composition were studied in shallow Lake Væng during the first five years (1987–91) following fish manipulation in 1986–1988 and a resultant significant improvement in lake water transparency. No submerged macrophytes were present in the lake from 1981–1986, during which time the summer mean Secchi depth ranged from 0.6 and 0.8 m. From 1987 to 1990, Secchi depth increased from 0.9 m to 1.8 m and macrophyte coverage consequently increased (1 % of the lake area in 1987, 2% in 1988, 50% in 1989, 80% in 1990 and 90% in 1991). At the same time, the macrophytes became taller, and the weedbeds more dense. The macrophytes colonized from the exposed and deeper part of the lake towards the sheltered and more shallow part of the lake, a colonization pattern that was confirmed by transplantation experiments. The delay in colonization of the shallow parts may be caused by waterfowl grazing. The vegetation was initially dominated by Potamogeton crispus L., but there was a gradual change during 1988–1989 and Elodea canadensis Michx became exclusively dominant in 1990–1991.     

Distribution and abundance of littoral benthic fauna in Canadian prairie saline lakes

The littoral benthos of 18 lakes in Alberta and Saskatchewan ranging in salinity from 3 to 126 (g1^–1 TDS) were investigated twice, in the spring and in the summer of 1986. Multiple Ekman dredge samples were taken at water depths of about 0.5, 1.0 and 2 metres in each transect. Two to three transects were used in each lake according to its estimated limnological diversity for a total of 114 stations. A total of 76 species was present varying from 29–31 species in the three lakes of lowest salinity (means of 3.1–5.55) to only 2 species in lakes exceeding 100. Species richness decreased rapidly in salinities greater than 15.Biomass maximum mean of 10.91 g m^–2 dry weight (maximum 63.0 g m^–2) occurred in culturally eutrophic Humboldt Lake (3.1) but one third as great in other low salinity lakes. However, biomass again increased to about 4.5 gm^–2 in two lakes of 15 As the salinity increased still further biomass declined steadily until a minimum of 0.0212 g m^–2 was recorded in most saline Aroma Lake (mean 119). Summer biomass (11 lakes) was greater than spring biomass (4 lakes) because some groups such as amphipods, corixids and ostracods became more abundant in summer. Wet weight biomass averaged 15.8 of dry weight biomass.Seasonality (spring or summer), sediment texture and organic matter content, water depth, pH, salinity (TDS) and the presence of aquatic plants ( plant cover) were considered in the matrix involving species dry weight biomass at each of 117 stations. TWINSPAN classification of the samples yielded a dendrogram with 18 indicator species. Successive dichotomies divided these indicator species into four main lake groups based on salinity, i.e., Group I: 3–10 (Gammarus, Glyptotendipes I, Chironomus cf. plumosus), Group II: 10–38%. (Hyalella, Enallagma,Bezzia), Group III: 38–63 (Hygrotus salinarius, Cricotopus ornatus), Group IV: >63 (Dolichopodidae, Ephydra hians). Each of these main groups was subdivided into smaller groups of lakes based on factors such as pH, seasonality (spring or summer species dominance), organic matter and plant cover. Depth of samples played no apparent role.     

Seasonal and environmental influences on antioxidative protection inPeridinium gatunense in Lake Kinneret

As the only freshwater lake in Israel, Lake Kinneret serves a number of important functions which directly rely upon the viability of the water. The annual outbreak of a dinoflagellate bloom strictly governs the nature of the macro and micro food web and ultimately determines water quality.The freshwater dinoflagellatePeridinium gatunense is subject to a wide range of environmental stresses throughout the spring bloom period. It was confirmed that SOD played an important antioxidative maintainance role throughout the bloom, especially during periods of relatively high photosynthetic activity (820 mg C m^–2 day^–1), when activity reached 500 Units SOD mg protein^–1. In addition, high light stress (>300 mol photons m^–2 s^–1) induced SOD activity, despite the low dissolved inorganic carbon (DIC) concentrations at the end of the bloom (1.3 mM). Catalase activity was only significant at the end of the bloom, peaking at 120 mol O₂ mg protein^–1 min^–1, when induced by photorespiratory activity.A series of experiments withPeridinium cultures showed that 2 × 10^–4 M ascorbate inhibited catalase activity >50% within 15 min incubation, bothin vivo andin vitro. It is suggested that the high concentrations of ascorbate, found previously inPeridinium during early and mid-bloom (0.2–1.6 mM), not only eliminate H₂O₂ build-up, but also prevent (directly or indirectly) the induction of catalase.     

The importance of nitrogen in Pyramid Lake (Nevada,USA), a saline,desert lake

The increase in human development in the downstream portion of the Pyramid Lake drainage basin has resulted in increased nutrient loading to the lake. Since this is a deep, terminal lake, concern over nutrient build up and change in trophic status exists. On the basis of lake chemistry which shows consistently high concentrations of total reactive-P (mean = 55 µg P l^–1) relative to dissolved inorganic-N (DIN) (mean = 15 µg N 1^–1), it has been hypothesized that Pyramid is N-limited. However, no systematic study of nutrient limitation had been undertaken. Nutrient enrichment bioassays conducted throughout an entire year clearly showed that additions of DIN resulted in a 350–600% stimulation of chlorophyll production. Phosphate, when added singly or in combination with DIN, had no effect. This positive response to N-addition was significant at all times of the year except, (1) immediately after complete lake mixing in February when a large pool of hypolimnetic nitrate was injected into the euphotic zone, and (2) during a fall bloom of the nitrogen fixing species Nodularia spumigena. The positive response to N-addition in the bioassay experiments was strong between March and November. However, the seston exhibited only a gradual depletion of nitrogen relative to carbon over this same period. PN:PC ratios suggested no N-deficiency in phytoplankton biomass in February, March and April, moderate N-deficiency in May, June and July and, severe N-deficiency from August until winter turnover. The appearance of nitrogen fixing blue-green algae in September supports the hypothesis of N-limitation in the summer-autumn. In evaluating the nutrient status of a lake, the concepts of nutrient stimulation versus nutrient deficiency versus nutrient limitation must clearly be defined.This paper is dedicated to G. Evelyn Hutchinson who first visited Pyramid Lake in 1933.     

Large-scale patterns of Nodularia spumigena blooms in Pyramid Lake,Nevada, determined from Landsat imagery: 1972–1986

Magnitude and long-term periodicity of summer-autumn blooms of the nitrogen-fixing cyanobacterium, Nodularia spumigena, were characterized for hyposaline Pyramid Lake, Nevada, from Landsat MSS band 3 film negatives. Predicted lakewide mean chlorophyll a concentrations for Landsat overpasses during the July–October Nodularia bloom season ranged from 27 to 72 mg m^–3 with an overall average concentration of 32 ± 7 mg m^–3 between 1972 and 1986. Nodularia blooms were usually annual events. Blooms were not observed on Landsat images in only three of 15 years (1973, 1980, 1982) and midsummer calcium carbonate whitings occurred in two of these years (1973, 1980). Magnitude of Nodularia blooms was highly variable among years and very large blooms, where maximum mean chlorophyll a concentration exceeded one standard deviation of the 15 year overall mean (> 39 mg m^–3) appeared in 1974, 1975, 1977, 1979, 1984, 1985 and 1986. Very large early-July blooms always occurred during or following years of above average fluvial discharge to Pyramid Lake (1984–1986) and were associated with meromixis produced by the large influx of freshwater.Several problems arise using Landsat remote sensing to estimate magnitude and periodicity of scum-forming blue-green algal blooms. These complications may reduce accuracy and precision of phytoplankton biomass estimates made from Landsat images. Nevertheless, Landsat remote sensing enabled us to quantify relative bloom magnitude with limited collection of ground-based data and at a large-scale temporal and spatial resolution not possible using alternative methodologies.     

Comparative limnology of Sambhar and Didwana lakes (Rajasthan,NW India)

Two alkaline saline inland lakes of Indian arid region were studied during 1984 and 1985, to assess functioning and interaction of various environmental and biological factors. Changes in physical and chemical variables, planktonic composition, chlorophyll content and phytoplankton primary productivity were examined.Salinity in both lakes fluctuated from almost fresh water (1.80), to hypersaline (300) and acted as the main controlling factor for almost all the biotic parameters. Maximum total alkalinities were 2162 mg l^–1 and 2090 mg l^–1, respectively in Sambhar and Didwana lakes. Dissolved oxygen ranged from completely anoxic conditions to maxima of 11.68 and 7.29 mg 1^–1, respectively in Sambhar and Didwana lakes. Nutrient enrichment in the lakes was low.The phytoplankton species composition of Sambhar lake was reduced from an earlier reported 20 genera to only 11 (Nostoc, Microcystis, Spirulina, Aphanocapsa, Oscillatoria, Merismopedia, Nitzschia, Navicula, Synedra, Cosmarium and Closterium). Phytoplankton of Didwana was composed of only 9 genera including Anabaena and Nodularia. Sambhar lake, which once contained Artemia, is now totally devoid of them. On the other hand, Artemia was the most dominant zooplankter in Didwana lake at a salinity range of 15–288. Other zooplankters such as Moina, Cyclops and Brachionus flourished at lower salinity levels in Didwana lake. The seasonal quantitative and qualitative phyto- and zooplankton changes in relation to salinity are documented.     

Composition,density and feeding of crustacean zooplankton community in a shallow,temperate lake (Lake Balaton,Hungary)

Composition density and filtering rates of crustacean zooplankton were studied in the open water and among the macrophytes of the oligo-mesotrophic part of Lake Balaton from 1981 to 1983. From the individual filtering rates of the different populations and the densities community grazing rates were derived.Copepoda made up 79–90% of crustacean plankton community in the open lake and 95–97% of it in littoral zone. Among them the nauplii dominated. At the end of summer 1982, when Anabaenopsis was in bloom, the filter-feeding species (Eudiaptomus, Daphnia) practically disappeared, being replaced by cyclopoids. Daphnia had the highest filtering rates followed by those of Eudiaptomus and Diaphanosoma. Among copepods, the filtering rates in decreasing order were: ovigerous > all adults > copepodites > nauplii. > . The filtering rates of the different species varied both seasonally as well as from year to year. In 1983, when the concentration of organic seston decreased, filtering rate increased compared with those in the earlier years. During the water bloom in 1982, the rates decreased by 70% on the average.The community grazing rate was very low (3% per day) in the open lake and among macrophytes, both in 1981 and 1982; also the share of crustacean zooplankton in grazing was very low. In 1983, together with the improving of water quality, the community grazing rate increased 4-fold. In 1981 and 1983 the rates were influenced by water temperature but in 1982 by seston concentration.     

Pigment estimations and photosynthesis of Ruppia drepanensis Tin. ex Guss. in a hypersaline environment

We collected the ephemeral macrophyte Ruppia drepanensis Tin. ex Guss. from the athalassic shallow lake Fuente de Piedra (Málaga. Southern Spain). This lake, situated in an endorheic basin, shows great seasonal changes in depth and Total Dissolved Solids (TDS).Dissolved oxygen evolution studied in the laboratory at 17 different photon flux densities (PFD) showed a maximum rate of photosynthesis of 0.55 mg C g dry wt^–1 h^–1, a light compensation point at 86 µE m^–2 s^–1 and a saturation point at 333 µE m^–2 s^–1. A moderate photoinhibition (\ = 1.68 10^–4) was found above 695 µE m^–2 s^–1.Estimates of pigment concentrations revealed 10 times more carotenoids than chlorophyll.The adaptation of the plants to high irradiances and to the particular features of their hypersaline environment are discussed.     

The annual flood regime as a regulatory mechanism for phytoplankton production in Kainji lake,Nigeria

Phytoplankton production was measured in situ in Kainji lake from December 1970 to September 1972 using the oxygen light and dark bottle technique. Seasonal variations in solar radiation, transparency, temperature, and composition of subsurface light were also measured. Oxygen production per unit area varied from 220 to 4500 mg O₂ m^–2 day^–1, the maximum production rate from 95 to 400 mg O₂ m^–3 h^–1. Seasonal mixing of lake water and river water of varying turbidity changed the optical properties of the lake water and consequently affected phytoplankton production. The annual flood pattern was found to be an important factor regulating phytoplankton production in the lake.     

Phytoplankton dynamics in a deep, tropical, hyposaline lake

The annual variation of the phytoplankton assemblage of deep (64.6 m), hyposaline (8.5 g l^–1) Lake Alchichica, central Mexico (19 ° N, 97° W), was analyzed in relation to thermal regime, and nutrients concentrations. Lake Alchichica is warm monomictic with a 3-month circulation period during the dry, cold season. During the stratified period in the warm, wet season, the hypolimnion became anoxic. N–NH₃ ranged between non detectable (n.d.) and 0.98 mg l^–1, N–NO₂ between n.d. and 0.007 mg l^–1, N–NO₃ from 0.1 to 1.0 mg l^–1 and P–PO₄ from n.d. to 0.54 mg l^–1. Highest nutrient concentrations were found in the circulation period. Chlorophyll a varied from <1 to 19.8 g l^–1 but most values were <5 g l^–1. The euphotic zone (>1% PAR) usually comprised the top 15–20 m. Nineteen algae species were identified, most of them are typical inhabitants of salt lakes. Diatoms showed the highest species number (10) but the small chlorophyte Monoraphidium minutum, the single-cell cyanobacteria, Synechocystis aquatilis, and the colonial chlorophyte, Oocystis parva, were the numerical dominant species over the annual cycle. Chlorophytes, small cyanobacteria and diatoms dominated in the circulation period producing a bloom comparable to the spring bloom in temperate lakes. At the end of the circulation and at the beginning of stratification periods, the presence of a bloom of the nitrogen-fixing cyanobacteria, N. spumigena, indicated nitrogen-deficit conditions. The well-stratified season was characterized by low epilimnetic nutrients levels and the dominance of small single-cell cyanobacteria and colonial chlorophytes. Phytoplankton dynamics in tropical Lake Alchichica is similar to the pattern observed in some deep, hyposaline, North American temperate lakes.     

Macrozoobenthos of Lake Peipsi-Pihkva: taxonomical composition, abundance, biomass, and their relations to some ecological parameters

The large but shallow (3,558 km², up to 15.3 m deep) lake is eutrophic, with Chironomus plumosus and Potamothrix hammoniensis as dominating macroinvertebrates in the profundal. The extensive well-aerated sublittoral with sandy bottom sediments has a mesotrophic appearance and supports a diverse fauna with several oxyphilous species, including a very abundant population of Dreissena polymorpha. The phytophilous fauna is limited to small sheltered areas only. The average abundance of the small animals of macrozoobenthos (without big molluscs) was 2,617 ind. m^–2, their biomass 12.34 g m^–2 (corresponding to 52.2 kJ m^–2) in 1964–1994. The same figures for big molluscs (mostly Dreissena) were 304 ind. m^–2 and 238 g m^–2 in 1964–1994, and even 864 ind. m^–2 and 687 g m^–2 in 1985–1988, at the time of their special mapping. The sublittoral zone revealed the lowest biomass of small animals but the highest biomass of big molluscs. The southern, shallower lake regions, more enriched with nutrients and better protected from wind, revealed a significantly higher biomass of small macrozoobenthos in the near-shore zone than the cleaner and open northern part, while no positive effect of enrichment was observed neither in the biomass of profundal zoobenthos nor in that of big molluscs. The production of the small macrozoobenthos was calculated as 111 and 53 kJ m^–2 during two annual cycles in Lake Peipsi s. s., the most productive period being the autumn overturn. Lake Peipsi-Pihkva has the highest abundance and biomass of macrozoobenthos among the large lakes of North Europe.