Zooplankton in Lake Atnsjøen 1985–1997

The aim of this paper is to study long-term changes in the zooplankton of a subalpine locality unaffected by direct anthropogenic disturbances. The material has been collected during the period 1985–1997; since 1988 a standardised sampling program has been followed, with five sampling dates during the ice free period (June–October) at three fixed stations. Altogether 17 species of Rotatoria, 9 species of Copepoda and 11 species of Cladocera were recorded. Of these 10 species of Rotatoria, two species of Copepoda and five species of Cladocera occur regularly in the plankton. Polyarthra vulgaris dominate among the rotifers together with Kellicottia longispina and Conochilus unicornis. The crustacean community is dominated by the copepod Cyclops scutifer, and the cladocerans Bosmina longispina, Holopedium gibberum and Daphnia longispina. The cladocerans Bythotrephes longimanus, Polyphemus pediculus,and the copepodsArctodiaptomus laticeps and Heterocope saliens all occur regularly, but at low densities. The zooplankton density is low in May/June and peaks in August and September, but the timing of maximum densities varies from year to year. By numbers, the rotifers strongly dominate with densities 10–15 times higher than the crustaceans. The annual maximum density (rotifers plus crustaceans) ranged from 50 ind. l^?1 (1985, 1988) to 450 ind. l^?1 (1995). Mean density is about 140–150 ind. l^?1. By biomass (dry weight), the cladocerans constitute 60%, while the copepods and rotifers constitute 30% and 10% of the zooplankton, respectively. The annual maximum has varied between 70 and 260 μg dw l^?1, with 170 μg dw l^?1 as the mean level. C. scutifer usually has a one-year lifecycle without diapause, but a small fraction of the population has a two-year lifecycle. The life cycle in 1989 and 1990 differed strongly from the other years. The life cycles of B. longispina, D. longispina and possibly also H. gibberum and A. laticeps, indicate two generations during the summer. H. gibberumandH. saliens pass the winter as resting eggs. The other crustacean species, except C. scutifer, pass the winter mainly as resting eggs, but all have a small winter population in the water mass. C. scutifer is the only species without resting eggs. The vertical distribution normally shows highest density between 5 and 10 m depth. However, during some periods maximum density is observed close to the surface, while at other times it is seen deep in the hypolimnion. The vertical distribution is most pronounced when the thermocline is sharp, and less pronounced during the full circulation in autumn. The vertical migration may also be pronounced, especially in B. longispina, with high density near the surface during the night. The vertical migration is less pronounced among the rotifers and copepods. The degree of vertical migration varies with temperature and food conditions. There is little variation from year to year in species composition, but large variation in species dominance, seasonal development, population density, and vertical and horizontal distribution during the sampling period. Variations in temperature, food condition, predation, and water through-flow are possible causes for the observed differences between the years. Input of allochthonous material is especially important. However, no clear correlation have been found between the development of the plankton community and these environmental factors. Hence, these interactions are complex and multifactorial.     

Zooplankton community changes in Lake Kinneret (Israel) during 1969–1985

Long-term records (1969–1985) of zooplankton density in Lake Kinneret indicated significant reduction of biomass (Copepods, Cladocera, Rotifera) and production (Copepods, Cladocera). Nauplius and adult copepod densities decreased but those of copepodites did not change. Mesocyclops was suppressed more than the smaller Thermocyclops and males of both genera became more abundant relative to the larger females. Ratios of small/large Cladocera densities became higher. Numbers of total cladocerans were stable, and therefore reduction of Cladocera grazing capacity is assumed. The abundant Keratella spp. were reduced. It is likely that intensification of fish visual-attack-predation pressure shifted the size-class structure towards smaller adult copepods and cladocerans. Reduction of Keratella spp. and copepod nauplii was probably affected by increasing pressure of fish filter-feeders. Data on fish food consumption, feeding behaviour and fisheries management suggested their direct impact on long-term changes of zooplankton in Lake Kinneret.     

Spatial–temporal patterns of methane dynamics in Lake Taihu

Many European lakes are monitored according to the EU Water Framework Directive (WFD), with focus on phytoplankton biomass and species composition. However, the low-frequency WFD monitoring may miss short-term phytoplankton changes. This is an important issue because short-term extreme meteorological events (heat waves and heavy rain) are predicted to increase in frequency and intensity with climate change. We used records from Lake Mondsee (Austria) from 2009 to 2015 to test if a reduction from monthly to seasonal sampling affected the average annual phytoplankton biovolume. Furthermore, we combined inverted light microscopy, FlowCAM and flow cytometry to estimate the effect of sampling during extreme events on average phytoplankton biovolume. Relative to monthly sampling, seasonal sampling significantly overestimated phytoplankton biomass. A heat wave in 2015 and two episodes of heavy rain in 2015 and 2016 caused species-specific changes; biovolumes of chlorophytes and the filamentous cyanobacterium Planktothrix rubescens (De Candolle ex Gomont) Anagnostidis & Komárek increased significantly during the heat wave. Using live material with FlowCAM and flow cytometry, we detected small and fragile cells and colonies that were either ignored or underrepresented by analysing fixed samples with light microscopy. We suggest a modified sampling and analysis strategy to capture short-term changes within the phytoplankton community.     

Zooplankton in Svalbard fjords on the Atlantic–Arctic boundary

Zooplankton abundance and community structures were studied in three west Spitsbergen fjords at the beginning of the warm phase, which seem to have entered in 2006. Sampling was conducted in summer 2007 at stations distributed along transects in Hornsund, Isfjorden and Kongsfjorden. Variations in zooplankton standing stocks and community structures (assessing taxonomic diversity and zoogeographical affiliations) were analysed in relation to the environmental variables using multivariate techniques. The hydrographic conditions in Hornsund were influenced by the cold Arctic Water, whereas those in Isfjorden and especially in Kongsfjorden were, to a greater extent, under the influence of the warm Atlantic Water. High abundances of both meroplankton and holoplankton organisms were observed in Kongsfjorden, with high contributions of boreal and ubiquitous species (Calanus finmarchicus and Oithona similis, respectively). In Hornsund at the same time, the zooplankton consisted mainly of boreo-Arctic and Arctic species, the abundances of which were comparable along the West Spitsbergen Shelf. Our results indicate that the difference in hydrography had measurable effects on the zooplankton community in the study area. Furthermore, by comparing regions of contrasting oceanographic conditions, we present evidence as to how the zooplankton structure will change in the Arctic ecosystems if the warming trends continue to operate with the same dynamics. The advection of Atlantic waters to the Arctic seas may lead to changes in zooplankton structure, with increased abundance and contributions of boreal and small ubiquitous species. The ‘warmer Arctic fjords’ scenarios may also induce more rapid development of both holoplankton and meroplankton populations and, consequently, modify the trophic interactions in plankton communities.     

Zooplankton of the Tsimlyansk Reservoir and Volga–Don Shipping Canal

Biology Bulletin - Zooplankton in the Tsimlyansk Reservoir and water bodies of the Volga–Don Shipping Canal were studied in August and September 2018. Fifteen species not previously reported...     

Changes of Copepoda populations in Lake Kiret during 1969–1985

Long period analysis of Copepoda populations in Lake Kinneret indicated significant reductions in total biomass and production as well as densities of nauplii and adult stages, particularly females. The reduction of adult Mesocyclops sp. was statistically significant, but that of Thermocyclops sp. was not. Annual averages of eggs/female values and densities of copepodite stages did not show significant changes. Concentrations of adult Thermocyclops sp. became higher relative to the larger genus Mesocyclops sp. It is suggested that densities of large copepods were affected by intensification of predation pressure by particulate feeding fishes. The densities of nauplii were probably reduced by increased predation pressure of filter feeding fish.     

Female preference in the context of male–male interactions in Maylandia zebra of Lake Malawi

The mbuna cichlids of Lake Malawi are a diverse, monophyletic, and recently derived clade. Sexual selection is thought to have accelerated their rapid diversification, though the mechanism by which this has occurred remains unknown. In this study, we examine the effect that male–male interactions have on female preference. We first used a short interaction experiment as a proxy for male dominance. We then measured female preference for (1) a single, isolated male; (2) a group of three, highly ranked males, relative to a group of lower ranked males; and (3) a group of three, mixed-ranked males against a similar group of mixed-rank males. We found that male dominance was highly correlated with male standard length. Female preference for male standard length and for dominance rank was significant in both isolated and group interactions. However, females only showed preference for groups of interacting males when males were segregated by dominance rank, not when groups were composed of both dominant and subordinate males. The results suggest that male–male contests influence female mating decisions. By investigating the rules that dictate the outcomes of such interactions we can elucidate the role that behavior plays in the diversification of this species-rich lineage.     

Zooplankton decline in the Černé Lake (Šumava Mountains,Bohemia) as reflected in the stratification of cladoceran remains in the sediment

Stratigraphy of cladoceran remains in the upper 18 cm of a sediment core from the Lake Černé was studied. The successive disappearance of Bosmina longispina, Daphnia longispina and Ceriodaphnia quadrangula from the upper layers of the sediment corresponds with our knowledge concerning the disappearance of these species from the open water.     

Zooplankton of some water bodies of the Zoological Garden in Kraków

The aim of this study was to register the zooplanktonic organisms in water bodies in the Zoological Garden in Kraków, especially from a point of view of the occurrence of species of the Paramecium aurelia complex. Only P. caudatum was found in one habitat, in several sampling places. The species seems very resistant and can survive in poor or polluted habitats in which the P. aurelia ssp. are eliminated.     

Migrations of Fish in Lake Glubokoе

Daily and seasonal cyclicity, directivity, and area of the fish migration in the main ecological zones of Lake Glubokoe have been revealed with the help of hydroacoustic complexes. Mass appearance of fish in the epipelagial and profundal of the water body is observed at dusk and at night, and they return to the littoral and sublittoral with the dawn. In the summer, vertical migrations of fish occur mainly in the near-surface layers of the water column, and the fish also occupy the profundal in late autumn.     

Size-mediated control of perch–midge coupling in Lake Erie transient dead zones

Transient ecosystem-level disturbances such as oxygen depletion (hypoxia) in aquatic systems modulate species distributions and interactions. In highly eutrophic systems, hypoxic areas (“dead zones”) have expanded around the world, temporarily preventing many demersal predators from accessing their food resources. Here, we investigate how yellow perch (Perca flavescens), an exploited, cool-water mesopredator, interact with their dominant invertebrate prey in benthic habitat–non-biting midge (chironomid) larvae–as bottom-water hypoxia develops in central Lake Erie (United States–Canada) during summer. We apply linear mixed-effects models to individual-level data from basin-wide field surveys on size-based interactions between perch and midge larvae under varying habitat conditions and resource attributes. We test if 1) midge populations (larval body size and density) differ among habitat states (unstratified normoxia, stratified normoxia, and stratified hypoxia); and 2) size-based perch–midge interactions (predator–prey mass ratio or PPMR) differ among habitat states with varying temperature and midge density. Midge populations remained highly abundant after bottom-water oxygen depletion. Despite their high densities, midge larvae also maintained their body size in hypoxic water. In contrast, perch on average consumed relatively smaller (by up to ~64%) midges (higher PPMR) in warmer and hypoxic water, while prey size ingested by perch shrunk less in areas with higher midge density. Our analysis shows that hypoxia-tolerant midges largely allow perch to maintain their consumer–resource relationships in contracted habitats through modified size-mediated interactions in dead zones during summer, revealing plasticity of their trophic coupling in the chronically perturbed ecosystem.     

Seasonal variation of phototrophic picoplankton in Lake Biwa (1994–1998)

Seasonal abundances of phototrophic picoplankton (PP) and heterotrophic nanoflagellates in Lake Biwa were studied from 1994 to 1998. Seasonal variation in cell volume and biomass of the phototrophic picoplankton were also studied. PP were counted using disposable glass microscopic plates, which gave superior accuracy to sample filtration onto membrane filters. Phycoerythrin-rich rod-shaped cyanobacteria (PEC), one of the major components of the picoplankton community, were sparse (about 10⁴ cells ml ^–1) in winter and began to increase in April. Several PEC peaks were observed during the period of thermal stratification, and a rapid fall took place after October or November. In the northern basin, PEC peaked during late June and early July in 3 of the 5 years, and in late summer in the remaining years. Phycocyanin-rich rod-shaped cyanobacteria (PCC) were abundant in the southern basin and were present in smaller numbers in the eutrophic nearshore area of the northern basin; they peaked several times during the period from July to October. Seasonal variations of these two kinds of picoplankton were correlated with seasonal changes in water temperature. Phycoerythrin-rich cylinder-shaped cyanobacteria exhibited narrow peaks in July, their abundance declining as the year progressed. The density of heterotrophic nanoflagellates was greatest in early spring. Average cell volume of PEC was largest in winter, then decreased gradually to a minimum in late summer; after the fall, it recovered to the winter cell volume. This change can likely be attributed to the depletion of nitrogen in the warmer seasons.     

Publications of Anthony Calhoun Clement (1909–1984)

Summary

Two zoeae and the megalopa of the majid crab Macropodia parva were obtained from laboratory material. At 25±1°C and 35% salinity, the first crab appeared 12 days after hatching; survival to the first crab instar was 27%. The larval stages are described in detail and compared with those of the previously described species of the genus Macropodia. Zoeal characteristics of M. parva that differentiate it from other known Macropodia larvae are the naked telson furcae and the absence, in zoea II, of the exopodal setae on the basis of the maxillule.     

Participation of algal–bacterial community in the formation of modern stromatolites in Cock Soda Lake,Altai Region

Modern dolomite stromatolites are found in Cock Soda Lake (Kulunda Steppe) at a salinity of 100–200 g/L and pH of 10. The mineralogical analysis has revealed the presence in the stromatolites of Ca?Mg-carbonates of various compositions. The organisms–edificators of the phototrophic community developing in the lake are determined. They are identified as a part of the mineralized biota (cyanobacteria, bacteria, and eukaryotic alga Ctenocladus circinnatus). Morphological and ultrastructural features of exopolysaccharides secreted by cyanobacteria and bacteria dominant in the phototrophic community are characterized. It is shown that polysaccharides secreted primarily by cyanobacteria have the utmost importance for the formation of stromatolites in Petukhovskoe Soda Lake.     

R. Vanbreuseghem 1909–1993

Editor's Note. Dr Vanbreuseghem was a member of the Mycopathologia Educational Board from 1959 to 1960.     

Abundance and feeding of wintering and migrating aquatic birds in two sampling areas of Lake Balaton in 1983–1985

The investigation was carried out at two sampling areas in Lake Balaton (surface area 600 km²), of which one was hypertrophic and the other was mesotrophic. Species diversity was higher in the hypertrophic area, primarily due to a higher number of Anatid species. Contents of crops, gizzards, and intestines were analysed in 321 of the 361 birds collected. Diet was similar in certain species (Aythya fuligula, A. f. ferina, Anas querquedula) despite differences in the trophic state of their habitats. However, in other species (Anas p. platyrhyncha, Aythya nyroca, Bucephala c. clangula), percentage distribution of food items more or less reflected the food resources of the two areas in the digestive tracts. I concluded that the former species are highly selective in their feeding.     

Dynamics of Redox Changes of Iron Caused by Light–dark Variations in Littoral Sediment of a Freshwater Lake

Depth profiles of oxygen concentration and the redox status of acid-extractable iron were measured in littoral sediment cores of Lake Constance incubated under a light–dark regimen of 12 h. While oxygen penetrated to 3.4±0.2 mm depth in the dark, photosynthetic oxygen production shifted the oxic–anoxic interface down to 4.0±0.2 mm or 5.9±1.6 mm depth, at low or high light intensity, respectively, and caused a net oxygen efflux into the water column. After a light–dark or dark–light transition, the oxygen concentration at the sediment surface reached a new steady state within about 20 min. The redox state of the bioavailable iron was determined in 1-mm slices of sediment subcores. After a dark period of 12 h, 85% of the acid-extractable iron (10.5 μmol cm⁻³ total) in the uppermost 8 mm was in the reduced state. Within 12 h at low or high light intensity, the proportion of ferrous iron decreased to 82 or 75%, respectively, corresponding to net rates of iron oxidation in the range of 244 and 732 nmol cm⁻³ h⁻¹, respectively. About 55 or 82% of the iron oxidation at low or high light intensity occurred in the respective oxic zone of the sediment; the remaining part was oxidized in the anoxic zone, probably coupled to nitrate reduction. The areal rates of iron oxidation in the respective oxic layer (21 or 123 nmol cm⁻² h⁻¹ at low or high light intensity, respectively) would account for 4 and 23% of the total electron flow to oxygen, respectively. Light changes caused a rapid migration of the oxic–anoxic interface in the sediment, followed by a slow redox reaction of biologically available iron, thus providing temporal niches for aerobic iron oxidizers and anaerobic iron reducers.