Impact of prehistoric settlements on the Cladocera in the sediments of Lakes Suszek,Bł\cedowo,and Skrzetuszewskie

An analysis of Cladocera has been made on sediments from the three Polish lakes Suszek, B\cedowo, and Skrzetuszewskie. The analysed sediments are gyttja from the Subboreal and Subatlantic periods, during which the lakes were subject variously to eutrophication. The eutrophication process has been analysed from the frequency of Cladocera, particularly the index species, and has been correlated with climatic and settlement changes. It was found that in Suszek lake, in which no significant human activity had taken place (palynologically documented), the eutrophication must have been slow and gradual. On the contrary, in the two remaining lakes, in which the human influence was more intense, the eutrophication process underwent intensive changes and coincided somewhat with settlement fluctuations.     

Palaeolimnological study of an environmental monitoring area,or, are there pristine lakes in Finland?

A palaeolimnological study of Lake Iso-Hietajärvi in Patvinsuo National Park, Lieksa, East Finland was conducted. The drainage area of the lake is one of four Integrated Monitoring areas established in Finland. Lead-210 dating reveals a period of increased sedimentation in the lake from 1920 to 1950. Increased atmospheric burden of several heavy metals in the order Pb > Cu> Zn > Ti = Al > Cr = Ni = V is recorded. The first to expand during the 19th century is Pb, whilst V increases after 1950. Sedimentary chlorophyll derivatives expand in the early part of the 20th century. Assemblages of diatoms and Cladocera were also changed somewhat during this time, but water quality seems not to have varied much: e.g. the diatom-inferred pH has remained in the range 6.4–6.8 (with a slight decrease) throughout the period of study.     

Electron transport system (ETS) activity and respiration rate in five Daphnia species at different temperatures

Electron transport system activity (ETS) andrespiratory rate (R) were measured in five Daphnia species at different temperatures in thelaboratory. The animals were collected from differenthabitats: Daphnia hyalina Leydig from aneutrophic subalpine lake, D. pulicariaForbes from an oligotrophic high-mountainlake, D. pulex Leydig from a temporary lowlandpool, and D. obtusa Kurz from a temporaryhighland pool. D. magna Straus was obtained fromlaboratory cultures.ETS activities and respiratory rates were studied injuveniles and adult females without eggs. The rateswere measured at 5, 10, 15, and 20 °C. Foradult females Q₁₀ of ETS-activity ranged from 1.9for D. pulicaria to 2.2 for D. obtusa. Thevalues for juvenile individuals showed greatervariations, ranging from 1.6 for D. pulicaria to3.4 for D. hyalina. Q₁₀ values forrespiration were from 1.3 to 1.7 for adults, and from1.4 to 2.1 for juveniles. The accelerating effect oftemperature (µ) ranged from 18.5 to 93.4 kJ mol^-1.Average ETS/R ratios for single species for two lifestages ranged from 1.0 to 2.5.     

Sexual reproduction in Daphnia: interspecific differences in a hybrid species complex

To investigate whether reproductive variation in the Daphnia galeata-cucullata-hyalina hybrid species complex can explain the occurrence of hybrids and backcrosses, a total of 43 clones from three north German lakes were tested for allocation to sexual reproduction under equal stress conditions. Six replicates per clone were followed until the seventh adult instar. I used the following cues to promote sexual reproduction: short photoperiod, water from a crowded Daphnia culture, fish-conditioned water and low food concentration. For each animal, clutch size and clutch sex were recorded. Ephippia, which were empty since the animals were cultured individually, were only produced by D. cucullata and D. cucullata x hyalina (26% and 6% of the broods, respectively), whereas almost all taxa produced males (the range was 2–15%). Intraspecific variation for male and ephippial production was also found. The fact that the taxa tested show different responses to the stimuli of-fered may indicate that there is reproductive isolation between them. This is supported by field data from the Tjeukemeer (The Netherlands) which shows that D. galeata mostly produces ephippia in spring and D. cucullata in autumn. The presence of hybrids with ephippia in both seasons, however, shows that backcrossing is also possible.     

Population dynamics and production of Daphnia hyalina Leydig and Daphnia cucullata Sars in Tjeukemeer

As part of a research programme on the food chains in Tjeukemeer, the Daphnia hyalina and Daphnia cucullata populations were studied for three successive years. To analyse the factors regulating the production of these two species, their population parameters (density, size distribution, fecundity) and population dynamics (birth rate, mortality rate) were studied and related to environmental factors. Since Daphnia in Tjeukemeer shows continuous recruitment, the population dynamics model INSTAR was developed and used to integrate field data with laboratory data on development rates and length-weight relationships. The dynamics of the Daphnia species are mainly regulated by temperature and fish predation, the latter affects both birth rate and mortality. Total annual Daphnia production was 3.1–6.9 g org. dry wt M^–2, and annual P/B ratio ranged from 25 to 40 for D. cucullata and from 45 to 49 for D. hyalina.     

The crustacean zooplankton of Mali (West Africa)

48 species of Phyllopoda, 24 species of Copepoda, and a freshwater shrimp are reported from Mali. Morphologically noteworthy or little known species are figured. Daphnia barbata and D. dolichocephala are redescribed. Three West-African species of Tropodiaptomus were found. T. senegambiae is synonymised with T. banforanus. Thermodiaptomus yabensis is fully figured. The distribution of T. yabensis and the regional Tropodiaptomus is discussed. A general biogeographical discussion is not yet possible, because for many species, and particularly Cladocera, both taxonomical position and chorological records are fragmentary and uncertain. At least 29 species, however, seem to be restricted to Africa, and some even to West Africa.The water chemistry of the lakes of central Mali is characterized by a low mineral content, but seems not to be distributive to any of the numerous zooplankton species encountered.The zooplankton communities, especially in the lakes of the internal delta of the Niger, are typically composed of numerous species. Among copepods, it is usual to find three or four genera to co-occur, and each genus may be represented by up to three species. This indicates long-term instability of the communities, and suggests strong interspecies competition to be present. This is corroborated by an analysis of the ranges of some African endemics.It is shown that the Niger delta is part of the biological boundary of the Sahara as far as aquatic invertebrates are concerned. West African equatorial climate endemics (e.g. 3 Tropodiaptomus species, Thermodiaptomus yabensis), and arid to semi-arid climate endemics (Daphnia barbata, D. longispina, Metadiaptomus mauretanicus) meet and interpenetrate each others' ranges over a short distance.     

Larval and post-larval development of the branchiopod clam shrimp Cyclestheria hislopi (Baird, 1859) (Crustacea, Branchiopoda, Conchostraca, Spinicaudata)

The larval and post-larval development of Cyclestheria hislopi is examined by SEM. There are at least nine stages (excluding the adult) – six larval and three post-larval stages. The first four stages are passed within the egg-membrane. The larval and the post-larval phase are separated by a profound change in morphology that takes place between stages VI and VII. The larva shifts from a dorso-ventrally flattened 'larval' appearance up to stage VI to a laterally flattened, more 'adult' appearance from stage VII. New morphological data have been revealed by this study, including (1) a large and globular larval dorsal organ; (2) the carapace starts its development from the segments of the first and second maxillae; (3) the anterior ramus of the second antenna in adult Cyclestheria hislopi is the endopod, and the posterior ramus the exopod. Direct development of the brood in Cyclestheria hislopi – unique among conchostracans – is compared with that of the Cladocera. If Cyclestheria is the sister group to the Cladocera, as favoured in this work, the classical neoteny theory of the Cladocera must be reconsidered, as there is no particular similarity between any adults of the Cladocera and any of the larval stages of Cyclestheria . It is suggested that Cyclestheria displays the type of development present in a cladoceran ancestor. A comparison between Cyclestheria and the Upper Cambrian 'Orsten' fossil Rehbachiella kinnekullensis reveals a remarkable similarity in the endite morphology of the trunk limbs.     

Qualitative and quantitative structure,diversity and fluctuations in abundance of zooplankton in Lake Xolotlán (Managua)

The qualitative and quantitative structure of the zooplankton community was studied in 11 localities of Lake Xolotlan (Managua). Twelve rotifers, 4 cladoceran and 5 copepods species were identified. Community diversity (Shannon-Wienerindex) is low,viz. 0,83–2.20. At all times, copepods were the most abundant group. Rotifer densities were higher in zones influenced by rivers and organic pollution. Cladocerans were permanently present in low densities. Climatic events (rainfalls and dry periods) determined population fluctuations of the main zooplankton groups.