Diaphanosoma Brachyurum Research Articles

The role of macroinvertebrates and fish in regulating the provision by macrophytes of refugia for zooplankton in a warm temperate shallow lake

Summary1. The zooplankton often undergoes diel horizontal migration (DHM) from the open water to the littoral of shallow lakes, thus avoiding predators in the former. This behaviour has functional impacts within the lake, as it enhances zooplankton survival, increases their control of phytoplankton and tends to stabilise the clear water state. However, most of the evidence supporting this migration pattern comes from cold north temperate lakes, and more evidence from tropical and subtropical areas, as well as from southern temperate areas, is needed.2. We conducted a field study of the diel horizontal and vertical migration of zooplankton, and the horizontal distribution of potential predatory macroinvertebrates and fish, over two consecutive days in the summer in a temperate lake in the southern hemisphere. We took zooplankton samples at two depths, at three sampling stations (inside beds of aquatic macrophytes, at their edge and in open water) along three transects running from the centre of a bed of Ceratophyllum demersum to open water. At each sampling station, we also took samples of macroinvertebrates and fish and measured physical and chemical environmental variables.3. Zooplankton (pelagic cladocerans, calanoid copepods and rotifers) avoided the shore, probably because of the greater risk from predators there. Larger and more vulnerable cladocerans, such as Diaphanosoma brachyurum and Moina micrura, were two to four times more abundant in open water than at the edge of or inside beds of macrophytes, respectively, by both day and night. Less vulnerable zooplankton [i.e. of medium body size (Ceriodaphnia dubia) or with the ability to swim fast (calanoid copepods)] were distributed evenly between open water and the edge of the plant beds. Small zooplankton, Bosmina huaronensis and pelagic rotifers, showed an even distribution among the three sampling stations. Accordingly, no DHM of zooplankton occurred, although larger organisms migrated vertically inside C. demersum stands.4. Macrophytes contained high densities of predatory macroinvertebrates and fish. The predator assemblage, composed of large‐bodied macroinvertebrates (including odonates and shrimps) and small littoral fish, was permanently associated with submerged macrophytes. None of these groups moved outside the plant beds or changed their population structure (fish) over the diel cycle.5. Submerged macrophyte beds do not represent a refuge for zooplankton in lakes where predators are numerous among the plants, implying a weaker top‐down control of phytoplankton biomass by zooplankton and, consequently, a more turbid lake. The effectiveness of macrophytes as a refuge for zooplankton depends on the associated assemblage of predatory macroinvertebrates and fish among the plants.

Cladoceran community responses to biomanipulation and re‐oligotrophication in Lake Vesijärvi, Finland, as inferred from remains in annually laminated sediment

Summary1. We studied the role of zooplankton in biomanipulation and the subsequent recovery phase in the Enonselkä basin of Lake Vesijärvi, using subfossil cladocerans in annually laminated sediment. Measures to restore the Enonselkä basin included reduction in external nutrient loading and mass removal of plankti‐ and benthivorous fish. Water clarity increased and the lake changed from a eutrophic to a mesotrophic state. However, some signs of increased turbidity were observed after 5–10 years of successful recovery.2. Annual laminae in a freeze core sample were identified and sliced, based on the seasonal succession of diatoms. Cladoceran remains and rotifer eggs were counted, and Daphnia ephippia and Eubosmina and Bosmina ephippia and carapaces were measured. Annual changes in pelagic species composition were studied with principal component analysis. Individual species abundance, size measurements and various cladoceran‐based indices or ratios (commonly used to reconstruct changes in trophic state and fish predation) were tested for change between four distinct periods: I (1985–1988) dense fish stocks, poor water quality; II (1989–1992) fish removal; III (1993–1997) low fish density, improved water quality; IV (1998–2002) slightly increased fish density and poorer water quality.3. After the removal of fish, the mean size of Daphnia ephippia and Eubosmina crassicornis ephippia and carapaces increased significantly. In contrast, the percentage of Daphnia did not increase. When based on ephippia, the ratio Daphnia/(Daphnia + E. crassicornis) increased, but the interpretation was obscured by the tolerance of fish predation by small Daphnia and by the fact that bosminids were the preferred food of roach. Moreover, ephippial production by E. crassicornis decreased in recent years.4. The abundance of Diaphanosoma brachyurum and Limnosida frontosa increased significantly after the fish population was reduced, while that of Ceriodaphnia and rotifers decreased.5. The expanding littoral vegetation along with improved water clarity was clearly reflected in the concentration of littoral species in the deep sediment core. The species diversity index for the entire subfossil community also increased.6. The period of faltering recovery was characterised by greater interannual variability and an increased percentage of rotifers. Nevertheless, the mean sizes of Daphnia ephippia and E. crassicornis ephippia and carapaces indicated a low density of fish. The deteriorating water quality was apparently related to multiple stressors in the catchment after rehabilitation, such as intensified lakeshore building, as well as to exceptional weather conditions, challenging the management methods in use.

Zooplankton composition in a gravel pit lake invaded by the Ponto-Caspian mysid Hemimysis anomala G.O. Sars 1907

During a zooplankton monitoring program in the Rhine catchment (Southern Germany) during the 2006 sampling year, we recorded the mysid Hemimysis anomala in an oligotrophic gravel pit lake. The crustacean and rotifer abundance in the lake was low; maximum density was 28 and 145 ind. L -1 , respectively. Crustaceans were dominated by copepods, which constituted 90- 100% of the zooplankton community. Cladocerans were represented only by Diaphanosoma brachyurum. Rotifers were dominated by Polyarthra spp. for most part of the year. We suggest that the reason for the lack of cladocerans (except Diaphanosmoma) could be competition and/or predation by H. anomala. That D. brachyurum could persist in the presence of Hemimysis may be a result of spatial segregation. Possibly, due to differences in thermal preferences, H. anomala avoids the warm epilimnion of the lake in summer while Diaphanosoma may prefer it.

Microbial activities accompanying decomposition of cladoceran and copepod carcasses under different environmental conditions

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 57:89-100 (2009) - DOI: https://doi.org/10.3354/ame01331 Microbial activities accompanying decomposition of cladoceran and copepod carcasses under different environmental conditions Kam W. Tang1,*, Samantha L. Bickel1, Claudia Dziallas2, Hans-Peter Grossart2 1Virginia Institute of Marine Science, 1208 Greate Road, Gloucester Point, Virginia 23062, USA 2Leibniz Institute of Freshwater Ecology and Inland Fisheries, Alte Fischerhuette 2, 16775 Stechlin, Germany *Email: kamtang@vims.edu ABSTRACT: Cladoceran and copepod carcasses in both marine and freshwater environments represent concentrated reservoirs of organic substrates for water column bacteria. We studied the microbial abundance, activities, and diversity associated with decomposing carcasses of different zooplankton species over short and long time scales, and in oligotrophic vs. eutrophic environments. Fresh carcasses of Daphnia cucullata, Diaphanosoma brachyurum, and Eudiaptomus gracilis were rapidly colonized by bacteria, which reached peak abundances within 1.5 d at 20°C and then decreased. Cell-specific exoenzymatic activity on protein and lipid analogs and production rate of bacteria associated with the carcasses were all higher than in the ambient water. ANOSIM analyses of DGGE banding patterns revealed that bacterial communities associated with both cladoceran and copepod carcasses rapidly diverged from the initial bacterial community in the ambient water. The high similarity of bacteria on both types of carcasses indicates that the carcasses were decomposed by similar bacterial groups. Estimated carcass decomposition rate was lower at 6°C, with an estimated Q10 of 2.4. Carcasses suspended in the eutrophic Lake Dagow had a higher average carbon loss rate than those suspended in the oligotrophic Lake Stechlin. Cladoceran carcasses were initially colonized by bacteria faster than copepod carcasses in both laboratory and field experiments, suggesting that cladoceran carcasses were more prone to exploitation by bacteria, yet copepod carcasses lost carbon at higher rates. Overall, our results suggest that pelagic zooplankton production can be directly converted to water column bacterial production via carcass decomposition, especially during the mid-summer zooplankton decline commonly observed in lakes. KEY WORDS: Decomposition · Exoenzymes · Bacterial production · Bacterial community composition · Zooplankton carcasses Full text in pdf format PreviousNextCite this article as: Tang KW, Bickel SL, Dziallas C, Grossart HP (2009) Microbial activities accompanying decomposition of cladoceran and copepod carcasses under different environmental conditions. Aquat Microb Ecol 57:89-100. https://doi.org/10.3354/ame01331 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 57, No. 1. Online publication date: September 18, 2009 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2009 Inter-Research.

Macrophytes as refuge or risky area for zooplankton: a balance set by littoral predacious macroinvertebrates

Summary1. Zooplankton use macrophytes as day‐time refuge areas when trying to escape from pelagic predators. But macrophytes can also host a diverse and abundant macroinvertebrate assemblage and zooplankton are also likely to face predacious macroinvertebrates once they enter the littoral zone. This study aimed to elucidate the role of macroinvertebrates in determining the refuge capacity of macrophytes.2. We conducted a field enclosure experiment using plastic bags and complementary laboratory feeding trials to test how macroinvertebrates counteract the benefits to zooplankton of the macrophyte refuge. The field experiment consisted of three treatments with different macroinvertebrate assemblages: without predators (WP), low abundance and diversity (LAD) and high abundance and diversity of predators (HAD – which represents lake conditions).3. Populations of Diaphanosoma brachyurum, Bosmina huaronensis and Moina micrura (Cladocera) and of both male and female Notodiaptomus incompositus (Copepoda, Calanoida) declined (by nearly 80%) in the presence of HAD in comparison to WP and LAD treatments.4. Feeding trials revealed that Buenoa sp. (backswimmer), adults of Palaemonetes argentinus (grass shrimp) and Cyanallagma interruptum (damselfly) had a significant negative impact on cladocerans (D. brachyurum, B. huaronensis) and the calanoid copepod population (males, females and copepodites). These predators showed a strong predation effect ranging from 75% to 100% reductions of zooplankton populations.5. The refuge effect offered by macrophytes to zooplankton depends on and is balanced by the predacious macroinvertebrate assemblage that plants host. The risk of confronting littoral predators is high and macroinvertebrate presence can turn the macrophytes into risky areas for zooplankton.

Effect of low-level industrial heating on seasonal cycle transformation in cladocerans

We studied effects of a low-level industrial heating caused by heating-electric power station on changes in seasonal adaptations in cladocerans inhabiting the Kama River Reservoir (the Volga River tributary). The biological significance of low-level industrial heating was analyzed by comparison of two stations: one with natural temperatures and another one affected by cooling water from the Kama Heating-Electric Power Station. We found that even relatively low (less than 2°C) difference in seasonal temperature between these two stations resulted in changes of reproductive mode in the most abundant species of Cladocera (Bosmina longirostris (Muller, 1785), Daphnia longispina Muller, 1785, and Diaphanosoma brachyurum sensu lato). At station with low heating, all species of cladocerans had some negative changes in their seasonal life cycles (sex proportion, resting egg production etc) with following disturbances in their over-wintering adaptations. Our results on early appearance and increasing of male proportion in population structure caused by industrial heating can be used for assessment of negative consequences of low-level industrial heating and global climate changes. With help of modeling, these data can be used for creation a new methods of prognosis both in global and local scales. It was finally resumed that low-level industrial heating, similar in scale to those observed during last decades under climate changes, leads to significant declining in population density and productivity in dominant species of cladocerans.

Population dynamics of Daphnia longispina (O.F. Müller, 1785) and Diaphanosoma brachyurum (Lievin, 1848) (Crustacea, Cladocera) under stable and graded temperature regimes

Laboratory experiments have been performed to study the effects of different temperature regimes-constant (16.3 +/- 0.8, 20.3 +/- 0.8, and 24.6 +/- 0.7 degrees C) and graded, with temperatures changing at intervals of 4.4 or 8.8 degrees C within the range of 15.1-25.4 degrees C--on the population dynamics of two dominant species of littoral zooplankton, Daphnia longispina and Diaphanosoma brachyurum. The results show that aperiodic stepwise changes in temperature within the ranges of 16.3-20.4, 20.4-25.1, and 16.3-25.1 degrees C, which may take place in water bodies of the temperate zone in the summer period, can exert either stimulating (direct or delayed) or inhibitory effect on the natural development of D. longispina populations. The development of D. brachyurum, a more stenothermic thermophile, is stimulated only by a stable elevated temperature (24.5 +/- 0.9 degrees C). All temperature changes within the above range, except for rapid heating from 16.3 to 25.1 degrees C, either inhibit the development of D. brachyurum populations or have no significant effect on them.

Absence of typical life-history trade-offs in the cladoceran, Diaphanosoma brachyurum (Lievin, 1848) — the role of fish predation in a temperate lake (eastern Poland)

Life-history trade-offs can be defined as the beneficial side-effects of a species' evolutionary reaction that has the purpose of solving problems caused by environmental constraints. In this study, the life-history trade-offs of the dominant cladoceran, Diaphanosoma brachyurum (Lievin, 1848) were studied in Lake Piaseczno (Poland). Size at maturity (SAM), the proportion of ovigerous females, brood size, and the depth-selection behaviour of D. brachyurum were determined. The contribution of D. brachyurum and of other cladocerans to the diet of fish was also quantified. The investigation showed that fecundity was low, and that the species did not perform diel vertical migrations. The results obtained further indicate that D. brachyurum, in contrast to other cladocerans recorded from the lake, was not affected by fish predation, as the fish appeared to ignore this species. Thus, although D. brachyurum did not exhibit any apparent life-history trade-offs, it must have profited from fish predation pressure reducing the density of competitive cladoceran populations, which might well be indicated by the fact that D. brachyurum densities rose in correlation with an increased predation pressure of fish in early summer, on (a significant part of) the remaining species of cladocerans. Les compromis de traits d'histoire de vie peuvent etre definis comme des effets secondaires benefiques de la reaction evolutive d'une espece dont le but est de resoudre les problemes poses par des contraintes environnementales. Dans cette etude les compromis de traits d'histoire de vie du Cladocere dominante Diaphanosoma brachyurum (Lievin, 1848) ont ete etudies dans le lac Piaseczno (Pologne). La taille a la maturite (SAM), la proportion de femelles ovigeres, la taille de la ponte et le comportement de selection de la profondeur de D. brachyurum ont ete determines. La contribution de D. brachyurum et d'autres Cladoceres au regime alimentaire des poissons a aussi ete quantifiee. Les recherches montrent que la fecondite etait basse et que les especes n'effectuent pas de migrations verticales journalieres. Les resultats obtenus indiquent que D. brachyurum, contrairement aux autres Cladoceres trouves dans le lac, n'a pas ete affecte par la predation par les poissons, car les poissons semblent ignorer cette espece. Ainsi, alors que D. brachyurum ne presente aucun apparent compromis de traits d'histoire de vie, elle a du beneficier de la pression de predation par les poissons reduisant la densite des populations des autres Cladoceres en competition; ce qui semble indique par le fait que les densites de D. brachyurum s'elevent en correlation avec l'augmentation de la pression de predation par les poissons en debut d'ete sur (une partie significative) des autres especes de Cladoceres.

Predation follows competition in depth selection behaviour of Cladocera in a deep lake (E Poland)

Predation follows competition in depth selection behaviour of Cladocera in a deep lake (E Poland) Observations of the vertical distribution of Cladocera in the pelagic zone of the deep Lake Piaseczno (38.8 m) focused on 6 species: Diaphanosoma brachyurum, Daphnia longispina, D. cucullata, Bosmina coregoni, B. longirostris, and Chydorus sphaericus. The animals displayed clear depth preferences, and their migration patterns were limited to small depth amplitudes. The results show that vertical habitat segregation of cladocerans in the lake consists mostly in the mechanism of competition for accessible food resources, rather than in the mechanism of predation avoidance.

Crustacean plankton of restored Lake Starodworskie

Lake Starodworskie is a reservoir restored since the 1960s, first through artificial aeration and in the 1990s by the method of phosphorus inactivation. Studies of zooplankton were conducted in 2007–2008. The aim of the present research was to analyze and evaluate the taxonomic structure and overall abundance of the crustacean plankton of the lake. The eudominant species found were: Bosmina longirostris and Daphnia cucullata, while the dominant species included: Eudiaptomus graciloides, Diaphanosoma brachyurum and Mesocyclops leuckarti. The average annual density of Crustacea in the reservoir amounted to 329 indiv. dm−3, while the average biomass reached 5.1mg dm−3. The abundance of indicatory species typical for eutrophic waters was smaller than recorded during previous zooplankton studies of Lake Starodworskie (average densities were: M. leuckarti – 12 indiv dm−3, T. oithonoides – 4 indiv dm−3, D. brachyurum – 14 indiv dm−3, B. longirostris – 92 indiv dm−3). The overall abundance of the zooplank ton and its structure suggest moderate eutrophy of the reservoir.

Spatio-Temporal Segregation of Cladocerans within a Chara hispida Bed

ABSTRACT I examined the diel abundance of cladocerans in the vertical and horizontal profiles through a Chara hispida stand and adjacent open water areas in Lake Wielkowiejskie. The total abundance of cladocerans differed significantly between the stations with the middle part of the stonewort bed having the lowest densities (irrespective of time). Single species differences were recorded for Bosmina longirostris, Ceriodaphnia quadrangula, and Diaphanosoma brachyurum. Total cladoceran abundance at night differed significantly from that observed during the day (irrespective of sampling site); in the central part of the stonewort stand, the highest densities occurred in the early morning, while all other zones had highest densities at night. Single species (Alona costata, Alonella exigua, Bosmina coregoni, B. longirostris, Ceriodaphnia pulchella, C. quadrangula, Chydorus sphaericus, and D. brachyurum) differed mostly with regard to dusk vs. morning or night. Even though the distances between the sampling stations were less than 0.5 m, a classical zooplankton abundance distribution for lakes with fish pressure was observed on a microscale, in terms of both vertical and horizontal profiles within the stonewort bed and the adjacent zones of open water. Chlorophyll a, conductivity, pH, and dissolved oxygen were correlated with diel cladoceran distribution.

Distribution du zooplancton dans les lacs à climat méditerranéen

The sometimes sharp thermal variations and irregular precipitations and force concentrated over short periods characterize the Mediterranean climate. The structure of the zooplanktonic settlement was analyzed during one year in three Algerian reservoirs (lakes) with different geographical and climatic situation, in relation to abiotic factors (temperature, dissolved oxygen, pH, suspended matter, carbonates, nitrogenized and phosphorated nutritive salts). A canonical correspondence analysis was used to estimate the influence of the abiotic factors on the temporal distribution.The studied lakes are located, on the one hand, in northern Algeria, in a sub-humid area (Lake Boukourdane) and, on the other hand, in the South of the country, in the arid region (Foum El Ghorza and Djorf Torba). Analysis of the environmental parameters indicates that there is a seasonal variation in the three reservoirs. In Lake Foum El Ghorza, the temperature and hydrology variations, linked with the arid climate, affects the concentration of dissolved oxygen, which strongly decreases (1.5 mg/l), involving a pH reduction; suspended matters are sometimes high, coming from the stripped catchment area, causing a turbidity in this not very deep lake. The study of the distribution of the species allowed us to highlight a seasonal temporal variation. Lake Boukourdane, in the sub-humid zone, has an increased specific richness ( SR = 13 ) . The various species evolve in alternation during the annual cycle. The representative species of this lake is Copidodiaptomus numidicus, characteristic of the rainy and endemic zone of the western Mediterranean; it is dominant (67%) in the spring. The Stenothermal species Diaphanosoma brachyurum, endemic of hot waters, is common to the two lakes; it evolves particularly in the summer (51.3%) at Boukourdane, whereas it is perennial and dominant (55%) in the spring at Djorf Torba. The specific richness is lower in Djorf Torba ( SR = 7 ) and in Foum El Ghorza ( SR = 6 ) . The species collected in these two lakes are common and cosmopolitan, but they are adapted to the extreme conditions of the arid climate. Nevertheless, the species evolving in Lake Foum El Ghorza have undergone a significant decline, which has reduced the number of species and their density in the summer–autumn period. Thus, we can say that in the studied lakes, the hydrological factors and the temperature related to the Mediterranean climate would be two of the principal causes of the temporal distribution of the species. To cite this article: M. Cherbi et al., C. R. Biologies 331 (2008).

English

  Accumulation of heavy metals (Cd, Pb, Hg, Cr) in water and plankton of Sarıyar Dam Lake (SDR) was seasonally studied from April, 2000 to December, 2004. In addition, seasonal changes in phytoplankton and zooplankton populations and species abundance were also determinate. Some physio-chemical parameters of water and their correlation with heavy metals were also determinated. The dominant phytoplanktonic algae determined were Choroococcus, Gomphospheria, Oscillatoria, Phormidium, Anabaena, Nostoc, Cystodinium, Dinobryon, Ankistrodesmus, Chlorella, Coelastrum, Oocystis, Pediastrum, Scenedesmus, Cosmarium, Oedogonium, Cyclotella, Achnanthes, Amphora, Anomoneis, Cocconeis, Cymbella, Diatoma, Diploneis, Fragilaria, Gomphonema, Navicula, Nitzschia, Nitzschia, Rhoicosphenia, Surirella andSynedra. The dominant zooplanktonic organisms determined were Asplachna priodonta, Brachionus angularis, Keratella quadrata, Keratella cochlearis, Keratella tropica, Polyarthra vulgaris, Proales decipiens, Bosmina longirostris, Ceriodaphnia quadrangula, Chydorus sphaericus, Daphnia longispina, Diaphanosoma brachyurum, Macrothrix laticornis, Acanthocyclops robustus andAcanthodiaptomus denticornis. High concentrations of all heavy metals were recorded in the plankton. Hg was lowest and Pb highest; but the concentration of each metal varied seasonally.   Key words: Heavy metals, accumulation, water pollution, algae, zooplankton.

Horizontal and seasonal patterns of tropical zooplankton from the eutrophic Prado Reservoir (Colombia)

Zooplankton community analyses can reveal valuable information about the trophic status and secondary production in reservoirs. The zooplankton seasonal distribution and important physical and chemical parameters in Prado Reservoir (Tolima, Central Colombia) were studied in monthly surveys throughout a hydrological cycle (February 2000–January 2001) in order to establish seasonal patterns and the biotic and abiotic relationships for the reservoir. Surface zooplankton collections at 1 m depth were taken at six sampling stations with regard to reservoir morphometry, location of main tributaries and mixing areas of the incoming tributaries. Cladocerans numerically dominated (48.1%) the community throughout the study period followed by Copepoda (32.7%), Rotifera (19.1%), and Diptera larvae (0.01%). Among the cladocerans, there was a greater abundance of Bosmina longirostris (69.8%) than other crustaceans. Among the Rotifera, Brachionus falcatus was the most abundant with 23% and Keratella tropica was least abundant with 8%. The only cyclopoid species found was Thermocyclops decipiens. The phantom midge Chaoborus sp. was also part of the zooplankton community. Based on numbers, cladocerans represented a significant component of the zooplankton in both dry and rainy seasons. Four species ( Brachionus spp., K. tropica, Diaphanosoma brachyurum, Ceriodaphnia cornuta, Moina sp., and T. decipiens) had never previously been found in the reservoir, but were recorded for other standing Colombian water bodies. The replacement of B. longirostris instead of Daphnia sp. as dominant species was observed. The results of the comparison of the different studies confirmed that the trophic state of this artificial lake may be classified as eutrophic, and in general, physical, and chemical homogeneity were observed both spatially and temporally.

Midsummer heat wave effects on lacustrine plankton: Variation of assemblage structure and fatty acid composition

The effects of the 2003 European heat wave on a freshwater plankton assemblage and its fatty acid (FA) composition were investigated. Composition and FA profiles of four size categories of planktonic organisms collected in 2003 were compared to those of the colder year 2002. Temperature affected plankton population selecting thermophilic ones and had direct and indirect effects on its nutritional quality given by its FA patterns. Among algae, Ceratium hirundinella dominated and occurred at higher temperatures than described in the literature. Cyanobacteria showed a limited development. Diaphanosoma brachyurum was the dominant zooplanktonic species. Thermal environment appeared to favour the dominance of cladocerans and a decline in copepods abundance with cyclopoids ( Acanthocyclops robustus) favoured over calanoids. Variation of FA composition with temperature was reflected in the relative proportion of saturated FA (SAFA), monounsaturated FA (MUFA) and polyunsaturated FA (PUFA). Organism exposure to overheated water resulted in increased SAFA and MUFA content at the expense of PUFA. This effect can be promoted in phytoplankton with high light intensity and sunshine duration.

Feeding of 0+ smelt Osmerus eperlanus in Lake Peipsi

INTRODUCTION Smelt Osmerus eperlanus (L.) is the main zooplanktivorous fish species in Lake Peipsi and is so an important predator on zooplankton and large invertebrates in this lake. Smelt is zooplanktivorous at younger ages, gradually shifting to larger invertebrates during growth, and the oldest and largest smelts are piscivorous (Karjalainen et al., 1997; Vinni et al., 2004). When smelt start feeding, the number of suitable food organisms available is critical for fish survival. Rotifers and crustacean zooplankton (cladocerans and copepods) are important food items during the first summer because the mouth width seems to be the critical determinant of the ability of smelt to handle large food items (Strelnikova & Ivanova, 1983; Naesje et al., 1987). Phytoplankton can also be important as an initial food item for newly-hatched smelt larvae, as found in Norwegian Lake Mjosa by Naesje et al. (1987). Later, from mid-summer to autumn, age-0 smelt in Lake Mjosa feed mainly on copepods and cladocerans, with no strong preference for either of these groups (Naesje et al., 1987). In the Kuronian Lagoon (coastal waters of the Baltic Sea), young smelt prefer cladocerans from June to September, copepods in September, and cladocerans after that (Vashkevichiute, 1959). In Finnish lakes, age-0 smelt feed mainly on copepods, sometimes on cladocerans, most often in proportion to their availability in the plankton (Sterligova et al., 1992; Karjalainen et al., 1997). Earlier research on smelt feeding in Lake Peipsi and in Lake Pihkva (Tikhomirova, 1974) showed that smelt larvae feed mainly on cladocerans (Bosmina, Chydorus, Daphnia cucullata, and Diaphanosoma brachyurum, occasionally Leptodora and Sida) and copepods (Diaptomus, Cyclops, Mesocyclops) during the spring-summer period. In June and July, chironomid larvae and adult insects become more important, and smelt of 6.9 cm and longer feed mainly on fish larvae. The results of Vashkevichiute (1959) from the Kuronian Lagoon also showed that chironomids are the main smelt food in mid-summer. Chironomids are often consumed by older smelt, from the second summer onwards. Data on the feeding behaviour of the fish in Lake Peipsi are scarce, and far from sufficient for understanding the functioning of the food web in this lake. The aim of the present study was to analyse the diet of smelt in Lake Peipsi. The food eaten was also compared with the food available in the lake. STUDY SITE, MATERIAL, AND METHODS Lake Peipsi (3558 [km.sup.2]) is located in eastern Estonia, on the border of Estonia and Russia. It consists of three parts: lakes Peipsi s.s., Lammijarv, and Pihkva. The present paper deals with Lake Peipsi s.s. It is a moderately eutrophic polymictic lake with a mean depth of 8.3 m, average concentrations of total phosphorus 40 mg P [ms.up.-3] and total nitrogen 700 mg N [m.sup.-3] (Noges et al., 2008). Descriptions of the phyto- and zooplankton of Lake Peipsi are given by Laugaste et al. (2001) and Haberman (2001), respectively. Lake Peipsi provides a great variety of biotopes with a diverse trophic state. As a result of this the flora and fauna of this lake are quite rich both in the number of species and in their abundance. Lake Peipsi can be considered a large water body of quite high productivity. The biomass of phytoplankton has fluctuated from 1 to 125 g [m.sup.-3] and the mean biomass of zooplankton (in summer) is 3.1 g [m.sup.-3]. The fish catches have usually been 8000-11 000 t or 22-31 kg [ha.sup.-1] [yr.sup.-1] since the 1930s. The main commercial fishes in the lake are smelt, pikeperch, perch, bream, pike, ruffe, roach, and until the early 1990s also vendace. Smelt samples were collected in summer and autumn 2003 with a bottom trawl (height 3 m, width 18 m, 10 mm knot-to-knot mesh size at cod-end) once a month from July to November. The samples were collected at 58[degrees]42.227N, 27[degrees] 17.653E after previous monitor trawling. …

Crustacean zooplankton distribution patterns and their biomass as related to trophic indicators of 29 shallow subtropical lakes

A comparative limnological study was carried out to present a snapshot of crustacean zooplankton communities and their relations to environmental factors to test whether there is a consistent relationship between crustacean biomass and trophic indicators among lake groups with similar trophic conditions. The study lakes showed a wide range of trophic status, with total phosphorus (TP) ranging from 0.008 to 1.448 mg L −1, and chlorophyll a from 0.7 to 146.1 μg L −1, respectively. About 38 species of Crustacea were found, of which Cladocera were represented by 25 taxa (20 genera), and Copepoda by 13 taxa (11 genera). The most common and dominant species were Bosmina coregoni, Moina micrura, Diaphanosoma brachyurum, Cyclops vicinus, Thermocyclops taihokuensis, Mesocyclops notius and Sinocalanus dorrii. Daphnia was rare in abundance. Canonical correspondence analysis showed that except for four species ( D. hyalina, S. dorrii, C. vicinus and M. micrura), almost all the dominant species had the same preference for environmental factors. Temperature, predatory cyclopoids and planktivorous fishes seem to be the key factors determining species distribution. TP was a relatively better trophic indicator than chlorophyll a to predict crustacean biomass. Within the three groups of lakes, however, there was no consistent relationship between crustacean biomass and trophic indicators. The possible reason might be that top-down and bottom-up control on crustaceans vary with lake trophic state. The lack of significant negative correlation between crustacean biomass and chlorophyll a suggests that there was little control of phytoplankton biomass by macrozooplankton in these shallow subtropical lakes.

Feeding habits of sand smelt (Atherina boyeri, Risso 1810) in Trichonis Lake (Western Greece)

Summary The feeding habits of sand smelt (Atherina boyeri, Risso, 1810) from Trichonis Lake (Western Greece) were investigated. Stomach contents were analyzed from 240 specimens with total lengths ranging from 35 to 112 mm. Samples were taken at monthly intervals (January–December 1997). Of the total number of stomachs examined, 53 were empty (22.1%). However, values varied greatly with season (maximum in January: 50%; minimum in August: 7.6%). Prey analyses of stomach contents identified 15 important items (%Rn > 0.05) belonging to six major groups: crustacean (copepods, cladocera), mollusca (bivalve: larvae), insects (larvae), cestode worms and finfish (fry and eggs). Dominant prey were larvae of the bivalve Dreissena polymorpha (%Rn = 33.8), the copepods Eudiadomus drieschi (%Rn = 26.4) and the cladocera Diaphanosoma brachyurum (%Rn = 24.2). The importance of cladocera and copepods decreased with increasing size of the sand smelt, while the importance of bivalve larvae, fish eggs and finfish fry increased with increasing sand smelt size. Seasonal changes in diet composition and prey abundance in sand smelt stomachs were recorded as coinciding with the seasonal composition and abundance of the zooplankton community in the surface layers of Trichonis Lake. Bivalve larvae were the dominant prey of A. boyeri during January to May, while copepods and cladocera dominated from June to December.

In situ assays with tropical cladocerans to evaluate edge-of-field pesticide runoff toxicity

Tropical regions' economy is usually based on agriculture, which involves an intensive use, and even frequent overuse, of pesticides. Nevertheless, not much research has been done on the impact of pesticides on tropical aquatic ecosystems, which are often contaminated by runoff-related pesticide inputs due to unpredictable and torrential rainfalls. This study aimed to: (i) adapt and evaluate a short-term sublethal in situ assay using post-exposure feeding as an endpoint, to the tropical cladoceran species Diaphanosoma brachyurum (collected at the Pedra do Cavalo dam in the Paraguaçu River basin, Bahia, Brazil), and, (ii) assess the role of the standard species Daphnia magna as an adequate laboratory surrogate. Lethal and sublethal (post-exposure feeding) responses were assessed for the two species. To evaluate these responses under environmentally realistic exposure conditions, a runoff event was simulated in an agricultural area previously contaminated with different deltamethrin concentrations. The resultant runoff water was used to set up microcosms with different dilutions, simulating the entrance of runoff water in an adjacent lentic system. An in situ assay with D. brachyurum was performed inside the microcosms, allowing to discriminate the effects due to deltamethrin from those due to other potential stressors associated with the experimental design (e.g. organism handling, load of suspended particles, microcosm design). Water samples were collected from microcosms to conduct a laboratory assay with D. magna. The in situ methodologies revealed to be suitable to conduct assays with D. brachyurum under tropical conditions, since all exposed organisms were successfully retrieved from the chambers. Furthermore, none of the potential stressors associated with the experimental design influenced the daphnids' performance. The tropical cladoceran species, exposed under more realistic conditions, revealed to be more sensitive than the laboratory standard species: lethal effects were only observed for D. brachyurum and sublethal effects were noticed at a lower deltamethrin concentration for this species than for D. magna.

Experimental biological approach to the effects of <i>Microcystis</i> on some cladoceran population in Lake Taihu

微囊藻是形成蓝藻水华最普遍的一种, 不同枝角类受微囊藻的影响不同。实验从太湖梅梁湾分离天然的微囊藻, 研究了其对长刺溞、隆线溞、短尾秀体溞和角突网纹溞四种枝角类存活和生殖的影响。在微囊藻食物浓度为1×10⁶ cells/ ml, 测得四种枝角类的半致死时间(LT₅₀)分别为长刺潘3.03d、隆线溞3.79d、短尾秀体溞8.48d和角突网纹溞9.25d, 体长较小的短尾秀体溞和角突网纹溞的半致死时间相对较长;实验过程中没有观察到长刺溞和隆线溞有新生幼体, 而短尾秀体溞和角突网纹溞在少数几天里产出了少量新生幼体, 以不同浓度微囊藻（0.5×10⁶-8×10⁶cells/ml）喂养枝角类, 测得四种枝角类的24h半致死浓度(LC₅₀)分别为:4.10×10⁶、4.78×10⁶、6.21×10⁶和7.77×10⁶ cells/ml。参照以栅藻喂养的枝角类生长情况, 可知太湖微囊藻对四种枝角类的存活和生殖有很强的负面作用, 其中体长较大的长刺溞和隆线溞受的影响相对较大。;Microcystis is one of the most common and most studied bloom-forming cyanobacteria and a well-known producer of microcystins. Different cladocerans usually exhibited different responses to the toxicity of Microcystis. In the present study, the effects of toxic Microcystis from Lake Taihu were investigated by performing, acute tests on cladocerans (Daphnia longispina, Daphnia carinata, Diaphanosoma brachyurum and Ceriodaphnia cornuta), using crude Microcystis extract. On a diet of Microcysits (1 10⁶ cells/ml), the median lethal time(LT₅₀) of four cladocerans were 3.03、3.79、8.48 and 9.25 days, respectively. The longer LTS0 were recorded for D. brachyurum and C. cornuta which have small size. Among the experiment, there was no new neonates of D. longispina and D. carinata, and few new neonates of D. brachyurum and C. cornuta. The 24h-LC₅₀ of D. longispina, D. carinata, D. brachyurum and C. cornuta were 4.10×10⁶、4.78×10⁶、6.21×10⁶和7.77×10⁶ cells/ml. So, the effects of Microcystis on the survivorship and fecundity of cladoceran population in Lake Taihu were very intense, and the effects of D. brachyurum and C. cornuta which have small size were relatively gently.