武汉东湖主要养殖水域的浮游甲壳动物群落分析

报道了1994－1996年武汉东湖水果湖、郭郑湖、汤林湖和后湖4个主要鱼类养殖水域甲壳动物群落结构变化的调查结果,其目的旨在比较4个湖区甲壳动物群落结构的差异,探讨甲壳动物群落变化与鱼类养殖,水生植物及水体富营养化间的关系,结果表明,在东湖Ⅰ、Ⅱ站,蚤类平均密度明显低于Ⅲ、Ⅳ站（P＜0．05）,而近邻剑水蚤在3个周年里一直占据桡足类的优势地位。Ⅲ站从1995年,Ⅳ站从1996年起,近邻剑水蚤均取代了广布中剑水蚤成为桡足类的第一优势种。甲壳动物的体长频度分布表明,在3个研究中,11－12月份和1－4月份体长大于1mm的甲壳动物频度均显著高于5－10月份,体长大于1mm的枝角类个体数以Ⅲ、Ⅳ站较多,而大于1mm的桡足则以Ⅰ、Ⅱ站较多。     

Characterization of small shallow ponds with color video imagery in Central Mexico

We present a method to evaluate ecological characteristics of small shallow ponds in Central Mexico based on video remote sensing and image processing techniques in a GIS environment. We used a set of color video imagery obtained from heights lower than 700 m above ground. Our analysis established statistical correlations between the average reflectance values contained in video imagery (digital numbers DN per Blue-Green-Red band) and the average values of limnetic variables: (1) water suspended solids concentration; (2) water turbidity; (3) total macrophytes coverage; (4) free floaters and emergent macrophytes coverage; (5) zooplankton abundance; and (6) chlorophyll-a concentration in water. We found strong correlation between DN values and vegetation presence, suspended solids concentration and water turbidity (R= 0.85 to 0.98), but weak correlations with phytoplankton and zooplankton abundance. This cheap and fast method can be used to describe general conditions of ponds related with vegetation abundance, turbidity and suspended solids.     

Biogeography of copepods in lakes and ponds of subarctic Québec,Canada

We aimed to determine whether the copepod assemblages in lakes and ponds of northern Québec, Canada, were closer in composition to those found in southern Québec, or to those reported from the subarctic and arctic. Six calanoid and five cyclopoid species were identified from 37 ponds and lakes located in the region between 55° N and 59° N. Species diversity was generally low, ranging from 0 to 4 species per lake. Dominant species were Leptodiaptomus minutus and Acanthocyclops vernalis. The species assemblages showed high affinity with those found in forested regions of southern Québec. Exceptions were Leptodiaptomus tyrrelli, previously only recorded west of Hudson Bay, and Hesperodiaptomus arcticus, hitherto recorded north of 58° N. Relationships between the lakes, species, and environmental variables were explored using multivariate analysis. Lakes situated along the coast and on two offshore islands clustered together and were characterised by higher conductivity and pH than those lakes located further inland. Leptodiaptomus tyrrelli was common in these coastal lakes. Canonical correspondence analysis revealed statistically significant relationships between copepod distributions and conductivity, dissolved organic carbon and pH. These three variables accounted for 70% of the variation in the species' distribution.     

Zooplankton on the move: first results on the quantification of dispersal of zooplankton in a set of interconnected ponds

In systems of interconnected ponds or lakes, the dispersal of zooplankton may be mediated by the active population component, with rivulets and overflows functioning as dispersal pathways and the dispersal being unidirectional. Such systems offer the possibility to study the impact of dispersal rates on local population dynamics and community structure, and provide opportunities to quantify dispersal in the field in a straightforward manner. In this study, dispersal of active zooplankton populations among interconnected ponds was quantified directly in the field by sampling the small waterways connecting the ponds. The number of dispersing zooplankton sampled in connecting elements was on average high (almost 7000 ind h^–1). However, the contribution of dispersing individuals to total population size in the target ponds was very limited (< 1% 24 h^–1.). Only a weak diel pattern in dispersal rates was observed.     

Horizontal distribution of cladocerans in arctic Greenland lakes – impact of macrophytes and fish

Submerged macrophytes may play an important role as a refuge for zooplankton against predators. However, a recent study suggests that their importance depends on the trophic state of the lake. We studied the impact of fish and macrophytes on the horizontal distribution of pelagic cladocerans in 56 oligotrophic arctic Greenland lakes. In north-east and western Greenland, zooplankton was sampled in the near-shore (littoral) and central (pelagial) part of all lakes and fish were sampled with multiple mesh-sized gill nets. Macrophytes were visually estimated in the littoral. In north-east Greenland, 5 taxa of cladocerans were found, while 14 taxa were recorded in western Greenland. Daphnia pulex occurred only in fishless lakes in both northeast and western Greenland and avoided the near-shore areas in the shallow and deep lakes. Bosmina spp. and Holopedium gibberum were evenly distributed between the littoral and the pelagial in the deep and shallow fishless lakes. However, their near-shore density was lowest in the presence of fish. Macrophyte-related and benthic cladocerans concentrated either in the littoral or were evenly distributed between the littoral and the pelagial, irrespective of depth and fish presence or absence. Macrophytes had no impact on the horizontal distribution of pelagic cladocerans. Thus, it is concluded that horizontal heterogeneity of Bosmina spp. and Holopedium gibberum might be affected by the presence of fish.     

Changes in abundance of the icefish Neosalanx pseudotaihuensis Zhang (Salangidae) and the impact on the zooplankton community of Xujiahe Reservoir,central China

The icefish Neosalanx pseudotaihuensis Zhang is a small and commercially exploited zooplanktivorous fish in Xujiahe Reservoir (central China). Data of catch per unit effort (CPUE) from June 1995 to December 1997 show that the abundance of the icefish varied dramatically, which is reflected in the populations of the dominant cladocerans. The densities of Leptodora kindti, Daphnia galeata and Diaphanosoma dubia were the highest in 1997 when the abundance of the icefish was the lowest, and the reverse was the case for Boimina spp. These results document that the population of this annual fish is very variable and high biomass of the fish could exert a pronounced effect on the zooplankton community.     

New records of Amphipoda Hyperiidea in associations with gelatinous zooplankton

Associations between Amphipoda Hyperiidea specimens and gelatinous zooplankton such as cnidarians, ctenophores or salps are known in the literature. It is well established that many hyperiids are intimately associated with gelatinous zooplankton during part or all of their life-cycles, and that the associations could be of commensal or of parasitic nature, sometimes very highly species-specific. Although conventional net sampling usually does not preserve evidence of these associations, 12 instances of association (I.A.) were found in nine of the 49 samples collected during the 'FINEP XI Cruise', carried out on the Southeast coast of Brazil (23–28 °S), in January 1980. Lestrigonus bengalensisGiles, 1887 (11 specimens) and Simorhynchotus antennarius(Claus, 1871) (one specimen) were found inside salps and siphonophores. The study of the nature of these associations is essential to the understanding of the evolution of the group.     

Temperature impact on the midsummer decline of Daphnia galeata: an analysis of long-term data from the biomanipulated Bautzen Reservoir (Germany)

1. The influence of water temperature on occurrence and duration of a midsummer decline (MSD) of Daphnia galeata was studied in the biomanipulated Bautzen Reservoir in Germany. The proportion of piscivores in the fish community of the reservoir has been enhanced experimentally since 1981. As a consequence, Daphnia galeata has dominated the zooplankton. Over 18 years of study (1981–1998), a long‐lasting MSD (longer than 30 days) occurred in 7 years, whereas a short MSD (shorter than 30 days) was observed in 6 years. During the remaining 5 years, an MSD was not observed.
2. Two hypotheses were examined to explain the observed patterns. First, we postulated that high water temperature during winter and early spring (January–April) leads to an MSD after an early and high spring peak of daphnids. On the other hand, low temperature during winter and early spring should not cause an MSD owing to a slower increase of the population, resulting in a later peak of daphnids. Second, we hypothesized that the mean water temperature during early summer (May and June) influences the occurrence of an MSD (by controlling young‐of‐the‐year (YOY) fish predation on daphnids).
3. The water temperature during winter and early spring explains 83%, and the early summer water temperature 55%, of interannual variation in the occurrence of an MSD.
4. The interannual variation in duration of an MSD was neither explained by temperature during winter and early spring nor by early summer temperature alone, but in 14 of the 18 years (78%) by a combination of both.
5. We conclude that water temperature during winter and early spring had a strong impact on Daphnia mortality by influencing height and timing of the spring peak which, in turn, influenced the extent of overexploitation of their food resources. By contrast, the water temperature during early summer probably influenced the mortality of daphnids caused by predation of YOY fish. The relative timing of both sources of mortality, which depends on the temperature regime during the first 6 months of the year, is the key process in controlling the occurrence and duration of an MSD. A long‐lasting MSD, therefore, is likely in Bautzen Reservoir only if temperatures are high during winter and early spring, as well as during early summer.
6. As a consequence of climate warming, recent climate records reveal warming during winter, spring and early summer in middle Europe, rather than an increase in mean annual temperatures. If our findings and conclusions are related to this regional and temporal pattern of climate warming, an increasing frequency of years with a long‐lasting MSD and, consequently, a decreasing efficiency of biomanipulation can be predicted.     

Drought and aquatic community resilience: the role of eggs and seeds in sediments of temporary wetlands

1. A long‐lived bank of propagules consisting of eggs, seeds and spores is one mechanism that allows aquatic communities to survive drought. A drying (drought) event is, for aquatic organisms in a temporary wetland, a phase from which communities must recover. Such a dry phase is often considered a disturbance but should not be considered adverse or catastrophic for the organisms that have evolved to live in temporarily wet habitats. 2. This paper explores the parallels between the egg bank of zooplankton and the seed bank of aquatic plants as means of survival in temporary wetlands. The resilience of communities in temporary wetland ecosystems is assessed by examining dormancy, hatching, germination, establishment and reproduction of animals and plants from the egg and seed banks of wetlands with a range of wetting and drying regimes. 3. Both the zooplankton and aquatic plants of the temporary wetlands studied rely on their egg and seed banks as a means for surviving drying. These communities recover after the disturbance of drying by means of specific patterns of dormancy, dormancy breakage, hatching, germination, establishment and reproduction. Spatial and temporal patterns of species richness allow resilience through dormancy, as not all species are present at all sites and not all species hatch and germinate at the same time. Multiple generations in the egg and seed bank and complexity of environmental cues for dormancy breakage also contribute to the ecosystem's ability to recover after a drying event. A persistent egg and seed bank allows species‐rich communities to hatch, germinate and develop rapidly once dormancy is broken. Rapid establishment of species‐rich communities that reproduce rapidly and leave many propagules in the egg and seed bank also facilitates community recovery on flooding of a temporary wetland after a drying event. 4. To maintain the diversity of temporary wetland communities through droughts and floods we need to manage the dry and wet phases of wetlands. To conserve a wide range of wetland types, we need to maintain a variety of hydrological patterns across the landscape.     

Effects of experimentally induced cyanobacterial blooms on crustacean zooplankton communities

SUMMARY 1. Large in situ enclosures were used to study the effects of experimentally induced cyanobacterial blooms on zooplankton communities. A combination of N and P was added to shallow (2 m) and deep enclosures (5 m) with the goal of reducing the TN : TP ratio to a low level (∼5 : 1) to promote cyanobacterial growth. After nutrient additions, high biomass of cyanobacteria developed rapidly in shallow enclosures reaching levels only observed during bloom events in eutrophic lakes.
2. In the shallow enclosures, particulate phosphorus (PP) was on average 35% higher in comparison with deep enclosures, suggesting that depth plays a key role in P uptake by algae. Phytoplankton communities in both deep and shallow enclosures were dominated by three cyanobacteria species – Aphanizomenon flos-aquae , Anabaena flos-aquae and Microcystis aeruginosa – which accounted for up to 70% of total phytoplankton biomass. However, the absolute biomass of the three species was much higher in shallow enclosures, especially Aphanizomenon flos-aquae . The three cyanobacteria species responded in contrasting ways to nutrient manipulation because of their different physiology.
3. Standardised concentrations of the hepatotoxic microcystin-LR increased as a result of nutrient manipulations by a factor of four in the treated enclosures. Increased biomass of inedible and toxin producing cyanobacteria was associated with a decline in Daphnia pulicaria biomass caused by a reduction in the number of individuals with a body length of >1 mm. Zooplankton biomass did not decline at moderate cyanobacteria biomass, but when cyanobacteria reached high biomass large cladocerans were reduced.
4. Our results demonstrate that zooplankton communities can be negatively affected by cyanobacterial blooms and therefore the potential to use herbivory to reduce algal blooms in such eutrophic lakes appears limited.