Abiotic and biotic processes in lakes recovering from acidification: the relative roles of metal toxicity and fish predation as barriers to zooplankton re‐establishment

1. Recovery of acidified aquatic systems may be affected by both abiotic and biotic processes. However, the relative roles of these factors in regulating recovery may be difficult to determine. Lakes around the smelting complexes near Sudbury, Ontario, Canada, formerly affected by acidification and metal exploration, provide an excellent opportunity to examine the factors regulating the recovery of aquatic communities. 2. Substantial recovery of zooplankton communities has occurred in these lakes following declines in acidity and metal concentrations, although toxicity by residual metals still appears to limit survival for many species. Metal bioavailability, not simply total metal concentrations, was very important in determining effects on zooplankton and was associated with a decrease in the relative abundance of cyclopoids and Daphnia spp., resulting in communities dominated by Holopedium gibberum. 3. As chemical habitat quality has improved and fish, initially yellow perch and later piscivores (e.g. smallmouth bass, walleye), have invaded, biotic effects on the zooplankton are also becoming apparent. Simple fish assemblages dominated by perch appear to limit the survival of some zooplankton species, particularly Daphnia mendotae. 4. Both abiotic (residual metal contamination) and biotic (predation from planktivorous fish) processes have very important effects on zooplankton recovery. The re‐establishment of the zooplankton in lakes recovering from stress will require both improvements in habitat quality and the restoration of aquatic food webs.     

Long-term responses of zooplankton to invasion by a planktivorous fish in a subarctic watercourse

1. Introduced or invading predators may have strong impacts on prey populations of the recipient community mediated by direct and indirect interactions. The long-term progression of predation effects, covering the invasion and establishment phase of alien predators, however, has rarely been documented.
2. This paper documents the impact of an invasive, specialized planktivorous fish on its prey in a subarctic watercourse. Potential predation effects on the crustacean plankton, at the community, population and individual levels, were explored in a long-term study following the invasion by vendace ( Coregonus albula ).
3. Over the 12-year period, the density and species richness of zooplankton decreased, smaller species became more abundant and Daphnia longispina , one of the largest cladocerans, was eliminated from the zooplankton community.
4. Within the dominant cladocerans, including Daphnia spp., Bosmina longispina and Bosmina longirostris , the body size of ovigerous females and the size at first reproduction decreased after the arrival of the new predator. The clutch sizes of Daphnia spp. and B. longirostris also increased.
5. Increased predation pressure following the vendace invasion induced many effects on the crustacean zooplankton, and we document comprehensive and strong direct and indirect long-term impacts of an introduced non-native predator on the native prey community.     

Differing effects of suspended sediments on the performance of native and exotic Daphnia

1. Although large cladocerans are usually uncommon in large rivers, Daphnia lumholtzi (an exotic species in North America) is widespread and occasionally abundant. We collected zooplankton on the Illinois River (Illinois, U.S.A.) in 1995 and 1996 and found that the peak density of D. lumholtzi (25 L⁻¹) typically exceeded that of all native species combined. Maximum density occurred during warm periods (up to 27 °C) when concentrations of inorganic suspended sediments were high (>50 mg L⁻¹).
2. Using a life table experiment, we examined the effects of variation in suspended sediment (0 and 80 mg L⁻¹) and food (10⁴ and 10⁵ Ankistrodesmus cells mL⁻¹) on fitness of D. lumholtzi and the native Daphnia parvula. Daphnia lumholtzi had greater survivorship than D. parvula in most treatments and higher life-time fertility than D. parvula in all treatments. Both species achieved their fastest intrinsic rates of growth in treatments with high food, but their responses to suspended solids differed. The growth rate of D. lumholtzi in high food was slightly increased by higher turbidity, whereas that of D. parvula was depressed.
3. Results suggest that the ability of D. lumholtzi to tolerate suspended solids is an important factor contributing to its success in invading North American rivers.     

Zooplankton interactions in an enclosure experiment: insights from stable isotope analyses

1. Density gradients of cladocerans and copepods were generated in an enclosure experiment to compare the impact on the plankton of a filter feeder (Daphnia hyalina × galeata) with that of more selective feeders (calanoid and cyclopoid copepods). The experiment was conducted in situ over 25 days during spring in a mesotrophic lake, Schöhsee, Germany. 2. The plankton community was monitored regularly. Daphniids were able to graze on the phytoplankton present, which mainly consisted of small (<1000 μm³) species, whereas copepods did not show any impact on algae. 3. At the end of the experiment, Daphnia and remaining cyclopoid copepods were harvested and sorted manually, prior to analyses for stable isotopes of carbon and nitrogen. Daphniids from mesocosms stocked purely with differing densities of Daphnia showed little variability in stable isotope values, whereas those that thrived in enclosure bags together with copepods exhibited lower δ¹³C values. 4. The change in Daphniaδ¹³C indicates a change of food sources, modified by the presence of the copepods: the higher the mean abundance of copepods in the enclosures, the more ¹³C‐depleted the daphniids. Increasing abundance of high nucleic acid (HNA) bacteria in the copepod bags may account for the trend in Daphniaδ¹³C via increased grazing on the bacteria themselves, or via grazing on phytoplankton utilising isotopically light CO₂ from respiratory release. 5. Cyclopoid copepod stable isotope signatures were related to Daphnia and copepod abundances in copepod bags, suggesting that cyclopoids preyed on the available zooplankton.     

Reproducibility of short-term and reproduction toxicity experiments with Daphnia magna and comparison of the sensitivity of Daphnia magna with Daphnia pulex and Daphnia cucullata in short-term experiments

Short-term toxicity tests with Daphnia magna are reasonably reproducible. The sensitivity of Daphnia pulex, Daphnia cucullata and Daphnia magna proved to be about the same in short-term tests with 15 different chemical compounds.Reproduction toxicity experiments with Daphnia magna can easily be carried out within three weeks. At least duplicate experiments are necessary to arrive at an approximate no-effect level.     

Food and feeding of aquatic larvae of the midge chaoborus flavicans (meigen) (diptera : chaoboridae) in the laboratory

Laboratory observations on the feeding of fourth instar larvae of Chaoborus flavicans (Meigen) show that features relating to the prey, such as swimming behaviour, size and shape, play a major role in determining the kind of food eaten by the predator.In tests with two interacting limnetic cyclopoid copepods, Cyclops abyssorum out-competed Mesocyclops leuckarti when Chaoborus was absent but did not do so when Chaoborus was present.     

五氯酚对大型溞的急性亚慢性和慢性毒性

本文采用换水式试验研究了五氨酚溞（ＰＣＰ）对大型（Ｄａｐｈｎｉａｍａｇｎａ）的急性、亚慢性和慢性毒性,稀释水硬度为８０─１００ｍｇ／Ｌ（以ＣａＣＯ３计）。急性和慢性试验均使用小于一日龄的幼溞,试验温度为２５─２６℃,慢性试验进行了２０ｄ。用小于一日龄幼溞进行的亚慢性试验暴露了１９ｄ,而用四日龄幼溞的亚慢性试验则进行了１６ｄ,水温均保持在１９─２０℃。ＰＣＰ对大型溞的２４ｈ和４８ｈＥＣ５０分别是４８９和２４５μｇ／Ｌ。依据第１胎所产幼溞数求得的最低可观察效应浓度（ＬＯＥＣ）和无可观察效应浓度（ＮＯＥＣ）,在慢性试验中分别是１６０和８０μｇ／Ｌ,在１９ｄ亚慢性试验中分别为２００和１００μｇ／Ｌ,二者相近。试验结果表明,第１胎所产幼溞数是敏感的指标。     

Disturbance,competition and the maintenance of clonal diversity in Daphnia pulex

Laboratory microcosm experiments tested the intermediate disturbance hypothesis, which states that the highest level of diversity (e.g. species diversity) will be maintained at intermediate scales of disturbance. The effects of disturbance on the maintenance of clonal diversity and on competitive interactions among clones of the obligately parthenogenetic freshwater cladoceran, Daphnia pulex were examined. No significant effect of disturbance size (i.e. dilution volume) on clonal diversity was noted. However, frequency of disturbance had a pronounced effect on clonal diversity, with the highest clonal diversity maintained at low to intermediate disturbance frequencies. Competitive hierarchies among clones were often invariant within a given experiment. Generally, one or two clones dominated, with several less abundant clones persisting throughout an experiment. Results suggest that low to intermediate disturbances could be important in the maintenance of genetic variation in natural populations (i.e. through pre-emption of competitive exclusion between genotypes). This could have a direct bearing on the maintenance of both intra- and interspecific diversity.     

Toxicity tests with Daphnids: Its application in the management of water quality

The possible role of Daphnia species in toxicity tests is discussed. In screening tests, effluent monitoring tests and legal tests daphnids are recommended as useful test organisms. They also may help to establish concentration limits for chemical water pollution (water quality criteria). As biological indicator organisms their use is limited.     

Timing of predation by rainbow trout controls Daphnia demography and the trophic status of a Minnesota lake

1. Stocking of lakes with rainbow trout is a common practice that presents a potential conflict for lake managers who must balance the interests of anglers with those concerned that zooplanktivory by trout may trigger a trophic cascade and result in decreased water clarity. 2. This study examined how the timing of trout stocking (autumn versus spring) in a Minnesota (U.S.A.) lake affected (i) the population dynamics of their zooplankton food supply (Daphnia pulicaria), (ii) phytoplankton biomass and water clarity and (iii) trout survival. Sizes of both Daphnia and trout populations were estimated acoustically with high‐frequency (192 kHz) sonar. 3. Daphnia were nearly eliminated from the lake during winters after trout were stocked in autumn. In both of these years (1996 and 1997), the Daphnia population was small in the spring, and grew during the summer and into the autumn as the trout population diminished. 4. The lake was then stocked in spring for 2 years (1998 and 1999). This fisheries manipulation alleviated predation over the winter, but increased predation on D. pulicaria during the spring, summer and autumn. However, the high mortality caused by the spring‐stocked trout was offset by even higher rates of reproduction by the relatively large populations of fecund Daphnia that survived the winter in 1998 and 1999. 5. Grazing by these dense populations of Daphnia produced clear‐water phases during May and June that were inhibited in autumn stocking years. In addition, the large Daphnia populations present during the spring and early summer of 1998 and 1999 provided abundant forage for trout. 6. This fisheries manipulation achieved seemingly mutually exclusive management objectives: a robust planktivorous sport fishery, and clear water for other forms of recreation.     

Are the same Compounds in Microcystis responsible for Toxicity to Daphnia and Inhibition of its Filtering Rate?

Three strains of Microcystis when supplied to Daphnia in mixtures with Scenedesmus differed in their power to inhibit filtering rates. The axenic strain PCC 7806 had the strongest effect (93% inhibition with 50% Microcystis in the food). This strain was toxic to daphnids since Daphnia died faster under these conditions than without any food. Strain PCC 7806 also exhibited strong toxicity against mice (LD₅₀ 22 mg/kg). When the toxicity against Daphnia and mice was tested with cells of Microcystis PCC 7806 which has been subjected to various extraction procedures, the extraction of freeze-thawed cells with water slightly reduced the mouse toxicity, eliminated Daphnia toxicity and reduced the inhibition of the filtering rate. After treatment with a lipophilic solvent, the cells of PCC 7806 still showed low mouse toxicity, but no longer inhibition of the filtering rate and no toxicity to Daphnia. Thus, our data suggest that Daphnia toxicity and inhibition of the filtering rate are caused by different compounds, but we cannot rule out the possibility that the factors toxic to mice and inhibitory to the filtering rate are identical.     

Developing the gastropod Pomacea lineata (Spix, 1827) as a toxicity test organism

The authors describe a screening method to semi-quantitatively determine time independent LC 50s and ILC 50s. The protocol is based on the response of starved 4-day-old snails (Pomacea lineata). The neonates were exposed to paraquat and a textile mill effluent for 4–15 days without food. The ILC 50 and time-independent LC 50 for paraquat were, respectively, approximately 0.15 and 0.35 mg.l^-1. The respective lowest observed mortality concentration (LOMC) and no observed mortality concentration (NOMC) were 0.12 and 0.07 mg.l^-1. Snails are not generally used in toxicity testing, however this test organism appears to be worthy of further development. It should prove particularly useful in northeast Brazil where lack of chemical analytical equipment and taxonomic keys for faunal surveys places the emphasis for pollution monitoring on toxicity testing.     

上海滴水湖两种枝角类牧食对浮游植物群落影响的模拟研究

于2012年9月通过浮游动物添加实验,研究了大型溞(Daphnia magna)和隆腺溞(Daphnia carinata)对上海滴水湖浮游植物群落结构的影响.结果表明,实验组氨氮和可溶性活性磷浓度与空白组相比显著增加,大型溞组浮游植物密度较空白组降低了70.3％,隆腺溞组浮游植物密度较空白组降低了80.0％,叶绿素a浓度分别下降了80.4％和75.2％,叶绿素a与氨氮、可溶性活性磷呈显著相关性.浮游植物的群落结构较空白组也发生较大变化,硅藻、蓝藻和绿藻密度比例明显降低,隐藻、裸藻和甲藻在实验结束时没有检出,说明大型溞和隆线溞能有效控制水体中浮游植物密度,并能够对浮游植物群落结构产生影响.同时,附着藻类密度较空白组也有明显减少,说明大型溞和隆线溞对附着藻类也有一定的牧食作用.     

Variation in the species of freshwater harpacticoid copepods in Japan. II. Attheyella nakaii (Brehm)

Morphological variation in Attheyella nakaii, a dominant species of the genus in the mountain waters of Japan, is presented. The greatest proportion of male type furcal rami in the females of local populations is seen at the northern border of the range, where this species shows a sympatric distribution with A. yesoensis. Diminution of the inner lateral setae of endopodites on legs 2–4 occur in Kyushu and the Ryukyu Islands. The body size and relative length of the leg 5 exopodite show a latitudinal cline. The population of the type locality of this species exhibits a truncated form of furcal rami.