Impact of turbulence on riverine zooplankton: a mesocosm experiment

1. With increases in river discharge over time and space, zooplankton generally encounter increased turbulence, turbidity, hydraulic forces, downstream advection and food limitations, all of which should affect species diversity and densities. Of these factors, the role of turbulence on the distribution of zooplankton is least known along longitudinal and lateral dimensions in river networks. 2. We tested the factorial effects of turbulence and grazing level on Ohio River potamoplankton in spring and summer using twelve 1600‐L, outdoor mesocosms. Turbulence was calculated using the Froude number for equal depths but with current velocities of 0.064 and 0.32 m s^?1. Grazing levels corresponded to a high density treatment (=ambient river densities of rotifers, copepods and cladocerans) and a low density treatment (initially no zooplankton >64 μm). All tanks had the same water residence time, and hydraulic stress was minimized by circular flow patterns. 3. Zooplankton densities and population growth rates were significantly affected by turbulence level and season. In general, rotifer populations grew faster in high turbulence tanks (though Keratella and Brachionus populations flourished in both treatments in summer) and microcrustaceans thrived better in low turbulence environments. The larger, calanoid copepods handled more turbulent conditions much better than cyclopoids or nauplii. Zooplankton had no detectable effects on particulate organic carbon concentrations in either month (values were higher in spring), but rotifers reduced chlorophyll concentrations in both months. 4. The relative importance of turbulence in controlling potamoplankton is probably to vary not only on a longitudinal basis in river networks but also with both the hydrogeomorphic complexity of river reaches and the type and amount of river regulation. Plans for river rehabilitation and management should incorporate non‐turbulent habitats in large rivers as a means of enhancing zooplankton populations and providing an important food web component for planktivores.     

Assessing the health of a zooplankton community in a small Precambrian Shield lake during recovery from experimental acidification

Acidified lakes recover chemically relatively quickly following the reduction or cessation of acidic inputs. Although fish, invertebrate, and phytoplankton communities are reported to begin to return to preacidification states in chemically-improving lakes, the process and extent of biological recovery are not well-documented. The experimental acidification of Precambrian Shield Lake 223 (27.4 ha surface area; 14.4 m maximum depth) in the Experimental Lakes Area in northwestern Ontario, provides an opportunity to compare the zooplankton community prior to acidification with that during progressive acidification and during chemical recovery. Acidified with sulfuric acid from pH 6.47 (ice-free season mean) in 1976 to pH 5.0 (1981 to 1983), Lake 223 has been allowed to recover in steps of pH 5.5 (1984 to 1987), pH 5.8 (1988 to 1990), and pH 6.11 (1991). Total zooplankton biomass showed no trend to increase or decrease during the acidification and recovery, but species composition changed. Compared with species composition at pH 6.13 early in acidification in 1977, the recovering community at pH 6.11 in 1991 had the previously-dominant cladoceran species present in very low numbers and had two newly-appearing cladoceran species. The community had lost one species of calanoid and gained none and lost two species of cyclopoids and gained two. It appeared to lose four species of rotifiers and gain seven. In nearby unmanipulated reference Lake 239 (56.1 ha; 30.4 m), species shifts were recorded but they involved rarer species, not dominants as in Lake 223. Although the zooplankton community in 1991 is in a new state with respect to species composition, static measures of total community biomass, contribution to biomass by the four main taxonomic groups, per cent smilarity to the preacidification community (for crustaceans), and biomass of herbivores do not indicate impairment of community health. Lowered species diversity for both crustaceans and rotifers partially returned to preacidification levels. Nevertheless, the rotifer community in 1991 was more dissimilar to the preacidification community than was the crustacean community, and carnivore biomass appeared to be depressed in Lake 223. The Lake 223 zooplankton community at pH 6.11 in 1991 appears to be in a state of flux.     

Effects of thermal effluents from the Bergum Power Station on the zooplankton in the Bergumermeer

The influence of thermal discharge from a 640 MW steam electric power station on the Bergumermeer (shallow, eutrophic lake) was investigated. The temperature of the thermal effluent did not exceed 30 °C. The lake was sampled extensively from 1975 to 1978. Zooplankton densities at different depths in the heated and non-heated parts of the lake were compared. A vital staining technique was used to assess entrainment mortality of cladocerans. The entrainment mortalities for the most abundant cladocerans were only 2 to 3% but for Leptodora kindtii 19% and about 25% for Diaphanosoma brachyurum, Ceriodaphnia pulchella and the cyclopoid nauplii. The ecological consequences for the lake ecosystem are discussed.     

Daytime grazing and assimilation rates of planktonic copepods Acanthodiaptomus denticornis and Cyclops vicinus vicinus. Comparison of spatial and resource utilisation by rotifers and cladoceran communities in a eutrophic lake

The clearance rates of ¹⁴ carbon-labelled Chlamydomonas sp. by the copepodite and adult stages of the 2 dominant species of Copepoda were studied in eutrophic Lake Aydat. They varied from 30 to 3,007 µl ind^–1 h^–1 for Acanthodiaptomus denticornis (mean = 600 µl ind^–1 h^–1) and from 20 to 1,133 µl ind^–1 h^–1 for Cyclops vicinus (mean = 340 µl ind^–1 h^–1). Their maximum assimilation efficiencies were 58% and 50%, respectively. These populations collectively could consume the available food in 4 days during September (maximum daily grazing rate = 24%). Mean individual clearance rates could be ranked Acanthodiaptomus denticornis > Ceriodaphnia quadrangula > Chydorus sphaericus > Daphnia longispina > Cyclops vicinus vicinus > Bosmina longirostris > K. cochlearis > K. quadrata and Kellicottia longispina. Like cladocerans and rotifers, the copepods living in this eutrophic lake can feed at low oxygen concentrations.     

Zooplankton biomass dynamics in oligotrophic versus eutrophic conditions: a test of the PEG model

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Projected impacts of 21st century climate change on diapause in Calanus finmarchicus

Diapause plays a key role in the life cycle of high latitude zooplankton. During diapause, animals avoid starving in winter by living in deep waters where metabolism is lower and met by lipid reserves. Global warming is therefore expected to shorten the maximum potential diapause duration by increasing metabolic rates and by reducing body size and lipid reserves. This will alter the phenology of zooplankton, impact higher trophic levels and disrupt biological carbon pumps. Here, we project the impacts of climate change on the key North Atlantic copepod Calanus finmarchicus under IPCC RCP 8.5. Potential diapause duration is modelled in relation to body size and overwintering temperature. The projections show pronounced geographic variations. Potential diapause duration reduces by more than 30% in the Western Atlantic, whereas in the key overwintering centre of the Norwegian Sea it changes only marginally. Surface temperature rises, which reduce body size and lipid reserves, will have a similar impact to deep‐water changes on diapause in many regions. Because deep‐water warming lags that at the surface, animals in the Labrador Sea could offset warming impacts by diapausing in deeper waters. However, the ability to control diapause depth may be limited.     

The recovery of crustacean zooplankton from acidification depends on lake type

Acidification has harmed freshwater ecosystems in Northern Europe since the early 1900s. Stricter regulations aimed at decreasing acidic emissions have improved surface-water chemistry since the late 1980s but the recovery of biotic communities has not been consistent. Generally, the recovery of flora and fauna has been documented only for a few lakes or regions and large-scale assessments of long-term dynamics of biotic communities due to improved water quality are still lacking. This study investigates a large biomonitoring dataset of pelagic and littoral crustacean zooplankton (Cladocera and Copepoda) from 142 acid-sensitive lakes in Norway spanning 24 years (1997–2020). The aims were to assess the changes in zooplankton communities through time, compare patterns of changes across lake types (defined based on calcium and humic content), and identify correlations between abiotic and biological variables. Our results indicate chemical and biological recovery after acidification, as shown by a general increase in pH, acid neutralizing capacity, changes in community composition and increases in the total number of species, number of acid-sensitive species and functional richness through time. However, the zooplankton responses differ across lake types. This indicates that the concentration of calcium (or alkalinity) and total organic carbon (or humic substances) are important factors for the recovery. Therefore, assessment methods and management tools should be adapted to the diverse lake types. Long-term monitoring of freshwater ecosystems is needed to fully comprehend the recovery dynamics of biotic communities from acidification.     

Cost of reproduction in selected species of zooplankton (rotifers and cladocerans)

Reproduction is an energetically costly biological process. Among the freshwater zooplankton, rotifers and cladocerans reproduce parthenogenetically and the cost of reproduction can be estimated using the life table data from demographic studies. Reduced probability of future survival or future reproduction as a result of current investment in offspring production (trade-off) is the central theme of the cost hypothesis. Correlations using present reproduction vs. future reproduction (called the reproductive costs) or future survival (called the survival costs) can be used to evaluate the cost hypothesis. In this work sets of correlations were made: (1) between present reproduction (m _x) vs. future survival (l _x+1, l _x+2, l _x+3 etc. for the entire lifespan) (survival costs), and (2) present reproduction (m _x) vs. future reproduction (m _x+1, m _x+2, m _x+3 etc. for the entire reproductive span) (reproductive costs). These correlations were plotted against the cohort age-classes in order to quantify survival and reproductive costs in rotifers (Asplanchna girodi, Brachionus macracanthus, B. variabilis and Platyias quadricornis) and cladocerans (Ceriodaphnia cornuta – one strain maintained on Chlorella and another strain adapted to Microcystis), Daphnia carinata, D. laevis, Moina macrocopa, Pleuroxus aduncus, Scapholeberis kingi and Simocephalus vetulus). All the tested rotifer species showed negative tendency in correlation coefficients (when the data of current reproduction vs. future reproduction and future survival were plotted) for both reproductive and survival costs. However, from the total survival and reproductive costs derived, 84% of the former and 42% of the latter were statistically significant. In cladocerans about 80% of the costs (correlations between current reproduction vs. future survival or future reproduction) were negative suggesting that present reproduction had negatively affected both the further survival and reproduction of test populations. In terms of statistically significant survival costs, the cladocerans showed a trend slightly lower (72%) but comparable to rotifers. The reproductive costs were significant in 45% cases. In our study, the simple statistical correlations detected the trade-offs between reproduction and survival. Thus, in more than 60% cases of both survival and reproductive costs in zooplankton were negative, and our data supported the cost hypothesis, in the majority of cases where reproduction by zooplankton of a given age class caused reduced survival and reproduction of the next age class.     

Effect of temperature on the termination of diapause in the univoltine almond seed wasp Eurytoma amygdali

Diapausing larvae of Eurytoma amygdali Enderlein (Hymenoptera, Eurytomidae) were collected in early August and late September. They were subjected to various photoperiod and temperature regimens for up to 20 weeks, then kept at L16:D8 and 19 °C for another 14 to 26 weeks for diapause to be terminated and pupation to take place. Photoperiod did not affect diapause completion. It was confirmed that the two morphologically distinct diapause stages have different temperature requirements for their completion. The first diapause stage was completed synchronously at temperatures between 16 and 19 °C. A higher temperature of 26 °C delayed diapause development. The second stage required lower temperatures between 4 and 10 °C. Spontaneous termination of diapause was observed at constant 19 °C. When applied to the first diapause stage for 20 weeks, low temperatures made the larvae refractory to subsequent intermediate temperatures. The first stage was thus maintained until a higher temperature of 26 °C made the larvae regain their ability to respond to the intermediate temperatures and complete this stage. Larvae grown in Retsou almonds had a higher diapause intensity than larvae grown in Truoito almonds. The results suggest that, in nature, the high temperatures of late summer and early autumn are likely to maintain the first diapause stage. Subsequently, the less warm temperatures of autumn allow the completion of the first stage by late autumn, and the low temperatures of late autumn and of winter allow the completion of the second diapause stage by mid winter.     

The effect of larval photoperiod on pupal colour and diapause in swallowtail butterflies

ABSTRACT.

• 1 There are significant differences in the effects of larval photo-period on diapause and pupal colour among the species Papilio polyxenes Fabr., P.troilus L., Battus philenor (L.) and Eurytides marcellus (Cramer).
• 2 Diapause and pupal colour in P.polyxenes and P.troilus are strongly influenced by larval photoperiod, short photophase eliciting brown diapausing pupae. Photoperiods of 15L:9D permit the expression of the green and brown pupal colour alternatives.
• 3 Pupal colour in B.philenor and E.marcellus is not affected by larval photoperiod, but short photophase induces diapause in these species.
• 4 All species except B.philenor show an association between brown pupal colour and diapause: Emarcellus when reared on long (midsummer) photophase, P.polyxenes and P.troilus when reared on short (autumnal) photophase.
• 5 In P.polyxenes, short photophase can affect pupal colour responses directly, whether the individual enters diapause or not.
• 6 Differences among the species are related to differences in the ecology of their natural pupation sites.

     

The effect of Cyanophyta upon zooplankton in a eutrophic tropical lake (Lake Valencia,Venezuela)

The effect which Cyanophyta have upon the zooplankton varies according to the form of the alga (mucilaginous colonies or filaments) and its abundance. Periodical blooms of Microcystis aeruginosa were not detrimental for the zooplankton, in spite of the fact that copepods, cladocerans and rotifers consume small colonies. High concentrations of Lyngbya limnetica and Oscillatoria limnetica in Lake Valencia, Venezuela, proved to be inhibitory for cladocerans. A total absence of cladocerans was detected when filaments increased.     

Long-term droughts change the hatching patterns of zooplankton resting eggs from permanent and temporary lakes

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桡足类滞育规律研究

首次提出用滞育指数对桡足类滞育能力进行相对量化处理 ,并对 10 2种桡足类的滞育能力同迁移能力、体长、栖息地之间的关系进行了数学分析 ,初步得出了滞育在桡足类中的分布规律 :在桡足类中滞育与迁移呈负相关 ,两者之间存在一定程度的置换 ;个体较小的桡足类一般具有较强的滞育能力和较弱的迁移能力 ,个体较大的桡足类一般具有较弱的滞育能力和较强的迁移能力 ;淡水桡足类一般比海洋桡足类具有较强的滞育能力。最后探讨了这种分布模式的成因     

Variation in torpidity of diapause in freshwater cyclopoid copepods

By successively filtering off animals emerging from mud cores taken to the laboratory, the degree of torpidity within the same species was found to vary considerably both time and space. Variation in time from the start of dormancy follows a pattern of diapause development similar to that of insect diapause. In some localities dormancy is deep and prolonged, while in others it is less pronounced and lasts for a shorter period. The depth of torpidity during winter seems to be correlated to an induction early in the year. The intensity of diapause varies along the slope of the localities and down into the bottom mud. In some cases high temperatures seem to induce a deeper torpidity.     

滞育烟蚜茧蜂的亲代效应评价

【目的】烟蚜茧蜂Aphidius gifuensis Ashmead是可持续防控蚜虫的优良内寄生蜂,适宜的低温短光照可诱导其进入滞育,滞育后产品货架期长达120 d,对害虫生防意义重大。为深入探索滞育烟蚜茧蜂的亲代效应,分析滞育机理,提高滞育诱导效率,指导该天敌产品的贮存实践,开展本项研究。【方法】在室内测试了滞育烟蚜茧蜂F1代的羽化率、性比、成蜂寿命、滞育率、寄生力以及F2代的羽化率、性比等生物学指标,综合评价滞育烟蚜茧蜂的亲代效应。【结果】滞育经历对烟蚜茧蜂子代的部分生物学性状具有显著性影响,F1代雌蜂比例显著增加,滞育维持30 d后子代雌蜂比例由0.59上升至0.65;F2代雌蜂比例与CK无差别,维持在0.58左右;F1代滞育率显著升高,可由对照的44.75%提高至74.01%,滞育维持30 d后子代滞育率具升高趋势;F1代寄生力略增加,各处理形成的僵蚜数在117~129头间,但无显著性差异;F1代羽化率、子代成蜂寿命与CK相比无差异。【结论】烟蚜茧蜂具有较显著的滞育亲代效应,亲代滞育经历可显著提高子一代的滞育率,利于子代抵御不良环境胁迫,提高种群存活率。     

Feeding patterns of dominant Antarctic copepods: an interplay of diapause,selectivity, and availability of food

Gut contents and feeding activity of five dominant Antarctic copepods (Calanus propinquus, Calanoides acutus, Rhincalanus gigas, Metridia gerlachei and Microcalanus pygmaeus) were studied from samples collected during several cruises of the RV Polarstern to the eastern Weddell Sea. In summer, feeding activity, estimated as percentage of copepods with food in the guts, was high in all the species, and diatoms dominated all gut contents. In winter, C. acutus was trophically inactive, and C. propinquus and R. gigas considerably decreased their feeding activity, while a decrease in feeding of M. gerlachei and M. pygmaeus was less pronounced. Unidentified mass dominated gut contents in winter, supplemented by phytoplankton and protozoans. Prior to the spring bloom, feeding activity of C. acutus was low, with unidentified food predominating, while carnivory was important in actively feeding C. propinquus. Rhincalanus gigas tended to be more carnivorous than C. acutus, however with less feeding activity than C. propinquus. Seasonal changes in feeding patterns are discussed.     

松毛虫赤眼蜂滞育诱导及解除条件研究

【目的】以柞蚕Antheraea pernyi卵为繁殖寄主,对松毛虫赤眼蜂Trichogramma dendrolim滞育诱导及解除条件进行研究,以解决赤眼蜂工厂化生产和大面积应用中面临的的中、长期储存问题。【方法】通过观测不同发育阶段(寄生柞蚕卵在26℃培养40、96和144 h)、滞育诱导温度(10、13和16℃)和诱导时间对松毛虫赤眼蜂滞育的影响,确定松毛虫赤眼蜂滞育诱导条件;通过观测滞育诱导温度和滞育后的贮藏温度对滞育解除的影响,确定松毛虫赤眼蜂滞育解除条件。【结果】在松毛虫赤眼蜂的不同发育阶段对其进行持续的低温刺激均能使其导入滞育,但以小幼阶段(26℃培养40 h)开始效果最佳,寄生卵在26℃培养40 h后,转入10℃和13℃下连续诱导31 d,滞育率可达100%和99.12%。滞育诱导温度和滞育后的贮藏温度对松毛虫赤眼蜂解除滞育所需时间和解除滞育后的羽化出蜂率有较大影响,10℃诱导滞育后置于1℃冷藏的赤眼蜂解除滞育所需时间最短,解除滞育后的羽化出蜂率和单卵出蜂数更高,更耐储存。此条件下冷藏约30 d开始打破滞育,在正常发育下温度下羽化出蜂,60 d羽化出蜂率达到95.24%,冷藏4个月后羽化出蜂率仍在60%以上,单卵出蜂数高于50头。【结论】松毛虫赤眼蜂最佳滞育诱导条件为26℃培养40 h后,转入10℃连续低温诱导31 d;最佳滞育解除条件为1℃低温储存,但储存期不能超过4个月。     

Feeding insects with a phytopathogenic fungus influences their diapause and population dynamics

Abstract.  1. A facultative mutualistic relationship between a herbivorous moth, Lobesia botrana , and a phytopathogenic fungus, Botrytis cinerea , both damaging the same plant, the vine, has been demonstrated recently. Laboratory and field studies were carried out to determine the influence of the presence of the fungus in food on larvae during the pre- and post-diapause periods and on the global fitness of the insect.
2. During the pre-diapause period, larvae fed on fungus exhibited a higher survival rate and a faster larval development than insects reared without fungus.
3. After the wintering diapause, insects reared with fungus displayed a better synchronisation of adult emergence and an increased fecundity compared with control insects.
4. These results indicate that food containing fungus provides an improved diet, permitting the herbivorous insect to obtain nutrients required to optimise their life-history traits.
5. In addition, the results emphasise the importance of the nutritional quality of larval diet, improved by addition of the fungus, on diapause termination and on the demography of the insect before and after the wintering diapause.