Feeding behaviour of major 0 + fish species in a shallow, eutrophic lake (Tjeukemeer, The Netherlands)

The forage base and the food selectivity of 0+ representatives of six abundant freshwater fish species were studied in a shallow, eutrophic Dutch lake. Most species relied on the zooplankton; the size-selective predation in early summer was directed to the smaller copepods and in late summer to larger cladocerans and copepods than concurrently present in the lake. Daphnia spp. and cyclopoid copepods were the main zooplankton taxa for smelt, perch and pikeperch. Energetically, the large cladoceran, Leptodora kindtii, was especially important for pikeperch. Bream and roach preyed upon smaller zooplankton than the other fish species. The influence of the zooplankton predation by abundant 0+ fish was clear from a small mean Daphnia size in September; this size is to be used as an indicator in fishery management. Neomysis integer, the most important macrofauna species, was consumed by perch, pikeperch and ruffe; pikeperch was most size-selective in this respect. The 0+ ruffe was à typically benthivorous fish. Only the 0+ pikeperch became piscivorous, especially in years when smelt was abundant.     

Food and food selection of cisco (Coregonus albula L.) in a dysoligotrophic lake

With minor exceptions, cisco (C. albula) in Lake Suomunjärvi fed on cladocerans and copepods. The food habits were different among two size classes of fish. The composition of cisco diet changed at different depths and times of the day, but the distribution of zooplankton was usually very similar in each period irrespective of the depth or diel period. Daphnia, Bosmina, Cyclops scutifer and Heterocope appendiculata were the main diet of cisco. Calculations of fish electivity indices showed that cisco selected usually large species of cladocerans and copepods and a small cladoceran, Bosmina coregoni. Body-size selection was clear for Daphnia and Bosmina.     

Responses of cyanobacteria to herbivorous zooplankton across predator regimes: who mows the bloom?

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Zooplankton dynamics in a gypsum karst lake and interrelation with the abiotic environment

Zooplankton species composition and abundance variation was studied in Lake Amvrakia, which is a deep, temperate, gypsum karst lake situated in the western Greece. The two year survey of zooplankton revealed 33 species (23 rotifers, five cladocerans, four copepods and one mollusc larva). The mean integrated abundance of the total zooplankton ranged between 83.6 and 442.7 ind. L⁻¹, with the higher density to be recorded in the surface 0–20 m layer. Small numbers of specimens of almost all species were found also in the hypoxic or anoxic hypolimnion. Copepods and especially the calanoid Eudiaptomus drieschi dominated the zooplankton community throughout the sampling period, followed by Dreissena polymorpha larvae, rotifers and cladocerans. Seasonal succession among the cladocerans and the most abundant rotifer species was observed. The concentration of chlorophyll-a was the most important factor for the variation of total zooplankton, as well as for the rotifers’ community. Dissolved oxygen affected copepods and cladocerans, water level correlated mainly with the molluscs larvae of D. polymorpha, while temperature influenced the variation of several rotifers, the cladoceran Diaphanosoma orghidani and the mollusc larvae. Negative correlation of conductivity with the cladoceran Daphnia cucullata and the copepods E. drieschi and Macrocyclops albidus was found. The differences in species composition found in Lake Amvrakia in comparison to the nearby lakes are probably ought to the geographical isolation and perhaps to its particular chemistry (e.g., elevated conductivity).     

A comparison of the trophic transfer of fatty acids in freshwater plankton by cladocerans and calanoid copepods

1. Analyses of zooplankton fatty acid (FA) composition in laboratory experiments and samples collected from lakes in New Zealand spanning a wide gradient of productivity were used to assess the extent to which FAs might infer their diet. We used the cladocerans, Daphnia and Ceriodaphnia, and the calanoid copepod, Boeckella, as test organisms, and monocultures of cryptophytes, chlorophytes and cyanobacteria as food. Based on reproductive success, cryptophytes were the highest food quality, chlorophytes were intermediate and cyanobacteria the poorest. 2. Several FA groups were highly correlated between zooplankton and their diets. They were monounsaturated fatty acids (MUFAs), and ω3 and ω6 polyunsaturated fatty acids (PUFAs) for cladocerans, and saturated fatty acids (SAFAs) and ω3 PUFAs for copepods. Several FAs varied significantly less in the zooplankton than in their monoculture diets, e.g. MUFAs in Daphnia, and ω3 and ω6 PUFAs in Ceriodaphnia, despite clear dietary dependency for these FAs. 3. Zooplankton collected from lakes in New Zealand had more eicosapentaenoic acid (EPA) (Daphnia), more highly unsaturated ω3 and ω6 FAs (C₂₀, C₂₂; Daphnia, Ceriodaphnia, Boeckella) and less ω3 C₁₈ PUFAs (Daphnia, Ceriodaphnia, Boeckella) and ω6 C₁₈ PUFAs (Daphnia, Ceriodaphnia) than measured in the same species reared on phytoplankton in the laboratory. 4. Analyses of FA composition of seston and freshwater zooplankton globally showed that, in general, zooplankton had a significantly higher proportion of arachidonic acid and EPA than seston, and copepods also had a higher percentage of docosahexaenoic acid than seston. 5. These results suggest that zooplankton selectively incorporate the most physiologically important FAs. This could be a consequence of preferential assimilation, selective feeding on more nutritious cells or locating and feeding within higher food quality food patches.     

Zooplankton community structure driven by vertebrate and invertebrate predators

Summary A zooplankton community was established in outdoor experimental ponds, into which a vertebrate predator (topmouth gudgeon: Pseudorasbora parva) and/or an invertebrate predator (phantom midge larva: Chaoborus flavicans) were introduced and their predation effects on the zooplankton community structure were evaluated. In the ponds which had Chaoborus but not fish, small- and medium-sized cladocerans and calanoid copepods were eliminated while rotifers became abundant. A large-sized cladoceran Daphnia longispina, whose juveniles had high helmets and long tailspines as anti-predator devices, escaped from Chaoborus predation and increased. In the ponds which had fish but not Chaoborus, the large-sized Daphnia was selectively predated by the fish while small-and medium-sized cladocerans and calanoid copepods predominated. In the ponds containing both Chaoborus and fish, the fish reduced the late instar larvae (III and IV) of Chaoborus but increased the early instar larvae (I and II). Small- and large-sized cladocerans were scarcely found. The former might have been eliminated by predation of the early instar larvae of Chaoborus, while the latter was probably predated by fish. Consequently, the medium-sized cladocerans, which may have succeeded in escaping from both types of predator, appeared abundantly. The results suggest that various combinations of vertebrate and invertebrate predators are able to drive various kinds of zooplankton community structure.     

Studies on functional response and prey selection using zooplankton in the anostracan Chirocephalus diaphanus Prevost, 1803

Freshwater cladocerans and rotifers were used as prey to study functional response and prey selection by adult females of Chirocephalus diaphanus under laboratory conditions. For functional response studies, we offered three rotifer species (Brachionus calyciflorus, B. patulus and Euchlanis dilatata) and three cladoceran species (Alona rectangula, Ceriodaphnia dubia and Moina macrocopa) at various densities ranging from 0.5 to 16 ind. ml^–1. We found increased zooplankton consumption with increasing prey density but beyond 4 ind ml^–1 cladocerans and 8 ind. ml^–1 rotifers, the number of animals eaten plateaued. In general, C. diaphanus consumed fewer large prey (cladocerans) and many more smaller zooplankton (rotifers). For prey selection experiments, we used B. calyciflrous, B. patulus, C. dubia and M. macrocopa, offered at the ratio of two rotifers: one cladoceran and at three prey densities (total zooplankton numbers: 3, 6 and 12 ind. ml^–1). Prey selectivity patterns followed the functional response trends. In general, regardless of prey types, with an increase in the available zooplankton, there was an increase in the number of prey consumed. At any given prey density, C. diaphanus consumed higher numbers of rotifers than cladocerans. Among the prey offered, B. patulus and M. macrocopa were positively selected. Results are discussed in light of possible control of zooplankton by anostracans in temporary ponds.     

Competition between rotifers and cladocerans of different body sizes

Summary We conducted laboratory experiments to test the hypothesis that rotifers could coexist with small (<1.2 mm) but not large (>1.2 mm) cladocerans. Keratella cochlearis was excluded in <8 days by the large cladocerans Daphnia pulex and D. magna, probably through both interference and exploitative competition. On the other hand, K. cochlearis persisted for 8 weeks with two small cladocerans (Bosmina longirostris and Ceriodaphnia dubia) and excluded a third small cladoceran (D. ambigua). Similarly, Synchaeta oblonga coexisted with B. longirostris for >7 weeks, and K. testudo coexisted with D. ambigua for >4 weeks. Coexistence of small cladocerans and rotifers was always accompanied by suppression of one or both populations, probably primarily if not exclusively by exploitative competition for limiting food resources. These results indicate that the competitive dominance of cladocerans over rotifers decreases markedly with cladoceran body size and that factors other than body size may determine the competitive outcome between rotifers and small cladocerans. Our study provides a mechanistic explanation for a commonly observed pattern in natural zooplankton communities: planktonic rotifers often are abundant when only small cladocerans occur but typically are rare when large cladocerans are present.     

Effect of mixed diets (cyanobacteria and green algae) on the population growth of the cladocerans <Emphasis Type="Italic">Ceriodaphnia dubia</Emphasis> and <Emphasis Type="Italic">Moina macrocopa</Emphasis>

Microcystis aeruginosa, a cosmopolitan form, is a colonial cyanobacterium, which is also common in many freshwater bodies in Mexico. In eutrophic water bodies cyanobacteria are often the main phytoplankton that co-exist with cladocerans. We evaluated the effect of mixed diets, comprising 0, 25, 50, 75, and 100% on dry weight basis of M. aeruginosa, and the rest of one of two green algal species (Chlorella vulgaris and Scenedesmus acutus), on the population growth of the cladocerans Ceriodaphnia dubia and Moina macrocopa. Regardless of the share of M. aeruginosa in the mixed diet, C. dubia fed Chlorella had a longer initial lag phase. However, in mixed diet with S. acutus, the lag phase of C. dubia increased with increasing proportion of M. aeruginosa. When raised on 100% M. aeruginosa, the population growth of C. dubia was lowered compared with 100% S. acutus or 100% C. vulgaris. Increased proportion of M. aeruginosa in the mixed diet also resulted in decreased abundance of M. macrocopa. Irrespective of diet type, M. macrocopa had a shorter lag phase than C. dubia. Depending on the diet type, the rate of population increase (r) of C. dubia varied from 0.07 to 0.26 d⁻¹ while that of M. macrocopa was higher (0.14–0.61 d⁻¹). For both cladoceran species, the lower r values were obtained when fed Microcystis. Our study showed that the strain of M. aeruginosa was not highly toxic to cause total elimination of either C. dubia or M. macrocopa. Addition of a green algal component to the diet improved the population growth rates of both cladoceran species.     

The food preference of vendace (Coregonus albula) in South Swedish forest lakes including the predation effect on zooplankton populations

Vendace (Coregonus albula, L.) is in the southern part of its distribution area during the summer period restricted to hypolimnion. Food is dominated by Bosmina coregoni and Daphnia sp. The selectivity index is highest for large cladocerans and large copepods.The pelagic crustacean fauna in vendace lakes is dominated by small species like Bosmina coregoni, Daphnia cristata, Thermocyclops and Mesocyclops sp. and Eudiaptomus sp. During periods of maximum vendace abundance only Bosmina coregoni is left of the cladocerans, while the abundance of cyclopoid copepods increases.     

Effects of toxic and non-toxic cyanobacteria on the life history of tropical and temperate cladocerans

1. This study compares the effects of four toxic strains of Microcystis aeruginosa on tropical and temperate Cladocera. Survival was tested in acute toxicity experiments using Microcystis alone or in mixtures with the edible green algae Ankistrodesmus falcatus. The effect of chronic exposure on population growth was estimated in life‐table experiments by varying the proportion of Microcystis and the green alga. Nutritional deficiency was assessed using a non‐toxic cyanobacterium in a zooplankton growth experiment. Feeding inhibition was tested using a C‐labelled green alga as a tracer in mixtures with toxic Microcystis.
2. Toxicity varied consistently between Microcystis strains, while sensitivity varied consistently between cladoceran species. However, no relationship was found between sensitivity and geographical origin or cladoceran body size. Two small‐bodied cladocerans from the same tropical lake, Ceriodaphnia cornuta and Moinodaphnia macleayi, were the least sensitive and most sensitive species, respectively.
3. Surprisingly, two small tropical cladocerans survived longer without food than did three large Daphnia species and a third small tropical species.
4. Each of the three tropical Microcystis strains strongly reduced the population growth rate (little ‘r’) and reproductive output of each cladoceran, this reduction being proportional to the percentage of toxic cells in the diet.
5. As the sole food source, the non‐toxic cyanobacterium, Synechococcus elongatus, supported poor growth in M. macleayi. The nutritional deficiency was overcome when Synechococcus was mixed with either Ankistrodesmus or an emulsion rich in omega‐3 fatty acids.
6. Microcystis inhibited the feeding rate of two cladocerans, even when it comprised only 5% of a mixture with the green algae A. falcatus.
7. Differences in sensitivity to the toxic cyanobacterium appear to be associated with differences in life history between the cladoceran species rather than differences between tropical and temperate taxa. Slow‐growing species that are resistant to starvation appear less sensitive to toxic Microcystis than fast‐growing species, which also tend to die more quickly in the absence of food.     

Effects of the blue-green alga Microcystis aeruginosa on zooplankton competitive relations

Summary Field distribution patterns and laboratory feeding experiments have suggested that blooms of colonial blue-green algae strongly inhibit relatively large-bodied daphnid cladocerans. We conducted laboratory experiments to test the hypothesis that blooms of the colonial blue-green alga Microcystis aeruginosa would shift competitive dominance away from large-bodied daphnid cladocerans toward smaller-bodied cladocerans, copepods, and rotifers. In laboratory competition experiments, increasing the proportion of M. aeruginosa in the algal food supply resulted in a shift from dominance by the relatively largebodied cladoceran Daphnia ambigua to dominace by the copepod Diaptomus reighardi. The small-bodied cladoceran Bosmina longirostris was always numerically heavily dominant over D. ambigua, but its estimated population biomasses were only slightly higher than those of D. ambigua. Daphnia ambigua consistently outcompeted the rotifer Brachionus calyciflorus. Our results demonstrate that blooms of M. aeruginosa can alter zooplankton competitive relations in laboratory experiments, favoring small-bodied cladocerans and copepods at the expense of large-bodied cladocerans. However, contrary to predictions, blooms of M. aeruginosa did not improve the competitive ability of rotifers.     

The late summer crustacean zooplankton in western U.S.A reservoirs reflects ecoregion,temperature and latitude

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Zooplankton dynamics in the upstream part of Stratos reservoir (Greece)

The investigation of the zooplankton community in the upstream part of Stratos reservoir during a 24 months survey (September 2004–August 2006) revealed 26 invertebrate species (14 rotifers, 6 cladocerans, 5 copepods and one mollusk larva). The mean abundance of the total zooplankton was higher in the first sampling period (2004–2005) and ranged between 8.81 and 47.74 ind. L⁻¹, than the second period (2005–2006) when fluctuated between 1.91 and 43.09 ind. L⁻¹. The seasonal variation was strongly influenced by the presence of rotifers, which accounting on average for 68.4% in total. Among them Keratella cochlearis and the order Bdelloidea were numerically the most important, while Macrocyclops albidus prevailed among the copepods and Bosmina longirostris among the cladocerans. Dreissena polymorpha was the only mollusk found in the zooplankton community. Rotifers, copepods and cladocerans showed a seasonal succession with the former preceding in the abundance having their first maximum in spring, while copepods and cladocerans followed, having peaks of abundance in early summer and in autumn, respectively. No seasonal succession among the cladoceran species was observed. The intense water flow in the upstream part of the reservoir, as well as temperature, conductivity, DO, pH, phosphates and silicates, were significant parameters controlling abiotic and biotic elements of the ecosystem and consequently influencing the seasonal variation and the dynamics of the zooplankton community.     

Selective predation on zooplankton by pelagic Arctic charr, Salvelinus alpinus, in six subarctic lakes

Selective predation by planktivore fish appears to be an important regulatory factor of zooplankton communities, potentially causing large changes in species composition and size distributions within populations. In this study, prey preferences and size-selective predation on zooplankton by Arctic charr were examined in six subarctic lakes with Arctic charr as the dominant pelagic fish species. Most of the lakes had a zooplankton community dominated by copepods (Cyclops scutifer and Eudiaptomus graciloides), but the pelagic charr evidently selected cladoceran species (Bythotrephes longimanus, Daphnia sp. and Bosmina sp.), likely because the copepods have a higher mobility and evasiveness than the cladocerans. Furthermore, a strong size selection was also revealed for both Bosmina sp. and Daphnia sp., as individual prey from Arctic charr stomachs were exclusively larger than individuals sampled in the environment. Additionally, visibility due to size, morphology and pigmentation (egg-carrying females) was also a major factor for the selection of zooplankton prey. In conclusion, Arctic charr was found to be highly selective on zooplankton both in respect to species composition and individual size of Bosmina sp. and Daphnia sp.     

Effects of Daphnia on microzooplankton communities

Intact phytoplankton and microzooplankton communities from eutrophicStar Lake were incubated for 4 days with and without Daphniapulex, Daphnia galeaia mendotae, or a natural assemblage ofDaphnia species. They were sampled at the onset and terminationof the experiment for bacterial, phytoplankton, ciliate, rotifer,copepod and cladoceran densities. The cladocerans had variedeffects on the rotifers, ranging from significant suppressionof most rotifer species (Keratella cochlearis, Polyarthra remata,Keratella crassa) in the D.pulex jars, to the suppression ofone (K.crassa) or no species in the D.galeata mendotae and StarLake Daphnia assemblage jars, respectively. Small ciliates (<30µm, longest dimension), such as Strobilidium sp. and Pseudo-cyclidiumsp., were adversely affected by most of the cladoceran treatments,while several larger ciliates (>81 µm) were unaffectedin all such treatments. Ciliates were not consistently morevulnerable to cladoceran suppression than similarly sized rotifers.The suppression of ciliates and rotifers was attributable toboth direct effects (predation, interference, or both) and indirecteffects (e.g. resource competition) of the cladocerans. ¹Present address: Department of Biology, University of Louisville,Louisville, KY 40292, USA     

Acute toxic impacts of three heavy metals (copper,zinc, and cadmium) on <Emphasis Type="Italic">Diaphanosoma brachyurum</Emphasis> (Cladocera: Sididae)

Diaphanosoma brachyurum (Cladocera: Sididae) is a common limnetic species in summer-temperate and tropical water bodies. Few studies have investigated the sensitivity of D. brachyurum to toxic chemicals despite this species often being dominant in natural lakes and ponds. We performed acute toxicity tests of three heavy metals, copper (Cu), zinc (Zn), and cadmium (Cd), to D. brachyurum. For D. brachyurum, the lethal concentration (LC)₅₀ values of Cu (24-h LC₅₀ = 16.4 μg/L, 48-h LC₅₀ = 10.4 μg/L) and Zn (24-h LC₅₀ = 253.4 μg/L, 48-h LC₅₀ = 174.1 μg/L) were lower than those for D. magna, one of the most used test organisms for toxic chemicals. On the other hand, for D. brachyurum the 24-h LC₅₀ of Cd (166.4 μg/L) was much greater than that for D. magna, and the 48-h LC₅₀ of Cd (69.8 μg/L) was comparable. Our results indicate that D. brachyurum may be more strongly influenced by Zn and Cu than is D. magna. It is likely that the summer plankton community in which Diaphanosoma species is dominant is more sensitive to heavy metals than a community in which Daphnia species are dominant.     

Patterns in the Distribution of Cladocerans (Crustacea: Branchiopoda) in Lakes Across a North–south Transect in Alaska, USA

The remains of cladocerans were examined from the surface sediments of 51 freshwater sites along a north–south transect spanning Alaska. We identified 27 cladoceran taxa from the sediments, consisting primarily of littoral chydorid species. Variations in cladoceran assemblages were related to measured physical and chemical variables using multivariate techniques. Redundancy analysis (RDA) indicated that lake depth, total phosphorus (TP), and altitude all had a significant influence in determining the composition of cladoceran assemblages. Cladoceran communities in tundra and forest-tundra lakes, which were relatively shallow and nutrient-poor, had relatively low abundances of pelagic Cladocera, and were primarily composed of several littoral chydorid species. Among pelagic cladoceran species, there was a distinct shift in dominance from the Bosminidae in lakes in the southern boreal forest region to Daphniidae in lakes in the northern boreal forest. Daphnia dominated lakes had significantly higher total phosphorus, specific conductivity, and calcium concentrations than lakes dominated by Eubosmina. Overall, the relative importance of physical and chemical factors in structuring cladocerans is similar to other previously studied regions, and suggests the Cladocera may be useful as ecological and paleoenvironmental indicators in this region.     

Effect of Aeolosoma sp. (Aphanoneura: Aeolosomatidae) on the Population Dynamics of Selected Cladoceran Species

Although oligochaete worms naturally coexist with cladocerans in many shallow freshwater ponds and lakes, their influence on the latter is not well established. In this work we studied the effect of Aeolosoma sp. on the population growth of Alona rectangula, Ceriodaphnia dubia, Daphnia pulex, Macrothrix triserialis and Moina macrocopa. Population growth studies were conducted at one algal food density (1 × 10⁶cells ml^–1 of Chlorella vulgaris). The experimental design was similar for all five cladoceran species, where we used 100 ml capacity transparent jars containing 50 ml of EPA medium with the desired algal density and three replicates for each treatment. The test medium was changed daily and fresh algal food was added. The initial density of each of the cladoceran species in the population growth studies was 0.4 ind ml^–1 while that of the worms 1.0 ind ml^–1. Following inoculation, we estimated daily the number of cladocerans and the worms for duration of 21 days. Regardless of the presence of worms, Moina macrocopa and Macrothrix triserialis showed rapid population growth while A. rectangula took more than 2 weeks to reach peak abundances. With the exception of M. triserialis, all the other our cladoceran species declined in the presence of Aeolosoma sp. The lowest peak population density (about 1 ind ml^–1) was observed for M. triserialisin controls. The remaining species had peak densities of about 3–5 ind ml^–1. The rates of population increase per day varied from 0.03 to 0.19 depending on the cladoceran taxa and the treatment. In general we found that pelagic taxa were more adversely affected by the presence of the worms than were the littoral cladocerans.     

Species richness of pelagic Cladocera of large lakes in the eastern hemisphere

The composition of the pelagic cladoceran species assemblages in some large, well-studied, lakes of Europe, Asia and Africa is reviewed based on original and literature data. In general, pelagic cladocerans are taxonomically less well studied than some littoral groups. Only the limnetic members of the family Sididae and some Daphnia have recently been revised, whereas knowledge of species diversity of other Daphniidae (including moinas) and Bosminidae is missing. Future detailed taxonomic studies may lead to considerable changes in understanding of limnetic zooplankton composition.