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.     

Effects of interference and exploitative competition from large-bodied cladocerans on rotifer community structure

I examined the effects of a graded density of the large-bodied cladoceran Daphnia pulicaria upon a natural rotifer assemblage to assess the relative magnitudes of interference and exploitative competition. An in situ, 5-day, bag-enclosure experiment was conducted to test the hypothesis that populations of the rotifers Anuraeopsis spp., Keratella cochlearis typica and Polyarthra spp. are differentially suppressed by interference competition. Rotifer density decreases and observed vs. expected mortality rates for all three rotifer taxa were consistent with the hypothesis of suppression via interference competition. Evidence of exploitative effects were also apparent, though interference effects appeared more important at higher cladoceran densities.     

Spring-Summer Succession of Planktonic Rotifers in a South Andes Lake

The dynamics of planktonic rotifer in Laguna Ezquerra (Rio Negro, Argentina) was studied from October 1988 to March 1989, in relation to food resources and cladoceran populations. During the spring and summer period, total rotifer density differed markedly. In spring rotifer populations remained at low density and an inverse relationship with cladoceran biomass was found. In contrast, in summer, the rotifer densities increased greatly and a positive relationship with cladoceran biomass was observed. Food resources decreased during mid January and this seemed to give rotifers a competitive advantage over cladocerans. Bosmina longirostris and Ceriodaphnia dubia were both present during the spring, but only Bosmina prevailed in summer. The composition of cladoceran assemblages together with food resources seem to be an important factor in rotifer dynamics.     

The susceptiblity of Keratella cochlearis to interference from small cladocerans

SUMMARY. 1. Even at high population densities (300–2000 ind. 1⁻¹), only one of five small cladoceran species (adult body length <1 mm) significantly suppressed population growth of the rotifer Keratella cochlearis through interference (encounter) competition. At 500 ind. H, adults of D. ambigua (0.96 mm body length) imposed an instantaneous per capita death rate of 0.21 day⁻¹ on this rotifer. These short-term experiments may have underestimated cladoceran interference because newborn rotifers were rarely present.
2. Newborn rotifers (<12 h old) were much more susceptible than adult rotifers (> 24 h old) to interference from Ceriodaphnia dubia. All of the small cladoceran species tested were very much less likely than large Daphnia (body lengths >1.2 mm) to interfere with K. cochlearis , but perhaps at high population densities they could suppress population growth of susceptible rotifer species by damaging, and possibly eating, relatively small and soft-bodied newborn individuals.
3. K. cochlearis of the tecta form, without a posterior spine, produced offspring of the typica form, with a posterior spine, in the presence of C. dubia. This developmental response is stimulated by at least several, and possibly all, cladocerans and probably reduces the susceptibility of the rotifer to cladoceran interference.     

Influence of overwinteringDaphnia on spring zooplankton communities: An experimental study

To evaluate the influence of overwintering individuals of zooplankton on spring zooplankton communities, the dynamics of zooplankton communities with or without overwintering individuals were observed in experimental ponds from fall to spring. An insecticide, carbaryl, was used to regulate the overwintering individuals. In ponds which received insecticide applications in November or January, all cladoceran and rotiferan species were eliminated by the treatments and did not reappear until late March or early April, even when the chemical disappeared rapidly. The low water temperature may delayed the establishment of the populations from resting eggs. In these ponds, populations of various cladoceran and rotiferan species, which seemed to be originated from resting eggs, were built up in the spring. In control ponds,Daphnia ambigua orD. longispina overwintered as juveniles and adults and established a large spring population earlier than other cladocerans and rotifers overwintering as resting eggs. The latter zooplankters did not increase in the spring probably because their growth was suppressed by the precedingDaphnia species through competition. In nature, even if the number of overwintering individuals is small, they may have a potential to build up a large population earlier than the individuals hatching from resting eggs. As a result, the species which have overwintered as individuals seem to predominate in the spring and have a large influence on the spring zooplankton community.     

Increasing dominance of small zooplankton with toxic cyanobacteria

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Relative vulnerabilities of natural rotifer and ciliate communities to cladocerans: laboratory and field experiments

SUMMARY. 1. Two experiments with plankton communities from Storrs Pond (NH), one conducted in the laboratory and one in field enclosures, assessed the impact of different cladocerans on rotifers and ciliated protozoa.
2. The smallest cladoceran, Bosmina longirostris , did not depress rotifer or ciliate growth rates while the intermediate sized dadoceran, Daphnia galeata mendotae , reduced ciliate growth rates in the enclosure experiment but had only a marginal effect in the jar experiment. D. galeata mendotae had no effect on any of the rotifers in either experiment.
3. In both experiments the largest cladoceran, Daphniapulex , depressed the growth rates of ciliates and those rotifers known to be vulnerable to interference competition. Polyarthra vulgaris , previously shown to be resistant to cladoceran interference, was the only rotifer unaffected by D. pulex in the field experiment but was depressed by the much higher densities of this cladoceran in the laboratory experiment.
4. Cladocerans did not affect phytoplankton or bacterioplankton abundance in either experiment. Therefore the mechanism most likely to be responsible for the suppressive effect of cladocerans on rotifers and ciliates in these experiments is direct mechanical interference or predation, rather than exploitative competition.     

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.     

Contrasting Zooplankton Assemblages in Two Oxbow Lakes with Low Transparencies and Narrow Emergent Macrophyte Belts (Krapina River,Croatia)

The aim of this study was to examine the combined effect of water transparency and narrow macrophyte belts on zooplankton assemblages in two oxbow lakes (Krapina River, Croatia). Samples were collected in open water and among helophytes in the littoral zone from April until September 2008. Rotifers were the most abundant group of zooplankton in both lakes, and dominated in the Krapina oxbow lake 1 (KO1). Lake KO1 had significantly lower transparency, lower percentage macrophyte cover and higher chlorophyll a concentration than Krapina oxbow lake 2 (KO2). In lake KO1, variation in the horizontal distribution of cladocerans and rotifers in terms of their abundance seemed to be determined by competition between Bosmina longirostris and Keratella cochlearis, initiated by oscillation in transparency and detritus availability. In lake KO2, with higher transparency and higher percentage macrophyte cover, the abundance of small‐ and large‐bodied cladocerans increased in the littoral zone simultaneously with higher transparency, suggesting fish predation. Results of this study indicated that small differences in transparencies between the two lakes caused significant differences in horizontal distribution of the zooplankton assemblage. Even narrow helophyte belts offered a refuge to zooplankton, although lower transparencies reduced the effectiveness of macrophytes as a refuge from predators. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Competitive interactions between the rotifer Synchaeta oblonga and the cladoceran Scapholeberis kingi Sars

Competition experiments showed that the small cladoceran Scapholeberis kingi rapidly excluded the rotifer Synchaeta oblonga from mixed-species cultures, but was itself unaffected by the presence of S. oblonga. Short-term experiments testing the effect of S. kingi on the survivorship and reproduction of S. oblonga showed that the former imposed a high mortality on the latter, even though shared food resources were abundant. These results indicate that adult S. kingi mechanically interferes with S. oblonga either by ingesting, or by rejecting in a damaged condition, individuals swept into its branchial chamber. In contrast to many other small species of cladocerans, and like large species of Daphnia, S. kingi has the potential to markedly suppress populations of some rotifer species through a combination of interference and exploitative competition.     

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).     

The diet of Abramis brama (L.) larvae reared in illuminated cages

The paper presents the results of investigations on the feeding of bream larvae reared in illuminated cages in a mesotrophic lake. The same species of zooplankton were found in both the lake and the fish cages. Copepoda predominated in abundance and biomass. During the mixed feeding the bream larvae diet consisted of rotifers (45.8%), small cladocerans (41.6%) and phytoplankton (13.6%). According to Ivlev's selectivity indices (E), the most important food species were: Keratella cochlearis (E = +9.94), Kellicotia longispina (E = +0.93), K. quadrata (E = +0.92), Bosmina longirostris (E = +0.92), Trichocerca sp. (E = +0.89), and Chydorus sphaericus (E = +0.88). The total length (TL) of bream larvae consuming their first nauplii and copepodites of Copepoda was 8.9 mm. As bream larvae grew, cladocerans were more often selected than rotifers. Copepods usually made up an insignificant component of the diet. Bream larvae in illuminated cages generally fed at night; their alimentary tracts were filled to the maximum in the period from sunset to sunrise. Indices thereof reached 755.6 at night and 278.0 ? in the daytime.     

轮虫和枝角类的种间竞争及其影响因子研究进展

轮虫和枝角类是浮游动物群落的重要组成部分和优势类群,它们之间的竞争互作是调节水生态系统结构和功能的主要动力之一。普遍的观点认为,轮虫和大型枝角类难以共存,往往被竞争排斥,而和小型枝角类可以共存;实际上,轮虫和枝角类的种间竞争结局存在一定的不确定性。介绍了轮虫和枝角类的种间竞争方式及其相对重要性,对影响轮虫和枝角类种间竞争结局的因素,包括温度、食物、相对起始密度、个体大小、食物临点、耐饥饿能力、捕食及竞争者和捕食者释放的化感物质等,进行了系统的梳理和分析,并提出了今后亟待解决的科学问题和研究切入点。     

Effect of the epizoic rotifer Brachionus rubens on the population growth of three cladoceran species

Using population densities and growth rates as criteria, we studied interactions between the epizoic rotifer Brachionus rubens and each of three cladoceran species differing in size and reproductive rates — Daphnia carinata, Moina macrocopa and Ceriodaphnia rigaudi. In all mixed — species experiments, B. rubens existed in both the epizoic mode, attached to the cladoceran host, and in the free-swimming mode. Rotifer population growth rates were significantly depressed in the presence of M. macrocopa, presumably as a consequence of exploitative and interference competition. The largest cladoceran, D. carinata probably did not suppress B. rubens, because the epizoic component of the rotifer population escaped from the deleterious effects of mechanical interference. Peak population numbers and initial population growth rates reached by all three cladocerans were lower in the presence of B. rubens, probably because of the adverse effects of the epizoic infestation, which was maximal on D. carinata and least on C. rigaudi. In mixed-species cultures of D. carinata and M. macrocopa, the presence of B. rubens helped D. carinata coexist with M. macrocopa, which otherwise would have suppressed the Daphnia.     

Competitive ability of Daphnia under dominance of non-toxic filamentous cyanobacteria

It is generally assumed that Daphnia is more susceptible to the inhibitory effects of filamentous cyanobacteria than small cladocerans since daphnids have a larger gape size and filtrate the filaments, whereas small cladocerans do not. This study addresses the question whether food limitation has the potential to modify this scenario of cladoceran response to dominance of non-toxic filamentous cyanobacteria. Daphnia galeatawas grown under limited (0.1 mg C l^–1) and unlimited concentrations (1.0 mg C l^–1) of high-quality food algae both in the absence/presence of non-toxic filamentous Aphanizomenon flexuosum. As the effects of these cyanobacteria on D. galeatawere positive under food limiting conditions and negative at the high food density, it was concluded that D. galeatawas mainly affected by nutritional quality due to its ability to ingest the filaments, while mechanical interference with food collection was not important. In competition experiments between D. galeataand Bosmina longirostris, D. galeatawas the dominant species at regular additions of food (1.0 mg C l^–1) in the absence of Aphanizomenon. In the presence of these cyanobacteria, D. galeatawas inhibited during the first days of the experimental period. However, the negative effect at the initially high food density was outweighed by nutrition at food limiting conditions and the outcome in competitive dominance was not changed. The results demonstrate that the ability of D. galeata to ingest large-sized non-toxic cyanobacteria can be considered as advantageous under food limiting conditions.     

Susceptibilities of different-sized ciliates to direct suppression by small and large cladocerans

• 1 Laboratory experiments compared the susceptibilities of six ciliates and the rotifer Keratella cochlearis to predation and interference from Daphnia pulex and Bosmina longirostris.
• 2 Susceptibilities of the ciliates to D. pulex were similar to or less than that of the rotifer, and decreased with increasing ciliate size. Most ciliates were just as susceptible to B. longirostris as to the much larger D. pulex. The jumping response of the oligotrich Strobilidium gyrans appeared to be an effective defence against B. longirostris.
• 3 Clearance rates of B. longirostris and D. pulex on different ciliate species at a density of 1,3 ciliates ml^?1 ranged from 1–30 to 5–24ml ind.^?1 day^?1, respectively. In natural plankton communities, cladocerans could impose high mortality rates on ciliates and shift the size structure of ciliate assemblages towards larger and less susceptible species.

     

Chemical interference by Daphnia on Keratella: a life table experiment

Daphnia can suppress rotifers through mechanical interference(interference competition) and exploitative competition. Totest chemical interference (interference competition) by Daphniaon the rotifer Keratella, life history characteristics wereanalysed for Keratella cochlearis in the presence and absenceof Daphnia-mediated chemicals. The presence of Daphnia-mediatedchemicals induced a lower fecundity and a decrease in the intrinsicrate of population growth. This type of interference competitionshould affect the composition of natural rotifer communitiesregardless of mechanical interference and exploitative competitiondue to Daphnia.     

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     

Prey handling time and ingestion probability for Mesocyclops sp. predation on small cladoceran species Bosmina longirostris, Bosminopsis deitersi, and Scapholeberis mucronata

We compared the vulnerability of small cladoceran species (Bosminopsis deitersi, Bosmina longirostris, and Scapholeberis mucronata) to predation by Mesocyclops sp. in the laboratory based on prey handling time and ingestion probability. We also estimated the effects of ontogenetic changes on handling time by testing prey of various body sizes. All tested prey species showed an increasing pattern of handling time along with growth (increase of body size). For juveniles smaller than 0.3mm, the prey handling time was similar for B. deitersi and B. longirostris, but markedly longer for S. mucronata. Mesocyclops sp. rejected large (>0.35mm) B. longirostris and S. mucronata soon after capture and consequently showed a low probability of successful ingestion, whereas most large individuals of B. deitersi were consumed. The shorter handling time and higher ingestion probability of small juveniles indicate that the copepods ingest small juveniles more efficiently than larger individuals. Thus, it seems that the vulnerability of small cladocerans to copepod predation differs ontogenetically, with the greatest vulnerability being during the juvenile period. The ontogenetic reduction in the vulnerability of B. longirostris and S. mucronata was shown in the rapidly reduced ingestion probability as well as by the increase in prey handling time for large individuals. The results show that the vulnerability to predation by copepods of B. longirostris and S. mucronata reduces more quickly with increasing size than does that of B. deitersi, and it seems that the former two species are more resistant to copepod predation.     

The development and reproductive output of three species of Cladocera (Crustacea,Branchiopoda) with different size spectra as the result of vertebrate and invertebrate predation impact

Seasonal changes in development and reproduction of three species of Cladocera, Bosmina longirostris, Bosmina coregoni and Diaphanosoma brachyurum, were studied in regard to impact of vertebrate (planktivorous fish) and invertebrate (cladoceran Leptodora kindtii and cyclopoid copepods Mesocyclops leuckarti and Thermocyclops oithonoides) predators. Each of the cladocerans represented a different prey type. The population of the largest body-sized D. brachyurum was not affected by predators suggesting unidentified mechanisms of predation-avoidance. Diaphanosoma displayed low reproductive output coinciding with high density. Medium-sized B. coregoni, influenced by planktivorous fish, invested in reproduction and carried large egg-clutches resulting in gradual increase in population density. The population of small body-sized B. longirostris, that was influenced by invertebrate predators, displayed high density and reproductive effort in spring, followed by extreme collapse in abundance and reproduction during summer months. The results suggest that invertebrate predators may suppress populations of some Cladocera more strongly than planktivorous fish.