The role of subtropical zooplankton as grazers of phytoplankton under different predation levels
Lacerot, G. ; Kruk, C. ; Lurling, M. ; Scheffer, M. - \ 2013
Freshwater Biology 58 (2013)3. - ISSN 0046-5070 - p. 494 - 503.
fish community structure - shallow lakes - jenynsia-multidentata - trophic interactions - size distribution - biomanipulation - dynamics - climate - restoration - cladocerans
1.Large zooplankton such as Daphnia play a fundamental role as consumers of phytoplankton in temperate lakes. These organisms are scarce in subtropical lakes where smaller cladocerans or copepods take this niche. However, such smaller grazers appear to be less able to exert an effective top-down control on the phytoplankton community. 2.We experimentally analysed the ability of zooplankton typical of subtropical, nutrient-rich lakes to graze effectively on the phytoplankton community. We conducted two outdoor mesocosm experiments in a hypertrophic lake, with combinations of three different zooplankton densities and three different omnivorous fish densities. In the first experiment, the zooplankton community was dominated by a small-sized cladoceran (Moina micrura) and in the second by a calanoid copepod (Notodiaptomus incompositus). The phytoplankton community also differed between experiments, with dominance of large size classes and less palatable species in the first experiment and edible sizes in the second. 3.In both experiments, the effect of fish on the largest zooplankton was strong and negative, and low fish densities were sufficient to eliminate the larger zooplankton. Fish presence had positive effects on the biovolume of the largest phytoplankton size fraction (30-100µm) in the first experiment. This effect was more pronounced in combination with high zooplankton biomass, suggesting that nutrient recycling by both fish and zooplankton may have been an important mechanism promoting phytoplankton growth. 4.None of the zooplankton communities tested had significant top-down effects on the phytoplankton community. In view of the phytoplankton species that dominated the communities at the end of both experiments, inedibility, toxicity and antigrazer defences may explain the absence of significant effects of zooplankton grazing. 5.Our results support the idea that in subtropical nutrient-rich lakes, drastic removal of small omnivorous fish may be needed to allow an increase in zooplankton biomass. In addition, our results imply that for such a change to result in effective top-down control of phytoplankton, a shift in zooplankton community composition is essential too, as the experimental increase in small-sized grazers had little effect on the phytoplankton communities.
The good, the bad and the plenty: interactive effects of food quality and quantity on the growth of different Daphnia species
Bukovinszky, T. ; Verschoor, A.M. ; Helmsing, N.R. ; Bezemer, T.M. ; Bakker, E.S. ; Vos, M. ; Domis, L.N.D. - \ 2012
PLoS ONE 7 (2012)9. - ISSN 1932-6203 - 8 p.
life-history - fresh-water - aquatic herbivores - body size - stoichiometry - zooplankton - limitation - performance - diets - cladocerans
Effects of food quality and quantity on consumers are neither independent nor interchangeable. Although consumer growth and reproduction show strong variation in relation to both food quality and quantity, the effects of food quality or food quantity have usually been studied in isolation. In two experiments, we studied the growth and reproduction in three filter-feeding freshwater zooplankton species, i.e. Daphnia galeata x hyalina, D. pulicaria and D. magna, on their algal food (Scenedesmus obliquus), varying in carbon to phosphorus (C:P) ratios and quantities (concentrations). In the first experiment, we found a strong positive effect of the phosphorus content of food on growth of Daphnia, both in their early and late juvenile development. Variation in the relationship between the P-content of animals and their growth rate reflected interspecific differences in nutrient requirements. Although growth rates typically decreased as development neared maturation, this did not affect these species-specific couplings between growth rate and Daphnia P-content. In the second experiment, we examined the effects of food quality on Daphnia growth at different levels of food quantity. With the same decrease in P-content of food, species with higher estimated P-content at zero growth showed a larger increase in threshold food concentrations (i.e. food concentration sufficient to meet metabolic requirements but not growth). These results suggest that physiological processes such as maintenance and growth may in combination explain effects of food quality and quantity on consumers. Our study shows that differences in response to variation in food quality and quantity exist between species. As a consequence, species-specific effects of food quality on consumer growth will also determine how species deal with varying food levels, which has implications for resource-consumer interactions
Temporal and spatial distribution of microcrustacean zooplankton in relation to turbidity and other environmental factors in a large tropical lake (L. Tana, Ethiopia)
Dejen, E. ; Vijverberg, J. ; Nagelkerke, L.A.J. ; Sibbing, F.A. - \ 2004
Hydrobiologia 513 (2004)1-3. - ISSN 0018-8158 - p. 39 - 49.
barbs barbus-humilis - aquatic organisms - suspended clay - population-dynamics - community structure - reservoir - reproduction - cladocerans - abundance - dispersal
The spatial and seasonal distribution of microcrustacean zooplankton of Lake Tana (Ethiopia) was monthly studied for 2 years. Concurrently, various environmental parameters were measured and related to zooplankton distribution. Canonical Correspondence Analysis (CCA) was used to estimate the influence of abiotic factors and chlorophyll a content in structuring the zooplankton assemblage. Among the environmental factors, zooplankton abundance correlated most strongly with turbidity. Turbidity was negatively correlated with species abundance, especially for Daphnia spp. and to the least extent for Diaphanosoma spp. Analysis of variance (ANOVA) was used to determine spatial (littoral, sublittoral and pelagic zone) and temporal (four seasons) variation in zooplankton abundance. We observed significant temporal differences in zooplankton abundance, with highest densities during dry season (November-April). Only cladocerans showed significant differences in habitat use (highest densities in the sublittoral zone).
Life-history characteristics of Daphnia exposed to dissolved microcystin-LR and to the cyanobacterium microcystis aeruginosa with and without microcystins
Lürling, M.F.L.L.W. ; Grinten, E. van der - \ 2003
Environmental Toxicology and Chemistry 22 (2003)6. - ISSN 0730-7268 - p. 1281 - 1287.
toxic cyanobacteria - food ingestion - fatty-acids - inhibition - pulex - growth - blooms - water - lake - cladocerans
In the current study, the role of microcystin(MC)-LR in inhibiting Daphnia growth was examined. Somatic growth, time to first reproduction, number of newborns, mortality, and population growth were measured in Daphnia fed mixtures of the cyanobacterium Microcystis aeruginosa (with and without microcystin) with a high quality green algal food (Scenedesmus obliquus) to avoid nutritional deficiency. Microcystin-LR-containing cells caused a dramatic reduction in growth and resulted in death of the animals, but the addition of purified toxin (microcystin-LR) had no effect on Daphnia growth. In contrast with the nutritional inadequacy hypothesis, growth on a mixture of Scenedesmus and the microcystin-free food was significantly reduced. This observation could not be explained from morphological characteristics of the strains that were uni- and bicellular. Clearance rates of Daphnia fed mixtures of Microcystis and Scenedesmus were significantly lower than rates of animals fed solely Scenedesmus. The results of an additional life-history experiment with different quantities of Scenedesmus could not reject the hypothesis that reduced feeding may be the causal factor in explaining reduced Daphnia growth on the food mixture with microcystin-free Microcystis. Thus, feeding inhibition should be considered in explaining the food quality of Microcystis and other cyanobacteria, as it could affect the total food intake and consequently Daphnia growth.
Effects of Microcystin-free and Microcystin-containing strains of the Cyanobacterium Microcystis aeruginosa on growth of the grazer Daphnia magna
Lürling, M.F.L.L.W. - \ 2003
Environmental Toxicology 18 (2003). - ISSN 1520-4081 - p. 202 - 210.
life-history - toxic microcystis - food ingestion - green-alga - pulex - zooplankton - inhibition - survival - blooms - cladocerans
Harmful effects of the common bloom-forming cyanobacterium Microcystis aeruginosa on the grazer Daphnia have been explained from morphological features, nutritional insufficiency, and the production of toxins called microcystins. The effects of four M. aeruginosa strains, including one free of microcystins, on the growth of Daphnia magna were examined. Population growth was measured in Daphnia fed each M. aeruginosa strain alone and fed mixtures of each strain with the green alga Scenedesmus obliquus to avoid nutritional deficiency. The presence of Microcystis in the food resulted in decreased Daphnia population growth rates. A significant correlation (P <0.001) was found between the amount of microcystins (MC) in the food and the population growth rate, but growth inhibition in Daphnia fed with the MC-free strain could not be explained by the toxicity of the microcystins. Inasmuch as there was greater reduction in growth of the Daphnia fed mixtures of the MC-free strain with Scenedesmus than of the Daphnia fed only the same amount of Scenedesmus as in the mixtures, other factors associated with this Microcystis strain must have inhibited growth. However, morphology and nutritional insufficiency could be excluded as causal factors. The strong relationship between Daphnia feeding activity and population growth suggests that feeding inhibition may have caused the observed detrimental effects on the animals. (C) 2003 Wiley Periodicals, Inc.