Phytoplankton–zooplankton dynamics vary with nutrients: a microcosm study with the cyanobacterium Coleofasciculus chthonoplastes and cladoceran Moina micrura

Yan

et al. 2017

Sci Rep

Self Cite

Although the well-known antibiotic norfloxacin (NOR) is recognized as an important environmental pollutant, little is known about its impacts on ecological processes, particularly on species interactions. In this paper, we quantified Daphnia magna (Crustacea, Cladocera) responses in mortality rate at lethal NOR concentrations (0, 25, 50, 100, 200, 300 and 400 mg L−1), and in heartbeat rate, swimming behavior and feeding rate (on the green alga Chlorella pyrenoidosa) at sublethal NOR concentrations (0, 25, 50 and 100 mg L−1) to determine the effects of this antibiotic in plankton systems. In 96-h-long lethal experiment, mortality rates of D. magna increased significantly with increasing NOR concentration and exposure time. In sublethal experiments, heartbeat rate decreased, while time ratio of vertical to horizontal swimming (TVH) and the duration of quiescence increased in D. magna individuals exposed to increasing NOR concentrations after 4 and 12 h of exposure. These collectively led to decreases in both average swimming ability and feeding rate, consistent with the positive relationship between average swimming ability and feeding rate. Overall, results indicate that, by affecting zooplankton heartbeat rate and behavior, NOR decreased feeding efficiency of D. magna even at low doses, therefore, it might seriously compromise ecosystem health and function.

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Lethal/sublethal responses of Daphnia magna to acute norfloxacin contamination and changes in phytoplankton-zooplankton interactions induced by this antibiotic

Yan

et al. 2017

Sci Rep

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“…The initial grazer densities in all treatments were 125 individuals L −1 , which was similar to previous studies addressing cladoceran activities and species interactions 43, 44 , and was within the range observed in natural environments 45 . The initial algal densities in all treatments were approximately 2.5 × 10 4 cells mL −1 , which has been used by many other microcosm experiments 15, 46 . All the beakers were transferred to incubators (TS-2102GZ, Shanghai Anjing laboratory equipment Co., Ltd) that were set at 20 °C with light intensity being about 50 μmol photons m −2 s −1 .…”

Section: Methodsmentioning

confidence: 99%

Microcosm experimental evidence that habitat orientation affects phytoplankton-zooplankton dynamics

Zhang

et al. 2017

Sci Rep

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Although spatial ecology has achieved a great success in the passing decades, the importance of habitat orientation has not been well studied, especially for its effects on prey-predator dynamics. Here, we examined the responses of zooplankton activity and grazing rate to habitat orientation and their consequences on the stability of phytoplankton-zooplankton system in a two-factor factorial experiment involving habitat orientation (three levels; small, medium, and large base area, respectively) and habitat size (64 ml and 512 ml) using two algal-grazer systems (Chlorella pyrenoidosaDaphnia magna and C. pyrenoidosa-Moina micrura). In both systems, grazer density increased with increasing base area for a given chamber volume and with increasing chamber volume for a given orientation in the first 6 days, followed by a dramatic decrease, which corresponded to increasing the amplitude of density fluctuations in both zooplankton and phytoplankton species. Such an algal-grazer dynamics could be accounted for by the greater average swimming ability and grazing rate observed in large-based and large-volumed chambers. Our results demonstrate that habitat orientation affects the zooplankton behavior and population dynamics of both zooplankton and phytoplankton species, which further influences the stability of phytoplankton-zooplankton systems.In natural ecosystems, species habitats may be placed in space with different orientations. For example, either a two-dimensional (e.g. forest patches to bird species; but not a circular habitat) or three-dimensional (e.g. waters for aquatic species; but not a spherical habitat) habitat may be placed in space at different orientations (e.g. angles relative to light direction for two-dimensional habitats and different sides as chamber base for three-dimensional habitats, see Supplementary Fig. S1), even if the habitat size and shape hold constant. Habitat orientations are diverse in natural ecosystems, particularly under human-induced disturbances that often break up a single continuous habitat into several pieces of fragments.Changes in habitat orientation can affect many environmental conditions (e.g. light, water current, heat, wind, nutrients, Earth's gravity and magnetic field) 1, 2 and thus might have consequences on various ecological processes. For example, van Kleunen & Fischer 3 found that habitat orientation (relative to the light direction) plays an important role in determining the morphology of stoloniferous rosette species by varying light intensity in different directions. Community composition of migrating organisms can also be affected by habitat orientation (relative to their moving directions). Generally, habitats oriented perpendicular to the dispersal paths of migrating organisms intercept more species (birds or fishes) and individuals than comparable habitats oriented parallel to the line of travel in both terrestrial 2, 4 and aquatic ecosystems 5 . However, the mechanisms underlying the habitat orientation effects have scarcely been explored, particularly in t...

“…The grazer density is within the range of previous studies addressing species interactions and cladoceran behavior (from 50 individuals/L in Pan et al, 2017, 300 individuals/L in Hurtado-Bocanegra, Nandini, & Sarma, 2002 to 400 individuals/L in Lürling, 2003). The algal density was set relatively low (2.5 × 10 4 cells/ml) to minimize the reaction of positive phototaxis, but it was still above the incipient limiting level for grazer species and has been used by many other microcosm experiments (e.g., Gilbert, 1990;Pan, Zhang, & Sun, 2014).…”

Section: Experimental Designmentioning

confidence: 99%

Habitat orientation alters the outcome of interspecific competition: A microcosm study with zooplankton grazers

Zhang

Sun

2018

Ecology and Evolution

Self Cite

Habitat orientation has recently been demonstrated to affect the foraging behavior, growth, and production of plankton grazers. Because the orientation effect may vary with species, we hypothesize that habitat orientation may alter interspecific interactions between animal species. We experimentally investigated how habitat orientation (placing cuboid chambers in three orientations with long, medium, and small side as the chamber height) affected the interaction between two common cladoceran species, Daphnia magna and Moina micrura, which competitively exploited green algae of Chlorella pyrenoidosa at two volume scales (64 and 512 ml). Results show that chamber orientation and volume additively affected the behavior and species performance of the grazers. Specifically, both grazer species generally decreased their average swimming velocity, grazing rate (on algal cells), body size, and survival and reproduction rates with increasing chamber height for both chamber volumes and with decreasing chamber volume regardless of chamber orientation. Nevertheless, the decrease magnitude was greater for M. micrura with increasing chamber height but was greater for D. magna with decreasing chamber volume. Correspondingly, when cocultured, the density ratio of D. magna to M. micrura increased with increasing chamber height but decreased with decreasing chamber volume. At the end of the experiment, none of D. magna individuals survived in the small and short (large‐based) chambers, and few M. micrura individuals survived in large and tall (small‐based) chambers. These results indicate that both habitat orientation and size affect the outcome of interspecific competition between grazer species. We suggest that variation in habitat orientation may improve community coexistence and species diversity in nature.