The feeding rates and functional responses of the copepod Mesocyclops pehpeiensis (adult females) were quantified using rotifers (Brachionus rubens, Brachionus havanaensis and Plationus patulus), cladocerans (Moina macrocopa, Ceriodaphnia dubia and Alona glabra), the green alga Chlorella vulgaris and the cyanobacterium Anabaena sp. as food. Mesocyclops pehpeiensis showed preferences for B. havanaensis, B. rubens and M. macrocopa when offered mixed rotifer and cladoceran species. Functional response curves showed increased consumption with increasing density of B. rubens in the medium until about 160 ind. 40 ml⁻¹ of prey, and thereafter reached an asymptote. In general, regardless of water temperature, prey consumption was higher in the absence of algae in the medium. Consumption was highest at 35°C and declined with decreasing temperatures. Ingestion rates of the alga and cyanobacterium showed maxima at 25°C. Our results also indicated that M. pehpeiensis is an omnivore, consuming phytoplankton and zooplankton.

Controlling noxious phytoplankton blooms by biomanipulation largely depends on the presence of large-sized (>3000 µm) generalist grazers, not common in the tropics. Therefore, we compared the ability of small (≤2000 µm) microcrustaceans Ceriodaphnia dubia, Moina macrocopa, Daphnia pulex, Simocephalus vetulus and Heterocypris incongruens to feed and grow on cyanobacterial diets. We studied their feeding preferences on phytoplankton from natural lake water with a dominance of Microcystis sp., Fragilaria sp. or Planktothrix sp. to which we added Scenedesmus acutus. Also tested were the ability of D. pulex, S. vetulus and H. incongruens to reduce cyanobacterial densities by grazing, and the rate of grazing and demographic responses of S. vetulus and H. incongruens on diets of S. acutus, Microcystis sp. and Planktothrix sp. All species fed on small colonies of Microcystis sp., but not on filamentous Planktothrix sp. or colonial Fragilaria sp. Simocephalus vetulus and H. incongruens were generalists and most capable of reducing cyanobacterial densities. Demographic variables of S. vetulus, but not H. incongruens, were significantly lower on the cyanobacterial diet; for instance, the population growth rates were between 0.07–0.2 day⁻¹ on cyanobacterial diets, but 0.31 on S. acutus while for H. incongruens they ranged between 0.07 and 0.08 day⁻¹, regardless of whether the diet was a cyanobacteria or S. acutus. Our study warrants further tests on the ostracod H. incongruens in order to test its efficacy in reducing cyanobacterial densities in shallow tropical ponds.

The present long-term (1993–2013) study was aimed at identifying the effects of global change on the environmental characteristics and the plankton community of the tropical, high-altitude Lake Alchichica, Puebla, Mexico. We found no statistically significant increasing trend in air temperature, but an increase from 2002 to 2013, and interannual variability in the meteorological variables. Accordingly, the water temperature rose from 1993 to 2003 and remained similar until 2013. Nonetheless, on a longer-term (1966-2018), longer than the period considered in the present study, air and water temperatures showed an increasing trend in the range considered indicative of climate change. The lake displayed a characteristic warm monomictic thermal pattern but exhibited interannual variability. The planktonic community composition and structure remained similar. The small chlorophytes (e.g., Monoraphidium minutum) dominated the phytoplankton abundance, while the large diatom Cyclotella alchichicana dominated the biomass. The calanoid copepod Leptodiaptomus garciai dominated both the zooplankton abundance and biomass. However, as the temperature increased the large-size phytoplankton (i.e., C. alchichicana) abundance and biomass increased, but the small-size phytoplankton abundance and biomass, as well as the adult copepod abundance and biomass, decreased. The increase in temperature could have favoured the large-size over the small-size phytoplankton. In addition, the temperature increase could have negatively affected the calanoid copepods in two different ways—direct association with the negative effects of higher temperatures on the physiology of the copepods, or indirect association with the negative effects of higher temperatures on the small-size phytoplankton, which diminish the copepods’ food resource.