Allelopathic interactions between macrophytes and zooplankton are important to understand the plankton dynamics in shallow waterbodies. Egeria densa is a native, perennial, submerged macrophyte in the tropical

Planktonic cladocerans have evolved different strategies to avoid predation from vertebrates; these include changes in morphology, behavior, physiology, and/or life-history traits. However, littoral cladocerans are better adapted to avoid invertebrate predation particularly from insect larvae by evolving morphological and physiological adaptations. Nevertheless, this has not been proven for some littoral predators such as <em>Hydra</em>. In this study, we provide quantitative data on how <em>Hydra</em> affects its zooplankton prey. We studied the predation behavior on <em>Alona glabra</em>, <em>Ceridodaphnia dubia</em>, <em>Daphnia pulex, Daphnia </em>cf. <em>mendotae, Diaphanosoma birgei, Macrothrix triserialis, Moina macrocopa, Pleuroxus aduncus, Scapholeberis kingi, Simocephalus vetulus, Elaphoidella grandidieri, Brachionus rubens </em>and <em>Euchlanis dilatata</em>. We also tested the indirect effect of allelochemicals from <em>Hydra</em> on the demography of <em>Daphnia </em>cf. <em>mendotae.</em> Littoral cladocerans are specially adapted to resist nematocyst injection and discharge of toxic substances from <em>Hydra</em>. A significant decrease in the population growth rate from 0.21 to 0.125 d^-1 was observed at densities of 2 ind. ml^-1. The role of carapace thickness as an adaptive strategy of littoral cladocerans against <em>Hydra</em> predation is discussed.

No abstract

No abstract

Tropical waterbodies contain several species of toxic cyanobacteria including Microcystis, which adversely affect the somatic growth, survival and fecundity of zooplankton. Scenedesmus, one of the most common green algae, is even found in Microcystis -dominated waterbodies. It is, therefore possible that in natural ponds, rotifers and cladocerans feed on mixed phytoplankton species containing algae and cyanobacteria. In this work, we quantified demographic responses of three rotifer species (Brachionus calyciflorus, B. rubens, and Plationus patulus), and three cladoceran species (Simocephalus mixtus, Daphnia cf. mendotae and Moina macrocopa) fed toxic Microcystis aeruginosa only or mixed with Scenedesmus acutus. The highest population growth for both rotifer and cladoceran species was observed when Scenedesmus was offered alone or at 75 % of the diet. Daphnia cf. mendotae and B. rubens were less affected by Microcystis while M. macrocopa and B. calyciflorus were more adversely influenced, which was also corroborated by life table demography. In competition bioassays, D. cf. mendotae was more efficient, alone or in competition, when fed with 50 or 25 % of Microcystis. This work explains the dynamics of the zooplanktonic community against gradual changes in phytoplankton due to the presence of cyanobacteria.