The use of ciliated microeukaryotes and zooplankton in ecotoxicological studies: a look into the future

Aquatic ecosystems have been affected by different human activities (e.g., urbanization, industrial and agricultural activities) and hence, changing the water quality, the process, and function exercised by these environments. The evaluation of water quality through ecotoxicological studies has become an effective tool for understanding the effects of pollutants on biological communities, allowing the measurement of anthropogenic effects on aquatic systems. The use of microeukaryotes ciliates as bioindicators has been identified as a great potential for assessing water quality, however, these organisms are still neglected in ecotoxicological fields being necessary to enlarge the studies with these organisms. Moreover, the interaction effect among more than one environmental stressor (e.g., chemical contaminant, temperature) also needs to be more study due to the complexity of the aquatic ecosystems functioning. In the present study, we demonstrated through three chapters that the microeukaryotes ciliates can be included in the ecotoxicological studies since as long as they are expanded the classical ecotoxicological studies where it is possible to develop standard methods and deepen knowledge. Furthermore, a fourth chapter showed the interaction between more than one environmental stressor could contribute to a biodiversity decline and even, future research should be dedicated to assessing different interactions in the Mediterranean aquatic ecosystems. (Chapter 1) By means of a mini review, and discussed a brief history, the current scenario and pointing out their methodological approaches gaps of the ecotoxicological studies with ciliates. (Chapter 2) Performing a meta-analysis, we assessed the available toxicity data of heavy metals and ciliates. The results showed the tolerance of ciliates to heavy metals varies notably being partly influenced by differences in methodological conditions across studies. Moreover, most ciliates are tolerant to heavy metal pollution than the standard test species used in ecotoxicological risk assessments, i.e., Raphidocelis subcapitata, Daphnia magna, and Onchornyncus mykiss. Finally, this study highlighted the importance of developing standard toxicity test protocols for ciliates, which could lead to a better comprehension of the toxicological impact of heavy metals and other contaminants on ciliate species. (Chapter 3) By means of ecotoxicological tests, this study demonstrated the tolerance of Paramecium caudatum to caffeine. The results showed that this species had higher resistance in the environment. Even, we observed a moderate risk for P. caudatum regarding maximum environmental concentrations of caffeine in surface freshwater being that the global distribution of caffeine and the probability of increasing environmental concentrations highlight the need for more studies to better understand caffeine in aquatic ecosystems and the associated risks. (Chapter 4) Finally, by means of an indoor microcosm experiment, it was demonstrated that the temperature can influence the direct and indirect effects of salinity and pesticides on zooplankton communities in Mediterranean coastal wetlands and highlights vulnerable taxa and ecological responses that are expected to dominate under future global change scenarios.