A new perspective of environmental stress in heterogeneously contaminated landscapesbeyond the individual effect
he use of chemical products for human health, agricultural, and industrial activities is steadily increasing worldwide. These chemicals and their metabolites can be released either- directly or indirectly- into aquatic environments, leading to negative impacts on aquatic biota. To detect the effects of contaminants on organisms and to support ecosystem protection, Environmental Risk Assessment (ERA) has traditionally relied on forced exposure approaches, in which organisms are continuously exposed to contaminants. While useful, this method overlooks the connectivity among habitats and the spatial heterogeneity of contamination. In natural systems, habitats are not uniformly contaminated and are often interconnected, allowing many organisms to migrate between them in search of more favorable conditions. Therefore, it is essential to broaden the framework through which toxicity is assessed. A recently developed, non-forced exposure approach- reflecting natural environmental connectivity- offers an ecologically relevant means of evaluating the consequences of pollution in chemically heterogeneous aquatic ecosystems. This method integrates novel ecological concepts into ERA, including avoidance/repellence and preference behaviors (from a habitat selection perspective), the meta-ecosystem framework (considering habitat heterogeneity and connectivity), colonization (focusing on ecosystem recovery and attractiveness), and habitat fragmentation (recognizing that chemical barriers can isolate populations spatially). In the present PhD study, it has been hypothesized that contamination in aquatic environments may interfere with the organisms' habitat selection process and alter the natural response of organisms to a stressor. However, it is difficult to simulate chemically heterogeneous habitats, which are connected and that can be selected by organisms. Therefore, different scale multi-compartmented systems (HeMHAS- Heterogeneous Multi-Habitat Assay System) were built to provide organisms with the necessary conditions to test the effect of contamination considering the ecological interactions in a spatially broader and connected landscape. The primary objective was firstly to assess to what extent the contaminants are crucial in the decision of the organisms to stay in, or avoid, a habitat; secondly, to assess the individual (biochemical/physiological damage to organisms) and ecological (changes in the community structure) consequences due to an organism's decision to stay or not in a contaminated environment. Different chemical contaminants covered various modes of primary action like metals (copper), contaminants of emerging concern (CEC) (ibuprofen, irgarol, terbuthylazine) and antidepressants (fluoxetine) were used in this study. Regarding the test species, different model organisms of shrimps and fish were tested. We found that the tested chemicals have deleterious effects on the aquatic ecosystem. These contaminants cause both behavioral and biochemical changes in aquatic organisms. Organisms (fish and shrimp) studied in this experiment were able to avoid contaminants gradients in different ways. The avoidance behavior of species might depend on a cost-benefit balance between the risk of predation and exposure to the contaminants as well as chemicals mode of action. The study suggested that the avoidance/colonization pattern of species could jeopardize population persistence and species' habitat selection thereby indicating that contaminants may strongly affect interspecies relations. By using a mesocosm approach, the study also showed how contamination effects can be assessed in the HeMHAS combining effects on the structure and functioning and ecological relationships of ecosystems. The study highlighted the potential use of the HeMHAS system as a valuable tool to investigate and gain insights into the behavioral responses of organisms to various contaminants. The implementation of this work will help to protect, conserve and restore aquatic ecosystems, to avoid their deterioration, to understand the effects of contamination from a landscape perspective and to preserve the ecosystems' resources and services.
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