When contamination acts as chemical barrier isolating populations: applying a new concept of contamination-driven habitat fragmentation in Guadalete River

Abstract

Anthropogenic wastes from different origns (urban, agricultural or industrial activities) have brought severe consequences to the environmental quality of freshwater ecosystems. The impact to aquatic biota linked to contamination has been mainly assessed in function of the toxic (either lethal or sublethal) effects produced on organisms. The ability of organisms to avoid exposure to contaminants, which helps organisms to prevent toxicity, began to be also considered as evidence of environmental risk. The risk associated to the contamination-driven organisms’ spatial displacement can be a serious problem to habitat selection, migration, and (re)colonization processes as well as to the community structure even if no toxic effect at individual level occurs. Theriver inputs of contamination can occur in different zones over its course showing a patchy scenario or a contamination gradient. As organisms exposed to these contamination scenarios can move from contaminated to more favorable habitats, avoiding the contact with the toxic compounds, we have hypothesized that an avoidable discharge can act as chemical barrier causing a habitat fragmentation and affecting the organisms’ displacement (from down to upstream and vice versa). Therefore, the present study aims (i) to verify if the contamination originated from urban and agricultural discharges in a river (i.e. Guadalete River; Southwest Spain) could generate a chemical barrier that restricts the displacement of one of their representative organisms (i.e. the shrimp Atyaephyra desmarestii,and (ii) to discriminate the preference/avoidance response of this species on the effects of the contaminants in water and sediment compartments. Habitat selection assays were performed in a free-choice, multi-compartmented, non-forced exposure system, simulating the spatial arrangement of the samples such as their distribution in the environment, and the freshwater shrimp A.desmarestii, species frequently found in European Rivers (including in the Guadalete River), was used astest organism. Water and sediment samples were collected along Guadalete River, including pristine and sewage-impacted areas (e.g., near the local wastewater treatment plant). Contamination was assessed by measuring a wide range of commonly reported metals and organic contaminants (hydrocarbons, pesticides, pharmceuticals, personal care products, etc.). Results clearly showed that shrimps selected the less contaminated water and sediment samples, indicating that their spatial distribution might be driven by contamination levels. In addition, evidence of habitat fragmentation due to contamination of sediment was observed in the sampling area close to the wasterwater treatment plant. The preference behavior towards some river samples was highly related to contamination levels of water and sediment. Results indicate that contamination might act as chemical barrier causing a spatial isolation of populations.