Macrophytes were transplanted into a lowland stream affected by river engineering works. The aim was to analyse the feasibility of their reintroduction and potential to be used for the recovery of the structure and complexity of the lotic habitat. Macrophytes contribute heterogeneity to streams, modify the current velocity, affect sediment and nutrients dynamics, and provide a substrate for epiphytic biofilm. We transplanted specimens of Ludwigia peploides, Gymnocoronis spilanthoides, and Egeria densa into a stream located in the Pampean plain (Buenos Aires, Argentina). The growth and coverage of the transplanted macrophytes and the changes in the structure of the epiphytic biofilm were assessed. The results show that specimens of G. spilanthoides were negatively affected by the transplant and new conditions, E. densa decreased its coverage after the transplant, and L. peploides endured the transplant and adapted to the dredging site with successful establishment and expansion. There were no significant differences between the biofilm developed in L. peploides and G. spilanthoides. Additionally, the biofilm had similar features between the transplanted macrophytes and those from a site with no dredging. Considering this result, the selection between these macrophytes in relation to biofilm production is indifferent. However, as L. peploides adapts better to the new conditions generated by the river engineering works, its use in the rehabilitation project is recommended.Moreover, it is important to consider the ability of different species of macrophytes to survive the transplant and grow under new environmental conditions in order to include them in rehabilitation projects.

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Selection of macrophytes by a generalist invertebrate herbivore and potential impacts for stream rehabilitation.

Lowland streams are usually affected by river engineering works that produce the loss of habitat heterogeneity. Our aim was to assess the transplantation of macrophytes with different complexity into a lowland stream which was dredged and widened. Stuckenia pectinata and Hydrocleys nymphoides were collected at an extraction site and installed at a transplant site. The growth and coverage of macrophytes beds were quantifi ed. Taxonomic richness, Shannon-Wiener diversity, abundance, composition and proportion of functional feeding groups of the macroinvertebrate assemblage presented in macrophyte beds were assessed between sites and species. The growth of both macrophytes did not differ signifi cantly between sites and the coverage of transplanted beds increased, therefore they established at the transplant site within a short period.Regarding to macroinvertebrate assemblage, only the functional feeding groups did not show differences between sites. Moreover, the proportion of predators presented differences between macrophytes at the same site, with H. nymphoides having a higher proportion. Our study showed that this technique is suitable for reintroducing these species and is applicable in rehabilitation projects that promote the restoration of habitat heterogeneity deteriorated by river engineering works. Also, we highlight the importance of incorporate macroinvertebrate functional traits to assess the ecological status after rehabilitation.

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Knowing the interactions between exotic and native species is essential to establish possible threats to the local fauna. In this study, we assessed the use of food resources and diet overlap between a recently introduced snail, Sinotaia quadrata, and a native species, Pomacea canaliculata. We analyzed the gut content and stable isotope of snails and resources in a lowland stream where both species coexist. Both Schoener's and isotope dietary overlap indexes supported dietary overlap. Conversely, gut content analysis showed differences in consumption: S. quadrata consumed more detritus and diatoms than P. canaliculata, whose diet was characterized by detritus and macrophyte remains. Macrophytes were the resource that most contributed to the diet of both species, as shown by stable isotope mixing models. The combination of both techniques, gut content and stable isotope analysis, indicated that S. quadrata consumed macrophyte detritus while P. canaliculata ate fresh macrophytes. This difference indicates differential use of food resources between the studied species coexisting in a lowland stream. Although no negative trophic interaction was found, we highlight the importance of continuing to monitor interactions for other resources and studying possible risks to the local fauna.

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