Direct and indirect effects of an invasive omnivore crayfish on leaf litter decomposition Francisco Carvalho a,b, ⁎, Cláudia Pascoal a,b , Fernanda Cássio a,b , Ronaldo Sousa a,b,c a CBMA — Centre of Molecular and Environmental Biology, Department of Biology, University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal b IB-S, Institute of Science and Innovation for Bio-Sustainability, University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal c Interdisciplinary Centre of Marine and Environmental Research (CIIMAR/CIMAR), University of Porto, Rua dos Bragas 289, P 4050-123 Porto, Portugal HIGHLIGHTS • Procambarus clarkii is one of the most problematic IAS in European freshwa- ters. • We assessed the direct and indirect ef- fects of P. clarkii on leaf decomposition. • P. clarkii affected basal resources by di- rect consumption of leaf litter. • P. clarkii indirectly affected leaf decom- position through invertebrate con- sumption. • Effects of P. clarkii on other inverte- brates may be time dependent. GRAPHICAL ABSTRACT abstract article info Article history: Received 2 September 2015 Received in revised form 24 September 2015 Accepted 24 September 2015 Available online xxxx Editor: D. Barcelo Keywords: Detrital food webs Invasive alien species Litter decomposition Procambarus clarkii Streams Invasive alien species (IAS) can disrupt important ecological functions in aquatic ecosystems; however, many of these effects are not quantified and remain speculative. In this study, we assessed the effects of the invasive cray- fish Procambarus clarkii (Girard, 1852) on leaf litter decomposition (a key ecosystem process) and associated in- vertebrates using laboratory and field manipulative experiments. The crayfish had significant impacts on leaf decomposition due to direct consumption of leaf litter and production of fine particulate organic matter, and in- directly due to consumption of invertebrate shredders. The invertebrate community did not appear to recognize P. clarkii as a predator, at least in the first stages after its introduction in the system; but this situation might change with time. Overall, results suggested that the omnivore invader P. clarkii has the potential to affect detritus-based food webs through consumption of basal resources (leaf litter) and/or consumers. Recognizing that this IAS is widespread in Europe, Asia and Africa, and may attain high density and biomass in aquatic ecosys- tems, our results are important to develop strategies for improving stream ecosystem functioning and to support management actions aiming to control the invasive omnivore P. clarkii. © 2015 Elsevier B.V. All rights reserved. Science of the Total Environment 541 (2016) 714–720 ⁎ Corresponding author at: CBMA — Centre of Molecular and Environmental Biology, Department of Biology, University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal. E-mail address: fcarvalho@bio.uminho.pt (F. Carvalho). http://dx.doi.org/10.1016/j.scitotenv.2015.09.125 0048-9697/© 2015 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv