Growth-enhanced salmon modify stream ecosystem functioning

Abstract

Use of fast-growing domesticated and/or genetically modified strains of fish isbecoming increasingly common in aquaculture, increasing the likelihood of deliberateor accidental introductions into the wild. To date, their ecological impacts on ecosys-tems remain to be quantified. Here, using a controlled phenotype manipulation byimplanting growth hormone in juvenile Atlantic salmon (Salmo salar), we found thatgrowth-enhanced fish display changes in several phenotypic traits known to beimportant for ecosystem functioning, such as habitat use, morphology and excretionrate. Furthermore, these phenotypic changes were associated with significantimpacts on the invertebrate community and key stream ecosystem functions such asprimary production and leaf-litter decomposition. These findings provide novel evi-dence that introductions of growth-enhanced fish into the wild can affect the func-tioning of natural ecosystems and represent a form of intraspecific invasion.Consequently, environmental impact assessments of growth-enhanced organismsneed to explicitly consider ecosystem-level effects.