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Intentional introductions of nonindigenous fishes are increasing globally. While benefits of these introductions are easily quantified, assessments to understand the negative impacts to ecosystems are often difficult, incomplete, or absent. Grass carp (Ctenopharyngodon idella) was originally introduced to the United States as a biocontrol agent, and recent observations of wild, diploid individuals in the Great Lakes basin have spurred interest in re-evaluating its ecological risk. Here, we evaluate the ecological impact of grass carp using expert opinion and a suite of the most up-to-date analytical tools and data (ploidy assessment, eDNA surveillance, species distribution models (SDMs), and meta-analysis). The perceived ecological impact of grass carp by fisheries experts was variable, ranging from unknown to very high. Wild-caught triploid and diploid individuals occurred in multiple Great Lakes waterways, and eDNA surveillance suggests that grass carp are abundant in a major tributary of Lake Michigan. SDMs predicted suitable grass carp climate occurs in all Great Lakes. Meta-analysis showed that grass carp introductions impact both water quality and biota. Novel findings based on updated ecological impact assessment tools indicate that iterative risk assessment of introduced fishes may be warranted. Le nombre d'introductions intentionnelles de poissons non indigenes augmente a l'echelle planetaire. Si les avantages qu'offrent ces introductions peuvent facilement etre quantifies, des evaluations permettant d'en comprendre les impacts negatifs sur les ecosystemes sont souvent difficiles, incompletes ou non existantes. L'amour blanc (Ctenopharyngodon idella) a, a l'origine, ete introduit aux Etats-Unis comme agent de lutte biologique, et des observations recentes d'individus diploides dans le bassin des Grands Lacs ont suscite un interet envers la reevaluation du risque ecologique qu'il presente. Nous evoluons l'impact ecologique de l'amour blanc a la lumiere d'opinions de specialistes et d'un ensemble d'outils et de donnees analytiques les plus recents (evaluation de la diploidie, surveillance basee sur l'ADNe, modeles de repartition des especes (MRE) et meta-analyse). L'impact ecologique de l'amour blanc perqu par les specialistes des peches etait variable, allant d'inconnu a tres fort. Des individus triploides et diploides ont ete captures a l'etat sauvage dans de multiples cours d'eau du bassin des Grands Lacs et la surveillance basee sur l'ADNe donne a penser que l'amour blanc est abondant dans un grand affluent du lac Michigan. Des MRE ont predit que tous les Grands Lacs presentent un climat convenant a l'amour blanc. La meta-analyse montre que les introductions de cette espece ont une incidence tant sur la qualite de l'eau que sur le biote. De nouvelles constatations reposant sur des outils devaluation de l'impact ecologique a jour indiquent qu'il pourrait etre pertinent d'effectuer une evaluation iterative du risque presente par les poissons introduits. [Traduit par la Redaction], Introduction The introduction of nonindigenous species has brought both environmental and economic benefits and harms (Keller et al. 2009). Globally, nonindigenous fishes continue to be introduced for commercial, recreational, or [...]

Trophic cascades, in which changes in predation affect the biomass of lower trophic levels, vary substantially in strength and incidence. Most work to explain this variation has focused on local factors and has ignored larger regional effects. To study how metacommunity dynamics can alter trophic cascades, we constructed mesocosm metacommunities consisting of three pond communities with heterogeneous levels of fish predation and examined how planktonic dispersal rate (5–140% per week) affected biomass partitioning. Two of the three communities differed continually in the occurrence of fish and supported different but constant environments in a ‘spatial trophic cascade,’ while the third community supported temporally variable fish occurrence in a ‘temporal trophic cascade.’ We find that the presence, but the not the magnitude, of dispersal dampens temporal trophic cascades through an increase in grazer biomass. In contrast, dispersal has no effect on the strength of spatial cascades due to strong sorting pressures in the communities with constant presence or absence of fish as top predators. [ABSTRACT FROM AUTHOR]