Ecological Impact of Grass Carp: A Review of the Available Data

The exotic grass carp ( Ctenopharyngodon idella ) has been used for almost a half a century in the United States as a biological agent to control and manage aquatic plants. This long-lived generalist herbivore consumes large amounts of vegetation and can considerably alter habitat and impact aquatic communities. We conducted a literature review to determine whether previous studies adequately addressed ecological impacts of grass carp and their underlying mechanisms. Our goal was to identify strengths and limitations of ecological assessment in the literature and suggest a trajectory of future research. The review yielded 1,924 citations on grass carp; however, data on ecological interactions were limited, and most research emphasized the biology of grass carp or eradication of aquatic plants rather than ecological mechanisms responsible for ecosystem-wide impacts. Very few studies addressed effects on habitat complexity or community-structuring processes. We provide a comprehensive tabulated overview of feeding preferences and environmental impacts of grass carp. We argue that ecology is paramount to evaluating grass carp impacts and thorough understanding of these impacts is essential for the appropriate management of aquatic communities. Current knowledge is not sufficient to accurately predict long-term effects of grass carp on freshwater ecosystems. We advise a more cautious approach to developing guidelines for grass carp use.