Trophic Alterations in the Presence of Common Carp

Common carp (hereafter carp) are known to enhance eutrophication in lentic ecosystems.  They have also been shown to severely reduce benthic macroinvertebrate abundances.  Through both of these mechanisms, carp have the potential to cause shifts in invaded systems from one being driven mainly by benthic primary productivity to a system dominated by pelagic primary productivity.  This could have serious consequences for all organisms which rely on these energy pathways, and could ultimately alter the food webs in these systems.  Fish were collected from six shallow reservoirs in eastern South Dakota; three contained carp and three did not.  Age-0 fish were collected in summer and autumn 2010 via daytime electrofishing and adults were collected in spring 2011 via nighttime electrofishing and trap nets.  Tissue samples were collected and used for stable isotope analysis, from which food webs were constructed for each system.  Comparisons between carp and non-carp systems focused on largemouth bass and bluegill because they were present in all systems.  In carp systems, adult and age-0 fish of both species were at lower trophic levels.  Age-0 fish relied more heavily on pelagic derived energy and adults relied more heavily on littoral derived energy, possibly a result of decreased trophic level.