Cyprinus carpio has a high environmental impact in the Great Lakes. Realized:
The Common Carp is regarded as a pest fish in part because of its widespread abundance. Common Carp may destroy aquatic macrophytes directly by uprooting or consuming plants (Lee et al. 1980 et seq.), or indirectly by increasing turbidity, thereby reducing light for photosynthesis. This is accomplished by dislodging plants and rooting around in the substrate, thereby deteriorating habitat for species that require vegetation and clean water (Cole 1905; Cahoon 1953; Bellrichard 1996; Laird and Page 1996).
The role of Common Carp as an ecosystem engineer is well documented. For instance, following the installation of a carp barrier at Cootes Paradise Marsh (Lake Ontario), average turbidity was reduced by 40% in open water and 60% in vegetated areas, although further implications for plants and wildlife were difficult to assess due to variation in environmental conditions (Lougheed et al. 2004). Dentler (1993) found that Common Carp feeding behavior can destroy rooted aquatic plants which typically provide habitat for native fish species and food for waterfowl. One study analyzed the relationship between Common Carp biomass, vegetative cover, and waterfowl abundance over time in a shallow inland lake in Illinois (Bajer et al. 2009). The authors found that small densities of Common Carp (<30 kg/ha) did not have significant effects on vegetation or waterfowl, but a subsequent increase to over 250 kg/ha was strongly correlated with a decrease in vegetative cover from its original value of 94% to just 17% (Bajer et al. 2009). Furthermore, waterfowl activity dropped to ~10% of its original value. The authors suggested a threshold of 100 kg/ha past which Common Carp exert extensive ecological damage to shallow lakes (Bajer et al. 2009). In California, Common Carp have been implicated in a decline in water clarity in Clear Lake, Lake County, and in the gradual disappearance of native fishes (Moyle 1976).
A great deal of the Common Carp’s environmental impact is thought to come from indirect effects on habitat and the environment. For instance, in Mexico, populations of a native crayfish (Cambarellus montezumae) notably decreased with increasing carp density (Hinojosa-Garro and Zambrano 2004). However, further analysis indicated that Common Carp was not consuming the crayfish; rather, the destruction and depletion of crayfish habitat by Common Carp, particularly of algal species and macrophytes, were deemed to be the major mechanism of crayfish decline (Hinojosa-Garro and Zambrano 2004).
Miller and Crowl (2006) executed research in a eutrophic lake involving in situ observations of Common Carp impact through the use of cages and exclosures. They documented both direct and indirect effects of Common Carp on overall species composition, abundance, and plant species diversity. Common Carp also appeared to have indirect effects on macroinvertebrate community composition (Miller and Crowl 2006). A similar experiment set up enclosures within experimental ponds and noted that higher biomasses of Common Carp were positively related to phosphorus level, turbidity, and zooplankton biomass and negatively related to abundance of macroinvertebrates and macrophytes (Parkos et al. 2003). In comparison, channel catfish (Ictalurus punctatus), a native benthivore, affected phosphorus concentration and zooplankton communities, but had no significant effect on turbidity, macroinvertebrates, macrophytes, or suspended solids (Parkos et al. 2003).
In a biomanipulative experiment, Schrage and Downing (2004) removed >75% of the Common Carp population in Ventura Marsh, IA. In comparison to the adjacent reference site, they found that the removal of Common Carp had cascading effects, including an improvement in water quality related to decreased suspended solid and phytoplankton biomass. Within a few weeks, the authors noted an increase in Daphnia sp. and Ceriodaphnia sp. biomass as well as macrophyte diversity and density. The major limiting factor on maximum phytoplankton biomass appeared to switch from phosphorus abundance to zooplankton abundance, as suspended inorganic sediment settled to the bottom (Schrage and Downing 2004). Similarly, the eradication of Common Carp from three tributaries of the Bowman-Haley reservoir, North Dakota resulted in upwards of a 50-fold increase in chironomid densities (Bonneau and Scarnecchia 2015).
Common Carp has also been experimentally added to freshwater coastal wetland sites (Delta Marsh, Manitoba, Canada) at densities of 150, 300, 600, and 1200 kg•ha-1 (Badiou and Goldsborough 2010). The authors found that density of Common Carp was positively related to nutrient concentrations in the water column, suspended solids, and chlorophyll a concentrations. Furthermore, carp density was negatively related to dissolved oxygen concentrations, photic depth, and submersed macrophyte density (Badiou and Goldsborough 2010). These findings support the hypothesis that Common Carp may facilitate phytoplankton growth via increased nutrient loading in the water, effectively mimicking the effects of eutrophication (Badiou and Goldsborough 2015). Nevertheless, significant reduction in submersed macrophyte biomass was not observed, possibly because turbidity was relatively limited and the euphotic zone continued to span the entire water column at all carp densities (Badiou and Goldsborough 2010). Their results also suggested that suspension of solids increases as the colonized water body decreases in size, possibly due to a limited prey populations and increased forage activity by Common Carp. In this system, Common Carp populations were estimated to resuspend 37 to 361 kg of sediment per day, relative to pre-stocked conditions (Badiou and Goldsborough 2010). In Kohlman Lake, Minnesota areas with Common Carp increased sediment mixing depths 2.5 times greater (13.0 +/- 3.7 cm) than areas without Common Carp. The increase in mixing depth increased the amount of mobile phosphorus available for release by 55–92%, which could negatively affect the efficacy of nutrient management programs (Huser et al. 2016). Common Carp have been shown to alter bottom-up and top-down processes within freshwater ecosystems. Bottom-up processes are impacted by the alteration of nutrient flows and resuspension of turbidity and top-down are impacted by predation of zooplankton and benthic invertebrates. It can also decrease foraging efficiency of native species by impairing water quality (Weber and Brown 2009).
There is evidence that Common Carp prey on the eggs of other fish species (Moyle 1976; Taylor et al. 1984; Miller and Beckman 1996). For this reason, it may be responsible for the decline of the Razorback Sucker (Xyrauchen texanus) in the Colorado River basin (Taylor et al. 1984). In another case, Miller and Beckman (1996) documented White Sturgeon (Acipenser transmontanus) eggs in the stomachs of Common Carp in the Columbia River. In their review of the literature, Richardson et al. (1995) concluded that Common Carp has had notable adverse effects on biological systems, including the destruction of vegetated breeding habitats used by both fishes and birds. According to McCarraher and Gregory (1970), in 1894 it was documented that endemic Sacramento Perch (Archoplites interruptus) were becoming more scarce because Common Carp was destroying their spawning grounds.
Potential:
Laird and Page (1996) stated that Common Carp may compete with ecologically similar species such as carpsuckers and buffalos. Because this species has been present in many areas since initial surveys were completed, its impacts on many of the native fishes are difficult to determine.
Cyprinus carpio has hybridized with goldfish (Carassius auratus) and, in Europe, with the locally native crucian carp (Carassius carassius). However, Crucian x Common Carp hybrids were found in just 3 of 10 populations in which the two species geographically overlapped (Taylor and Mahon 1977; Hänfling et al. 2005). Cyprinus carpio also hybridized with prussian carp (Carassius gibelio) (Balashov et al. 2017).
The destruction of macrophyte beds in two Spanish lakes by Common Carp negatively impacted the abundance of numerous waterfowl, including ducks, grebes, and flamingos. However, Common Carp served as a food source for gray herons (Ardea cinerea), bolstering their populations (Mediterreana Maceda-Veiga et al. 2017).
A variety of viruses currently infect US populations of Common Carp, including Koi herpesvirus (KHV; cyprinid herpesvirus-3; CyHV-3), carp oedema virus (CEV), Spring viremia of carp (SVC). Infections often lead to mass mortality events in Common Carp (Lovy et al. 2018; Thresher et al. 2018). Infection so far has been limited to Common Carp, but there is uncertainty if any of these viruses could infect new hosts. However, McColl et al. (2017) found no sign of infection or toxic effects of KHV in a wide range of non-target species, including fish, crustacean, amphibian, reptile, and mammals.
Current research on the socio-economic impact of Cyprinus carpio in the Great Lakes is inadequate to support proper assessment.
Realized:
Once established in a waterbody, Common Carp is difficult and expensive to eliminate (e.g., Cahoon 1953). In a study of 129 lakes in Iowa, a negative relationship was discovered between Common Carp and sportfish abundance: (Bluegill (Lepomis macrochirus), Largemouth Bass (Micropterus salmoides), Black Crappie (Pomoxis nigromaculatus), and White Crappie (P. annularis)) (Jackson et al. 2010). This relationship could be due to the poor water quality (e.g., high nutrient levels and low water clarity), which was also associated with high Common Carp abundance; however, Common Carp’s role in the decline of the sportfish populations was not conclusively determined (Jackson et al. 2010).
Common Carp is fished commercially in the Great Lakes (Brown et al. 1999; Dann and Schroeder 2003). However, a recent study of contaminant levels in Lake St. Clair and the St. Clair River indicated that while most carp were below the general human consumption guidelines for mercury content, high PCB levels are of concern for both sensitive and general populations, especially in medium- to large-size fish (Gewurtz et al. 2010). Common carp have been found to contain high concentrations of PCB that are unsafe for consumption, especially within areas of concern in the Great Lakes (Bhavsar et al. 2018).
Anecdotally, Common Carp is widely considered to be a low value “trash” fish in the Great Lakes region. Coupled with real and perceived high contaminant burden, Common Carp is generally considered to be of low or even negative value to sport fishers. Peer-reviewed documentation of this aspect of the socio-economic impact was not able to be found.
Cyprinus carpio has a moderate beneficial effect in the Great Lakes.
Realized:
Common Carp has high lipid content and has been used to test contamination levels in the Great Lakes for comparison with human consumption guidelines (Gewurtz et al. 2010; Pérez-Fuentetaja et al. 2010).
Furthermore, Common Carp is fished commercially in the Great Lakes by both Canada and U.S. (Becker 1983; Brown et al. 1999; Dann and Schroeder 2003). It is also important as ornamental/aquarium fish, particularly if subspecies are considered (koi) (Rixon et al. 2005). It is a popular sport fish in parts of the U.S. According to Scott and Crossman (1973), the recreational pursuit of Common Carp was not considered common in Canadian waters historically, although it has been gaining popularity among anglers and in the tourism fisheries and fish markets in the Great Lakes region. Becker (1983) also described the growing presence of Common Carp in many branches of Wisconsin’s recreational and commercial fisheries.
Common Carp was shown to be an important seed dispersal vector for aquatic plants. However, it may also disperse nonindigenous plants (VonBank et al. 2018). Common Carp may serve as a food source for other organisms, as it was the primary fish consumed by North American river otters (Lontra canadensis) in central Illinois (Fretueg et al. 2015).
Potential:
Common Carp is commonly used in aquaculture in Mexico and Central America, South America, and Eurasia (FAO 2005). Global aquaculture production of Common Carp increased 10.4% per year between 1993 and 2002. At over 33 million tons in 2002, it made up nearly 14% of the global freshwater aquaculture production (FAO 2005). Also, fish oil harvested from Common Carp is a potential feedstock for biodiesel production (Fadhil et al. 2015).