Disturbances can lead to non-random changes in community composition due to interactions between the disturbance and the characteristics of species found in the community or available to colonize, producing both winners and losers of disturbance. When the disturbance is a biological invasion, it has been proposed that other non-native species may be facilitated, producing positive feedbacks that drive an “invasional meltdown.” We investigated this phenomenon in Minnesota, where 100+ years of Cyprinus carpio (common carp) invasion have fundamentally altered the condition of many lakes. Common carp disturb macrophytes through foraging and bioturbation that causes nutrient loading and low water clarity. We evaluated effects of common carp on lake plant communities and tested whether carp were associated with increased occurrence of non-native plant species. We hypothesized that there would be strong shifts in plant community composition associated with carp invasion and that plant species would be differentially sensitive to carp, with non-native plant species more likely to be tolerant. We tested these hypotheses using vegetation, fish, and environmental data collected from 913 lakes over 20 years (1993–2012).
A total of 206 plant taxa were recorded. Plant community composition differed as a function of carp abundance (P = 0.001). There were 86 plant species for which there were sufficient occurrences and geographic overlap with carp to quantify sensitivity to carp while accounting for key environmental covariates. Of these, 25 taxa were classified as sensitive (significant negative relationships with carp), 18 as tolerant (positive relationships), and 43 as intermediate (non-significant, negative relationships). Tolerant taxa were disproportionately non-native (P = 0.002), and included invasive species that are major targets of management: Eurasian watermilfoil, curly-leaf pondweed, purple loosestrife, and narrowleaf cattail. Several native congeners of these species were classified as sensitive, as were species that are threatened, endangered, or extirpated in other Midwestern states, and wildrice, which is of great ecological and cultural importance in the region. Overall, with increasing carp abundance, there were large decreases in species richness and large increases in the proportions of communities comprised by introduced species (P < 0.0001 for both). Patterns were consistent with non-native plant species being more tolerant of, and potentially facilitated by, carp invasion. Carp control may advance management of aquatic invasive plants, restoration of native macrophytes, and conservation of key species.