White Amur Grass carp are known to eat aquatic plants, which is beneficial for fish farms or ponds with low vegetation. However, grass carp have been reported to eat trees, shrubs, and even corn in the USA. This is problematic as it may result in the overgrowth of vegetation, eventually leading to the starvation of other fish and plants. Anecdotal reports have stated that grass carp can even eat duckweed and water hyacinth. Grass carp certainly can eat duckweed and water hyacinth. However, grass carp do not actually prefer these plants when given a choice of foods with similar size and nutrient profiles.
The reason why grass carp may be considered a threat in certain ecosystems is that they can out-compete other herbivorous species that also consume plants. If grass carp are in an area with many small to medium-sized predators that feed on them, grass carp will not do well in that environment because they can be preyed upon. However, when there are few or no predators around, the same applies to all other herbivores present. In that case, grass carp can eat all the plants and then leave only the large predators behind that cannot be eaten by other fish. Once this happens, all of the smaller herbivores can be removed from the ecosystem.
This means that if grass carp are introduced into an environment without any predators (for example a freshwater pond), they will eventually become the only species of large herbivore left as all the other fish become too small to prey on. In this case, grass carp will compete with each other for food, and eventually, the population will be forced into a decline due to competition or starvation.
Adult white amur do not have any predators because they are too large and difficult to catch. This means that death by predation is quite rare in grass carp as well since they usually will be able to escape from a predator without harm. In addition, many plants protect grass carp as well. For example, grass carp can protect themselves by hiding in tall plants such as hydrilla, wild rice, and eelgrass.
Another reason why grass carp are considered a threat is that they can damage wetland habitats. The root systems of aquatic plants provide habitat for many invertebrates and other fish species. Thus, the loss of vegetation leads to a loss in invertebrates and animals that feed on them. In addition, aquatic plants protect ponds from erosion by stabilizing sediments at the bottom. Thus, when vegetation is removed from a pond or lake bottom, erosion increases, and sedimentation can become a problem.