The red swamp crayfish, P. clarkii, is one of the most ecologically damaging aquatic species. A native of Louisiana, this freshwater crustacean has invaded Mediterranean ecosystems in 5 of the 7 continents, imposing detrimental effects on each.
Scott Valentine of Duke University has proposed a study to determine the mechanisms by which P. clarkii reduces biodiversity in invaded ecosystems. Valentine hopes to find major differences in the food preferences of the native and invasive crawfish. He is confident that he will find sufficient support since many faculty members from the University of Florence and other universities throughout southern Europe have expressed interest and dedication to the study of P. clarkii.
Valentine believes the study will take approximately 15-36 months to complete. Field collections in two northern Italian streams, one dominated by P. clarkii and the other by A. italicus, will take about a year and may enlist supplementary assistance from citizen scientists. The bulk of the work, however, will take place in the lab as scientists analyze the stomach contents of the different species collected to determine the contrasting diets of the native and invasive crayfish species. Organic material found in the stomachs of each will likewise be scrutinized to ascertain the major ecosystem differences resulting from the P. clarkii invasion.
P. clarkii is a keystone species which further complicates the establishment of effective removal methods. This invasive species fills the niche originally held by the native crawfish species in each habitat but causes all sorts of problems because it is not a perfect match. “Ideally we would want to remove all P. clarkii and replace them with the native A. italicus species, but it is not that simple,” reports Valentine. The balance previously maintained in this ecosystem cannot be achieved because of the environmental alterations that have begun because of the P. clarkii introduction. On the whole, Valentine is referring to the “crawfish plague.” One of the most unfortunate consequences of P. clarkii invasion is its simultaneous transportation of the fungus A. astaci. When this fungus is brought in to foreign ecosystems that haven’t been acclimated to it, the local crawfish die.
“What we really are hoping to achieve is the reduced spread of invasive species, specifically the red swamp crayfish. This is a slippery slope, however, because native species are having difficulties reestablishing themselves due to the fungi transported via the invasive crayfish,” says Valentine. In addition to the stress placed on the environment by P. clarkii who dominate the native population and upset the natural balance of resource chains, the fungus serves as a major impediment. In order to return to the initial conditions before the invaders scientists would have to do more than just eliminate P. clarkii entirely, since the fungus spreads to the native species which in turn either die or subsequently serve as carriers for many years. Complete extermination of both the native and non-native invasive species as well as eradication of the fungi would all need to occur for a return to normalcy.
Biodiversity loss is a major factor contributing to the problem with this invasive species. Specifically, the loss of biodiversity after the invasion of P. clarkii caused a decrease in the freshwater volume of detritus, small fishes, and benthic organisms (all part of the P. clarkii diet), all of which contributed to a decrease in the water quality. P. clarkii burrow in the sides of streams where rice plantations are located and they caused a widespread decline in various countries’ rice production. Humans are inherently linked to the environment and thus also bear the repercussions of this invasive species.
In sum, Valentine’s study will enable scientists to learn how the P. clarkii changes an ecosystem by examining its food sources and the overall mechanisms by which it invades and dominates foreign habitats. More effective control methods can eventually be developed to end the invasion and continued eco-trauma delivered by the red swamp crayfish.