Impacts of a not-indigenous invasive species (Procambarus clarkii Girard, 1852) on the ecological attributes of a managed saltmarsh (Stagno di Molentargius, Sardinia)

The red-swamp crayfish Procambarus clarkii, native to NE Mexico and S USA, is among the most successful and invasive alien species that entered European freshwaters during the last 30 years. This species has expanded very rapidly thanks to early sexual maturity, rapid growth, large numbers of offspring, short life spans, high tolerance to drought and high temperatures. The Molentargius-Saline Regional Natural Park (Sardinia, Italy) is a managed saltmarsh, where, in 2004 a filtering ecosystem (ESF) has been established by removing all the existing vegetation and transplanting the macrophyte Phragmites australis, which remove undesirable substances by direct assimilation and provide a favorable habitat for the bacteria that transform pollutants. Since 2004, the number of plant taxa increased at an annual rate of ca. 14%, reaching in 2016 a total of 275 taxonomic units, of which 10 of conservation concern and 32 aliens. We investigated: 1) P. clarkii abundance in the ESF and its drainage channel, using baited traps; 2) sedimentary organic matter (OM) quantity and biochemical composition, along with the vegetation attributes and biodiversity of three invaded portions of the basin characterized by high, intermediate and low levels of shrimp abundance (1.5, 1 and 0 catch ind. day-1 respectively). A total of 129 shrimps were sampled in 329 stations (LCmed=40.79±6.98 mm; PTmed=15.67±7.84 g), with the highest abundance occurring in emerging soft soils. Highest shrimp abundance was associated with the lowest OM contents and a decreasing proportion of proteins and carbohydrates, suggesting that P. clarkii can alter significantly the availability of food for other benthic consumers. Phragmites australis, the dominant plant, creates a quasi-continuous strip around the sub-basins. We report that the thickness of the plant strip is not related to P. clarkii density, concluding that the emerged vegetation is not a main factor regulating the presence and abundance of P. clarkii in the ESF or vice-versa. This study was supported by the Fondazione di Sardegna (year 2016) and Regione Sardegna (LR 7/2007) for the project Impact of Invasive Alien Species on Sardinian ecosystems and by the Fondazione con il Sud for the project Nr. 2015-AMB-0065