Dispersal of two freshwater invasive macroinvertebrates, Procambarus clarkii and Physella acuta, by off-road vehicles

Abstract

The red swamp crayfish (Procambarus clarkii) and the bladder snail (Physella acuta) are two invasive aquatic macroinvertebrate species with worldwide distribution that are plagues in rice fields. The purpose of this study was to investigate the possibility of accidental human dispersal of these two species by off-road vehicles. An experimental approach was used owing to the difficulty of obtaining field data on low-probability events such as passive dispersal. Experiments were performed testing the probability of attachment of both organisms to mudguards of off-road vehicles as well as successful transport and release into the receiver water body. Recently-hatched P. clarkii and all P. acuta sizes available in the field were used. Results showed that P. clarkii and P. acuta can be transported in mud adhering to an off-road vehicle. No differences were found in the proportions of adhered organisms between species or for each species at the different densities used because of low overall retrieval. For P. acuta, the attachment probability varied between 0.5% both for 50 and 200 individuals m-2 and 1% for 100 ind. m-2. For P. clarkii, no individuals adhered at 50 ind. m-2, but the probabilities were 1% and 1.5% for 100 and 200 ind. m-2, respectively. A transport-survival experiment showed a mean survival distance of 83.2 km for P. clarkii and 92.2 km for P. acuta under dry conditions. Rain or wet conditions severely reduced successful transport. The proportion of organisms falling into a receiving water body increased with the vehicle's speed while crossing the water. Although the results demonstrated a low probability of occurrence of attachment, they also showed that, if attachment occurs, aquatic organisms have a high chance to be released successfully in a suitable environment after long-distance transport by vehicle.