Procambarus clarkii a carrion-feeder: preliminary results on decomposition and colonisation in freshwater

The presence and activity of animals, both vertebrates and invertebrates, on human cadavers can accelerate the processes of decomposition because of dismemberment, tissue laceration and consumption, as well as increase of temperature caused by the animal metabolism. Moreover postmortem animal feeding activity may cause considerable damage to bodies resulting in the modification of wounds, loss of identifying features, and injury or removal of internal organs. Until now, the majority of the published studies and observations concerning the post mortal modifications by animals on carrions and human cadavers have been carried out in terrestrial environments, mainly on exposed bodies. Unlike the situation on land, little information is available in the case of drowning or dead bodies discarded in aquatic environments (e.g., lakes, rivers, sea). However, in the last years several authors tried to bridge this knowledge gap both for freshwater and sea environments. Anyway, aquatic insects and other arthropods can be useful in estimating a Postmortem Submersion Interval (PMSI). The knowledge about the different ‘‘waves’’ of colonization of a submerged body remains incomplete and several differences have been reported case by case. In this study, two experiments were performed in Northern Italy to investigate the effect of crustaceans feeding on carcasses placed in freshwater with a particular attention to Procambarus clarkii (Girard 1982) an alien species illegally introduced into France, Italy and other European countries in 1970-1990. The first experiment started in spring 2012, two carcasses of young pigs (Sus scrofa), dead by natural causes, were positioned into the water. The second experiment started in summer in 2012, for this experiment four carcasses were used. One pig, the control, was placed near the water, the remaining three pigs were placed into the water with different types of protection (nothing, antiaphids net and lobster pot). In the spring experiment, only one specimen of P. clarkii was found at the end of the decomposition process. In the summer experiment, probably due to the increased temperature, P.clarkii individuals were found from the fifth day of the experiment, reaching 69 specimens of this species inside the lobster pot after one month. Our preliminary results indicate that the activity of P. clarkii depend on the water temperature and on the stage of decomposition. This crustacean arrives on a carcass only during the floating decay, skipping the preliminary stages of decomposition.