Structural damage caused by the invasive crayfish Procambarus clarkii (Girard, 1852) in rice fields of the Iberian Peninsula: a study case

The red swamp crayfish (Procambarus clarkii) is considered one of the most invasive species for aquatic ecosystems. Since its introduction in Spain in 1973, it has spread over different wetlands throughout Western Europe, having rapidly adapted to lakes, ponds and coastal marshes. Among the invaded ecosystems, rice-growing areas have been largely affected by crayfish habits, mainly due to their digging behaviour. In pursuit of this, we attempted to draw some patterns about the dynamics of the red swamp crayfish population inhabiting the Ebro Delta Natural Park (NE Spain) - one of the main rice-producing areas within the Mediterranean region - in relation to the structural damage caused to draining structures. More specifically, we aimed at establishing links between the local densities of crayfish, the abundance of burrows they use to shelter, and the intensity of damage involved by crayfish digging activity. For this purpose, two approaches relating crayfish density data with abundances of burrows, complemented with in-situ observations of structural damage, were designed. Preliminary results indicated that crayfish density and the number of active burrows were positively related, with higher values implying severe damage to draining structures. However, intense digging activity periods did not directly relate to crayfish density, since other factors were also involved. The information obtained could be useful in planning future surveys in which sound details on digging behaviour and, consequently, the structural damage entailed, could be profitably assessed.