Jacopo Cerri , Ernesto Azzurro

Aquatic Invasive species (AIS) are a growing driver of change across marine and freshwater ecosystems but spatially-explicit information is seldom available for supporting management actions and decision making. Here we conceived and tested a new participatory method to map the distribution of three invasive species (Callinectes sapidus, Procambarus clarkii and Oreochromis niloticus) in the coastal lagoon of Lesina (Italy). Local fishers were asked to draw the distribution of each species on pre-printed maps, indicating districts of the lagoon characterized by different abundance levels. Then, maps were converted to a lattice grid and a Bayesian hierarchical Generalized Additive Modeling was adopted to model species distribution in the lagoon, calculating the coefficient of variation for model fitted values to map fishers agreement about the distribution of each species.
The spatial gradient in the abundance of the three species in the lagoon aligned with their ecological requirements. C. sapidus was abundant throughout the whole lagoon, peaking in correspondence of saltmarsh vegetation, while P. clarkii and O. niloticus, were much less abundant and remained distributed near to freshwater inputs. Experts agreed about the spatial distribution of C. sapidus in the lagoon, with a median coefficient of variation in model fitted values of 3.9%. On the other hand, the coefficient of variation was higher for P.clarkii (19.9%) O. niloticus (18.4%), indicating a higher level of uncertainty about their estimated distribution.
With this example, we provided new metrics to evaluate the quality of LEK-based participatory mapping in terms of agreement and consistency among experts. The resulting information provides new insights for spatially informed management across aquatic realms in relation to the increasing ecological and socio-economical pressures posed by biological invaders.