Migratory waterbirds act as dispersal vectors for a broad variety of organisms that have no or limited means of active dispersal such as plants and invertebrates. In Andalucia, the wintering population of the Lesser Black-Backed gulls (Larus fuscus) has increased greatly over the past 20 years. Larus fuscus individuals move regularly between and within different wetlands and they may play a key role in the dynamics aquatic metacommunites and wetlands across Andalusia by co-dispersing certain species. During the first half of the winter I will quantify and model the co-dispersal effect of gulls in ricefields, giving importance to dispersed weeds that may have an economic impact to the ricefields. The second winter half, I will study and model the co-dispersal connectivity of those gulls between wetlands all around Andalusia focusing in alien species that may be passively transported. I will also focus more in detail in Fuente de Piedra lagoon as an important roosting place of gulls in Andalusia. I will study the behavior of gulls meanwhile they remain in the lagoon and surrondings, and thus, quantify the external nutrient and contamintants transported by gulls.