Qualitative and quantitative data of the larval stages of 30 helminth species infecting fish and shellfish in the Santa Gilla lagoon (southern Sardinia, western Mediterranean Sea) were collected and analysed to determine their usefulness as biological and ecological indicators. Parasitological data were collected from 2001 to 2011 from 12 fish species, from the families Anguillidae, Atherinidae, Cyprinodontidae, Gobiidae, Moronidae, Mugilidae, Soleidae and Sparidae and from bivalve molluscs of the families Cardiidae, Mytilidae and Veneridae. Digenean metacercariae dominated the larval parasitofauna; nevertheless, the most abundant parasite species was a nematode, i.e. the third-stage larvae of the anisakid Contracaecum rudolphii. Based on their life cycle, the species detected were divided into autogenic or allogenic parasites, which have fishes and birds/mammals as their definitive hosts, respectively. Data on the prevalence, intensity and abundance of infections and the parasitic diversity in each host species were combined with previous knowledge on the life history of the parasites detected, to build a model food web based on the different trophic relations, especially predator–prey interactions between hosts marked by the transmission of parasites. The results will contribute to the knowledge of species diversity and to the evaluation of general environmental changes occurring in brackish Mediterranean ecosystems. In combination with other analytic tools in a multidisciplinary approach, this will enable us to better understand the functioning of other Mediterranean brackish waters that are comparable to the Santa Gilla lagoon.
