Host-parasite interactions of the sardine, Sardina pilchardus (Walbaum, 1792) from the Atlanto-Iberian Waters

The European sardine, Sardina pilchardus (Walbaum, 1792) is one of the most abundant small pelagic clupeids and holds significant commercial value. Adult specimens were obtained along the Western and Southern Iberia, covering three ICES sub-divisions: 9aCN-Northerwestern Iberia, 9aCS-Southern Iberia and 9aS-South Iberia. A parasitological survey was carried out to characterize sardine parasite fauna and to assess its potential as a proxy for the spatial distribution of free-living parasite biodiversity and sardine trophic interactions, based on parasite richness and diversity. Parasites were analysed in different host organs and tissues. Fourteen parasite taxa were identified, which include Apicomplexa, Myxozoa, Monogenea, Digenea, Cestoda, Nematoda and Acanthocephala. Species diversity was higher in the Digenea group with a total of 2 116 specimens recorded. The Monogenea, Mazocraes alosae; the Cestoda, Scolex pleuronectis; the Acanthocephala, Rhadinorhynchus sp. and the Nematoda, Anisakis sp. and Hystherothylacium sp. larvae were also identified. This is the first study to investigate the relationship between parasite assemblages and diet composition in sardines from the Atlanto-Iberian coast. The finding highlight the potential of parasite fauna as indicator of food webs structure, free living parasite biodiversity and ecosystem stress, providing insights into differences observed among ICES sub-divisions. Both qualitative and quantitative variations in sardines' parasite comunities from the three ICES sub-divisions are in line with the differences observed in their prey composition, reflecting fine-scale trophic interactions linking parasites with intermediate and paratenic hosts present in the sardine diet.