Authors

S Correia¹; L Magalhães¹; X de Montaudouin²; R Freitas¹;  ¹ University of Aveiro, Portugal;  ² University of Bordeaux, France

Discussion

The edible cockle, Cerastoderma edule, is a widely distributed bivalve along the European aquatic systems. This species displays an important ecological and socio-economic role, being the most exploited bivalve in Portugal. Cockles act as first and/or second intermediate host for several trematode species. Trematodes are the most abundant and common macroparasites in coastal waters, displaying a complex life cycle alternating, generally, between three hosts. Trematodes, as parasites in general, present a key structuring role in communities, imposing adverse impacts on the host population dynamics. Therefore, it is of upmost importance to recognize the diversity and abundance of the species infecting cockles. In this way, the present study aimed to i) provide the first survey of trematodes infecting C. edule in several Portuguese aquatic systems and ii) correlate the infection level to environmental parameters (water temperature and salinity, sediment median grain size and organic matter, tidal regime and coastal system type).

Cockles monitoring was conducted from July to October 2016 in six Portuguese aquatic systems. A total of 10 species of trematodes were observed infecting cockles as first and second intermediate host. Despite the main results showed a heterogeneous trematode community among aquatic systems, two groups were identified, differing in terms of species richness and trematode mean abundance. The first group, including lower abundance values, was composed by the only subtidal area and by a lagoon characterized by low water exchanges. The second group, mainly characterized by a higher abundance of trematodes, highly correlated to the prevalence of the trematode Parvatrema minutum, was composed by lagoons and estuaries with significant water exchanges. These results emphasized the importance of biotic and abiotic habitat characteristics in determining the trematode distribution with more oceanic influenced areas, characterized by lower water temperature variation and higher hydrodynamic features presenting higher infection level. On the other hand, more sheltered areas, with lower water exchanges, despite the higher water temperatures reached, were characterized by lower abundance of trematodes.

In conclusion, this study suggested that one of the most limiting factor for trematode infection in C. edule populations was the more or less sheltered status of the habitats. Moreover, this work highlighted the ubiquity of trematode parasites in the different lagoons and argued in the necessity to incorporate them in ecological studies, in particular due to their potential negative impact on host populations.