Population dynamic of two digenean species parasitizing the grass shrimp Palaemonetes argentinus Nobili 1901 (Decapoda: Palaemonidae) in a lentic environment from Argentina.

The microphallids Microphallus szidati and Levinseniella cruzi parasitized at least three crustacean species as second intermediate host in Mar Chiquita coastal lagoon: the crabs Neohelice granulata and Cyrtograpsus angulatus and the grass shrimp Palaemonetes argentinus. Palaemonetes argentinus acts as host for both metacercariae in brackish and freshwater environments; however the seasonal variations of these digeneans in freshwater habitats remain unexplored. The aim of the present study was to analyze the seasonal dynamic of the larval digenean populations parasitizing P. argentinus in a lentic environment. From the total sample of 600 P. argentinus collected seasonally, 28.370 and 194 metacercariae of M. szidati and L. cruzi, respectively, were recovered. Microphallus szidati was characterized by high prevalence, 100% in all seasons. In contrast, L. cruzi presented low prevalence values, which increased towards summer. The two species of digeneans exhibit seasonal fluctuations in intensity of infection, which was related to host size. Temporal variation of larval digenean assemblage in the crustacean host is probably associated with the presence of the other hosts included in their life cycles. The high values of prevalence found for M. szidati in Nahuel Rucá lagoon suggest that P. argentinus could favor the contact between the larval digenean and the definitive hosts, establishing the presence of M. szidati also in freshwater environments and, thus, increasing the presence of the parasite in different areas of Mar Chiquita coastal lagoon.