Dynamics of the Upogebia pusilla–Gyge branchialis marine host–parasite system

Abstract

The influence of burrowing invertebrates on the functioning of soft-bottom ecosystems is tightly dependent on their physiological state, which may itself be strongly affected by parasite infestation. However, the dynamics, prevalence and physiological consequences of parasitism remain poorly known in many species, such as sediment-dwelling crustaceans. During the present study, we investigated the effects of the ectoparasite (bopyrid) isopod Gyge branchialis on the fitness of the gebiidean mud shrimp Upogebia pusilla. A spatial survey conducted in June 2013 at 10 stations scattered across intertidal seagrass meadows of Arcachon Bay (44°40′N, 1°10′W) showed that on average 16 % of mud shrimp were infested by G. branchialis. Moreover, a temporal survey carried out at one of these stations over the year 2014 revealed that prevalence remained relatively high throughout the year, ranging from 10 to 33 %. This interaction has various physiological consequences for U. pusilla. In particular, infested mud shrimp consistently exhibited a significant deficit in total length and individual dry weight as compared with non-infested specimens. Moreover, 89 % of infested males were feminized (i.e., developed female secondary sexual characters), whereas infested females were never ovigerous. Our results demonstrate that G. branchialis strongly impair U. pusilla fitness including its ability to reproduce. Accordingly, through their (1) potential impact on mud shrimp abundances and (2) alteration of their physiological state, high bopyrid infestation could profoundly alter the bioturbation activity of mud shrimp populations and overall their influence on the functioning of soft-bottom ecosystems in Arcachon Bay.