Larval digenean preferences in two sympatric snail species at differing tidal levels off the Atlantic coast of Patagonia

Abstract

AbstractLarval stages of the trematodesMaritrema madrynenseand Hemiuroidea fam. gen. et sp. differentially parasitizedSiphonaria lessoniiandS. lateralis, two sympatric pulmonate snail species on the rocky intertidal shore at Puerto Deseado, south-western Atlantic coast of Patagonia, Argentina. Snail specimens were collected at two sampling sites with contrasting physical–chemical characteristics. One site, in the upper intertidal, was exposed to sewage from fish-processing plants, greater hydrodynamic forcing and desiccation, a wider temperature range, longer exposure to ultraviolet radiation and higher abundance of birds. The second site, in the lower intertidal, was generally characterized by less stressful environmental conditions. At both sites,S. lateralisshowed a markedly higher density thanS. lessonii(55.13 vs. 5.87 snails/m2, respectively). Despite this, the prevalence of both digeneans was higher inS. lessonii(17.37% and 3.52% forM. madrynenseand Hemiuroidea, respectively) than inS. lateralis(0.09% and 0% forM. madrynenseand Hemiuroidea, respectively). This study demonstrates high parasite specificity for the host. Low densities ofS. lessoniiare attributed to castration of parasitized hosts and reduction of their physiological condition. The prevalence and intensity of infection of both digenean parasites were higher at the more stressful, upper intertidal site, thus suggesting that a higher abundance of birds and exposure to sewage pollution may promote the transmission of trematodes.