Filtering out parasites: sand crabs (Lepidopa benedicti) are infected by more parasites than sympatric mole crabs (Emerita benedicti)

Abstract

Two digging decapod crustaceans, the sand crab speciesLepidopa benedictiand the mole crab speciesEmerita benedicti, both live in the swash zone of fine sand beaches. They were examined for two parasites that infect decapod crustaceans in the region, an unidentified nematode previously shown to infectL. benedicti, and cestode tapeworm larvae,Polypocephalussp., previously shown to infect shrimp (Litopenaeus setiferus).Lepidopa benedictiwere almost always infected with both parasite species, whileE. benedictiwere rarely infected with either parasite species. This difference in infection pattern suggests that tapeworms are ingested during sediment feeding inL. benedicti, whichE. benedictiavoid by filter feeding. LargerL. benedictihad morePolypocephalussp. larvae. The thoracic ganglia, which make up the largest proportion of neural tissue, contained the largest numbers ofPolypocephalussp. larvae. Intensity ofPolypocephalussp. infection was not correlated with how longL. benedictiremained above sand in behavioural tests, suggesting thatPolypocephalussp. do not manipulate the sand crabs in a way that facilitates trophic transmission of the parasite.Litopenaeus setiferusmay be a primary host forPolypocephalussp., andL. benedictmay be a secondary, auxiliary host.