The symbiotic relationship between Lychnorhiza lucerna (Scyphozoa, Rhizostomeae) and Libinia spinosa (Decapoda, Epialtidae) in the Rio de la Plata (Argentina-Uruguay)

Herein, we characterize a symbiotic relationship between the scyphomedusa Lychnorhiza lucerna and the decapod crustacean Libinia spinosa in Rio de la Plata, South America. Of 843 specimens of L. lucerna examined during the study, 69 (8.2 %) hosted L. spinosa within subgenital spaces. The broad spatial and temporal scale of the study, together with the large number of observations made, confirm an association between the two species. Medusae having crab associates were mature and larger than those lacking such symbionts. Adult crabs of both sexes, as well as juveniles and soft-shell individuals, were found as associates of medusae. Analysis of crab stomach contents revealed the presence of nematocysts and copepod remains. Our results suggest that medusae provide protection and possibly access to food for crabs. Benefits related to transportation were not clear and need further evaluation. Crabs of L. spinosa may acquire their scyphozoan symbionts either as larvae planktonic stages or as adult crabs attaching to jellyfish when aggregating close to bottom.