A commensal relationship between the scyphozoan medusae Catostylus mosaicus and the copepod Paramacrochiron maximum

The copepod Paramacrochiron maximum was found in high numbers (up to 5,675 copepods/medusa) on the oral arms of the scyphozoan Catostylus mosaicus. This association was considered to be commensalism for the following reasons: P. maximum (Lichomolgidae) was abundant on the medusae (approximately 805 copepods/kg of medusae) and very rare in the water column (approximately 5.99×10-4 copepods/kg of water); copepodites and adults of the symbiont were present on the host; the copepods were on the medusae both day and night, at different times (nine occasions between March 1999 and May 2000) and different locations (Botany Bay and Lake Illawarra, NSW, Australia). Over 40 taxa of plankton were found on the oral arms of C. mosaicus (including protists, cnidarians, polychaetes, molluscs, a wide range of holoplanktonic and meroplanktonic crustaceans, chaetognaths and fish eggs). These taxa were abundant in the water column and we concluded that they were prey. Symbiotic amphipods and carangid fishes were found with medusae. We conclude that there is a symbiotic association between P. maximum and C. mosaicus and care should be taken not to confound these copepods with the prey of C. mosaicus. Poecilostomid copepods are well known for consuming mucus and feeding is likely to be a major reason for the association