Ecology of the sea hare Aplysia parvula (Opisthobranchia) in New South Wales, Australia

Abstract

The present study investigates the host range, distribution, abundance, activity and feeding preferences of the sea hare Aplysia parvula on the New South Wales (NSW) central and south coast. Aplysia parvula was found to occur mainly on red algae, especially Delisea pulchra and Laurencia obtusa near Sydney, NSW. The abundance of A. parvula was positively related to the abundance of D. pulchra and L. obtusa and sea hares were absent when survey sites lacked these algae. Aplysia parvula occurred in greater abundance on L. obtusa compared with D. pulchra, although L. obtusa is ephemeral near Sydney. Fluctuations in the abundance of A. parvula on D. pulchra suggest that A. parvula individuals persist for only a few months and are short lived. Aplysia parvula appears to prefer small D. pulchra plants with lower levels of secondary metabolites. The diet of A. parvula was not restricted to host algae, because animals consumed a range of co-occurring red, green and brown seaweeds. Aplysia parvula was nocturnally active on host algae; it grazes and copulates in the canopy of host algae at night, as well as moving between plants. Aplysia parvula may compete with other herbivores (notably Aplysia dactylomela) for the less-abundant L. obtusa resource. Interspecific competition appears less likely on D. pulchra, because few other sea hares were found on this seaweed.