Outbreak of a neurotoxic side-gilled sea slug (Pleurobranchaea sp.) in Argentinian coasts

Abstract

Since 2009 we have been registering the outbreak of an unknown side-gilled sea slug of the genus Pleurobranchaea in coastal waters of Argentina, southwestern Atlantic Ocean. Examination of both external macroscopic features and internal structures via electron microscopy did not allow us to conclusively identify the species. Nevertheless, since Argentinian specimens closely resemble Pleurobranchaea maculata (a species native from Australia and New Zealand known to contain a potent neurotoxin) we performed a bioassay in our specimens, which was positive for neurotoxins. The presence of this pleurobranch in Argentinian waters is of concern beyond the ecological effects of the outbreak of a marine predator and requires urgent attention. This work provides a guide to distinguish between this unidentified species and the sympatric cryptogenic Pleurobranchaea inconspicua, based on features that are readily observable in fresh and preserved specimens. We discuss the potential effects of this outbreak on local communities.