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.
Highlights
Interspecific differentiation among side-gilled sea slugs of genus Pleurobranchaea is problematic because of their high morphological similarity
For observations of the external morphology, individuals were fixed in formalin for 48 h and transferred to 70% ethanol for long-term storage in the collection of the Museo Argentino de Ciencias Naturales Bernardino Rivadavia, Buenos Aires, Argentina, catalogue number MACN-In: 39571
Specimens were first found within the Mar del Plata Port (38°04S, 57°53W), but recently NEF, on board of the R/V Puerto Deseado, has added new records that extend their distribution up to 60 m depth within the Buenos Aires coastal area
Summary
Interspecific differentiation among side-gilled sea slugs of genus Pleurobranchaea is problematic because of their high morphological similarity. All members of Pleurobranchaea are medium to large sea slugs, pale grey to brownish in colour. High levels of tetrodotoxin (TTX) were found in adults, eggs and early larval stages of Pleurobranchaea maculata (McNabb et al 2010), though concentration varies greatly across individuals, seasons and populations (Wood et al 2012). TTX is an extremely potent neurotoxin that inhibits the propagation of action potentials in muscle and nerve cells; the ingestion of just 1–2 mg of TTX can cause death in adult humans (Noguchi & Arakawa 2008)
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