On the occurrence and ecology of Glaucus atlanticus Forster, 1777 (Mollusca: Nudibranchia) along the Southwestern Atlantic coast.

Unlike the majority of the nudibranchs, Glaucidae lives adrift at the sea surface within Tropical and Subtropical ocean basins, feeding on cnidarians or using them to attach their egg strings as a reproductive strategy. The latitudinal distribution of Glaucus atlanticus throughout the Brazilian Province is influenced by the Brazil current and, in its austral limit, by seasonal shifts in the Subtropical Convergence Zone (especially under the influence of ENSO El Niño events). Once over the shelf, seasonal wind patterns and meteorological events can force a passive displacement of the species towards the shore. Such onshore displacements may result on strandings of Glaucus spp. and other pleustonic species of the "blue plankton" community, like already reported worldwide and recently at the Southern Brazilian / Uruguayan coasts. Although fascinating, Glaucus spp. should be considered harmful to humans and people should thus avoid direct contact; if this accidentally occurs, short-term treatments can be implemented besides looking for medical attention. The current geographical distribution of Glaucus atlanticus over the Brazilian coast reveals some inaccuracy and gaps; the present study not only revises the ecology of this species but also evidences the occurrence of summer strandings and its austral distribution into subtropical shores.