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

Raphael M Pinotti,Erik Muxagata,Fabio C Bom

doi:10.1590/0001-3765201920180154

Raphael M Pinotti, Erik Muxagata + Show 1 more

Open Access

https://doi.org/10.1590/0001-3765201920180154

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Abstract

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.

Highlights

Nudibranchs form the most diverse order of opistobranch gastropods and are recognized by the soft and elongated shell-less body, with the majority of the species within this order being epibenthic crawlers
Coastal reefs and rocky shores can contribute for the occurrence of relatively high diversity of bottom-dwelling nudibranchs along the Tropical Southwest Atlantic - within the Southern Brazilian Bight - and a decreasing diversity towards the Subtropical Southern Brazilian Shelf (García et al 2006). Such lower diversity may be attributed to morphology changes on the coastal plain - from the Rio Grande do Sul state (≈ 29o S) to the northeastern Uruguayan coast (≈ 34o S) - in which rocky shores are replaced by sandy shores, environments recognized as unfavorable for benthic nudibranch species (Franz 1970)
A different story can be told to those species adapted to the pelagic realm: only few nudibranchs are truly holoplanktonic, displaying complete life cycles in the water column, like the pleustonic species of the family Glaucidae that are usually found floating at the sea surface (Lalli and Gilmer 1989) and not influenced by bottom composition and its morphology

Summary

Introduction

Nudibranchs (commonly known as sea slugs) form the most diverse order of opistobranch gastropods and are recognized by the soft and elongated shell-less body, with the majority of the species within this order being epibenthic crawlers. Such cold-water barrier can play a significant role for the lowest diversity of opistobranchs within the Southern Brazilian Shelf (García et al 2006) due to its proximity to the Subtropical Convergence Zone (Garcia 1997)

Results

Conclusion