Diatomáceas sobre Limnoperna fortunei (Dunker), molusco introduzido no Lago Guaíba, Sul do Brasil

Abstract

The taxonomic composition of diatoms present on the mollusk Limnoperna fortunei (golden mussel), introduced into Guaíba Lake through ballast water, from ships coming from Argentina, was analyzed with the intention of identifying and evaluating the occurrence of the species in relation to habitat and origin. Mollusks were obtained from a floating wooden platform and on floats situated in the northern region of Guaíba Lake, during the period of August to November 2005. The diatoms were scraped from the shells, analysed under microscope and were oxidized for identification. Results have shown that the molluskan shell may be a favorable habitat for diatom, considering the species richness. Diatom association did not demonstrate to be restricted this habitat, since the most frequent species: Cocconeis fluviatilis Wall., C. placentula Ehr. var. lineata (Ehr.) Heurck, Encyonema silesiacum (Bleisch) Mann, Eunotia pseudosudetica Metz., Lange-Bert. & Garcia-Rodr., Gomphonema parvulum (Kütz.) Kütz., Hydrosera whampoensis (Schw.) Deby, Luticola goeppertiana (Bleisch) Mann, Melosira varians Ag., Navicula symmetrica Patr., Nitzschia palea (Kütz.) Smith, Pinnularia acrosphaeria Smith, Planothidium frequentissimum (Lange-Bert.) Round & Bukh., Pleurosira laevis (Her.) Comp. and Ulnaria ulna (Nitzsch) Comp. were found on rocky substrata and in the plankton of the Guaíba Lake hydrographic basin. Therefore, Eunotia pseudosudetica, Luticola dapalis (Freng.) Mann and Gomphonema mexicanum Grun. are taxa only reported, until now, for the Rio de la Plata, Argentina and their occurrences in Guaíba Lake support the hypothesis of a recent introduction of these species through ballast water as L. fortunei.