Larval stages of the golden mussel Limnoperna fortunei (Dunker) (Bivalvia, Mytilidae) in Guaiba Basin, Rio Grande do Sul State, Brazil.

摘要

Since the end of 1998 a small invasive bivalve, the golden mussel Limnoperna fortunei (Dunker, 1857), originating from Southeast Asia, is present in Southern Brazil. It was probably brought not intentionally in ballast water to the Guaiba Basin in Rio Grande do Sul State. In this environment, the golden mussel is causing macrofouling very rapidly with grate financial loss and damages to the native fauna and flora. Quali-quantitative samplings twice a month were performed during one year in the Guaiba lake, at Veludo Beach (30 degrees 12'35"S, 51 degrees 11'68"W) southward of the municipality of Porto Alegre. Each time, 30 litters of water were filtered through plankton net with a mash opening of 36 mm. The different larval stages with the length parameters were briefly described. Different stages were recognized: five without valves and four valved. The first one recognized as a ciliated stage develops into the trocophora (length from 80 pm to 125 pm) with four distinct stages. The valved stages include: the "D" - shaped (length 120 mu m to 150 mu m), the straight-hinged veliger (length 150 mu m to 190 mu m), umbonated-veliger (length 190 mu m to 220 mu m) and pediveliger (length 220 mu m to 250 mu m). When pos-larvae or plantigrades (length about 300 mu m), they secrete the byssus thread that permit fixation on the subtract. Larvae were present during all the samplings with strong October-December peaks.