Hydrological stress as a limiting factor of the invasion of Limnoperna fortunei (Dunker, 1857) in the Upper Paraná River (Brazil) Estresse hidrológico como fator limitante para a invas o de Limnoperna fortunei (Dunker,1857) no Alto Rio Paraná (Brasil)

Limnoperna fortunei (Dunker, 1857), is an asiatic mussel that arrived in South America in 1991. Since 2004, we have noticed that the advance of this species in the lower Paranaíba River, a tributary of the Upper Paraná River, is slow when compared to the average speed of 240 km/year in the Paraná River (middle and lower course). AIM: The goal of this work is to understand what factors are limiting the spread of L. fortunei in this stretch of the Paranaíba River. METHODS: Its occurrence and dispersion were sampled twelve times between March 2006 and November 2007 in the Paranaíba River, including the S o Sim o hydroelectric reservoir. Physicochemical characteristics of the water were analysed, and a Stream Length-Gradient Index calculated for the study area. RESULTS: Adult mussels were easily found attached to the hulls of barges that travel on this stretch of the Paraná-Tietê waterway and on vessels that were docked in the harbours of grain exporters located in S o Sim o (GO). However, no larvae or adults were found near the harbours or upstream from them at the S o Sim o hydroelectric reservoir. The pH and concentration of calcium and dissolved oxygen values among lotic habitats and the reservoir were similar: DO values were close to 7 mg.L-1, the average pH was near 7, average values of total Ca ranged between 4 and 6 mg.L-1 and the chlorophyll-a levels were not restrictive to the mussel. CONCLUSION: Physical and chemical water parameters show that habitats were suitable for establishment of the mussel. In addition to a low pressure of propagules, this paper proposes some hydrological variables, such as the energy of the fluvial stretches, expressed by the Stream Length-Gradient Index and changes in flow downstream of the dam as barriers to the establishment of the species, discouraging larval settlement, and decreasing survival and recruitment. Limnoperna fortunei (Dunker, 1857), é um molusco asiático que chegou na América do Sul em 1991. Desde 2004 verificamos que o avan o da espécie no Baixo Rio Paranaíba, afluente do Alto Rio Paraná, é lento quando comparado com a velocidade média de 240 km/ano nos cursos médio e baixo do rio Paraná. OBJETIVO: O objetivo deste trabalho é entender quais s o os fatores limitantes da dispers o de L. fortunei neste trecho do rio Paranaíba. MéTODOS: Sua ocorrência e dispers o foram amostradas doze vezes entre mar o de 2006 e novembro de 2007 no rio Paranaíba, incluindo o reservatório da usina hidrelétrica de S o Sim o. RESULTADOS: Mexilh es adultos foram encontrados aderidos aos cascos dos barcos que circulam neste trec