Estresse hidrol?gico como fator limitante para a invas?o de Limnoperna fortunei (Dunker,1857) no Alto Rio Paran? (Brasil).

Limnoperna fortunei (Dunker, 1857), ? um molusco asi?tico que chegou na Am?rica do Sul em 1991. Desde 2004 verificamos que o avan?o da esp?cie no Baixo Rio Parana?ba, afluente do Alto Rio Paran?, ? lento quando comparado com a velocidade m?dia de 240 km/ano nos cursos m?dio e baixo do rio Paran?. Objetivo: O objetivo deste trabalho ? entender quais s?o os fatores limitantes da dispers?o de L. fortunei neste trecho do rio Parana?ba. M?todos: Sua ocorr?ncia e dispers?o foram amostradas doze vezes entre mar?o de 2006 e novembro de 2007 no rio Parana?ba, incluindo o reservat?rio da usina hidrel?trica de S?o Sim?o. Resultados: Mexilh?es adultos foram encontrados aderidos aos cascos dos barcos que circulam neste trecho da hidrovia Paran?-Tiet? e em embarca??es atracadas nos portos de empresas exportadoras de gr?os localizadas em S?o Sim?o (GO). No entanto, larvas e adultos n?o foram encontrados nas proximidades dos portos nem a montante dos mesmos, no reservat?rio da hidrel?trica de S?o Sim?o. O pH, a concentra??o de c?lcio e os valores m?dios de oxig?nio dissolvido s?o semelhantes entre ambientes l?ticos e o reservat?rio: as concentra??es m?dias de oxig?nio est?o pr?ximas de 7 mg.L?1, o pH m?dio est? em torno de 7, os valores m?dios de Ca total variam entre 4 e 6 mg.L?1 e os n?veis de clorofila a n?o s?o restritivos para esta esp?cie de mexilh?o. Conclus?o: As vari?veis f?sico-qu?micas da ?gua indicam que os habitats s?o adequados para o estabelecimento da esp?cie. Al?m de uma baixa press?o de prop?gulos, este trabalho prop?e algumas vari?veis hidrol?gicas, tais como, a energia dos trechos fluviais e mudan?as da vaz?o a jusante da barragem, como barreiras para o estabelecimento da esp?cie, uma vez que estes aspectos podem desfavorecer a fixa??o e sobreviv?ncia das larvas e diminuir o recrutamento.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 Parana?ba River, a tributary of the Upper Paran? River, is slow when compared to the average speed of 240 km/year in the Paran? 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 Parana?ba River. Methods: Its occurrence and dispersion were sampled twelve times between March 2006 and November 2007 in the Parana?ba 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 Paran?-Tiet? 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