Environmental factors influencing the occurrence of alien mollusks in semi-arid reservoirs

portuguesO objetivo deste estudo foi avaliar quais variaveis ambientais tem maior influencia na ocorrencia de moluscos exoticos em reservatorios do semiarido em periodo de seca. Este estudo foi realizado nos reservatorios de Argemiro de Figueiredo, Epitacio Pessoa e Pocoes, bacia hidrografica do Rio Paraiba / Brasil, nos meses de julho e outubro de 2015. Em cada reservatorio, as amostragens foram realizadas em tres regioes: 1) perto da entrada do principal afluente; 2) a secao do meio reservatorio; e, 3) perto da barragem. Para cada regiao foram estabelecidos tres locais de amostragem. Os parâmetros fisicos e quimicos da agua foram medidos, bem como a composicao granulometrica do sedimento foi estimada em cada local. Foram identificados 8635 individuos bentonicos, sendo 6569 moluscos exoticos. No Argemiro de Figueiredo os moluscos exoticos representam 90 %, Epitacio Pessoa 63 % e Pocoes 35 % da comunidade bentonica. Melanoides tuberculata (6283 individuos) foi a especie mais abundante, seguida de Corbicula largillierti (286 individuos). Diferencas significativas foram observadas para a abundância de especies exoticas entre os reservatorios (p=0.0001) e entre os periodos de amostragem (p=0.0001), nao sendo observado o mesmo para as regioes (p=0.937). Para os parâmetros ambientais, houve diferencas significativas entre os reservatorios (p=0.0001), mas nao para as regioes (p=0.7428) e os periodos de amostragem (p=0.346). O modelo Best (R2=0.61) selecionou cinco variaveis preditoras para a ocorrencia de moluscos exoticos: nitrogenio total, salinidade, temperatura, cascalho e silte. As variaveis ambientais, juntamente com periodos de maior seca e caracteristicas naturais da regiao, (como a composicao mineral dos solos), favorecem a ocorrencia de moluscos exoticos em reservatorios do semiarido. EnglishWe assessed which environmental variables had the greatest influence on the occurrence of alien mollusks in reservoirs in the semi-arid region of Brazil during periods of drought. The study was conducted in the Argemiro de Figueiredo, Epitacio Pessoa, and Pocoes reservoirs in the Paraiba River watershed in northeastern Brazil during July and October/2015. Sampling was undertaken in three regions in each reservoir: 1) near the inflow from the principal tributary; 2) the mid-reservoir section; and, 3) near the dam. Three sampling sites were established in each reservoir region. The physical and chemical parameters of the reservoir waters in each site were measured and the granulometric compositions of their sediments determined. A total of 8635 benthic individuals were identified, of which 6569 were alien mollusks. Alien mollusks represented 90 % of all individuals collected from the benthic community in the Argemiro de Figueiredo reservoir, 63 % in Epitacio Pessoa, and 35 % in Pocoes. Melanoides tuberculata (6283 individuals) was the most abundant mollusk species, followed by Corbicula largillierti (286 individuals). Significant differences were observed in terms of the abundances of alien mollusks in the different reservoirs (p= 0.0001) and during the different sampling periods (p=0.0001), but not among the different sampling sites in each reservoir (p=0.937). In terms of environmental parameters, significant differences were observed in the different reservoirs (p=0.0001), but not in the different sampling sites in each (p=0.7428) or during the different samplings periods (p=0.346). The Best model (R2=0.61) selected five predictor variables for the occurrence of alien mollusks: total nitrogen, salinity, temperature, gravel, and silt. Environmental variables, together with periods of severe drought and the natural characteristics of the region (such as the mineral composition of the soils) favored the occurrence of alien mollusks in semi-arid reservoirs