Expansão populacional de Corbicula fluminea (Müller,1774) no médio Rio Teles Pires (Mato Grosso, Brasil) : a influência de características do sedimento

Abstract

Corbicula fluminea is an exotic species of bivalve mollusk native to the Asian continent. This species has high fertility, incubate their larvae and is considered a successful invader in the Americas and Europe. The aim was to evaluate the establish, structure and development of the population of Corbicula fluminea in the Teles Pires river in the state of Mato Grosso, Brazil. Three hypotheses were tested: 1 - The density and the area occupied by C. fluminea increased from 2006 to 2012; 2 - The shell length of C. fluminea increased from 2006 to 2012 and 3 - The grain size and organic matter content determine the distribution and density of C. fluminea in the Teles Pires river. We sampled 10 pre-selected sites in the region of the middle Teles Pires river, comprising three regions 1, 2 and 3. The sampling effort was standardized by the number of dradges, distance and mesh of the sieve, obtaining a longitudinal profile, upstream-downstream. The length (Lt, mm) and weight were measured. From the biometric variables was calculated the condition factor. The biometric relations were observed across regressions, analysis of variance and principal component analysis. The sediment was characterized from particle size analysis and organic matter content. We measured the depth and transparency at collection sites and the physical-chemical composition BOD (mg / L), nitrite (mg / L), nitrate (mg / L), total phosphorus (mg / L), solid ( mg / L) and calcium (mg / l)) for each region. The average density of C. fluminea in 2006 was 6.36 and increased to 26.42 ind/m2 ind/m2 in 2012. The highest density was found at beach 8 and smaller in the beaches 7 and 10. The mode of the distribution by length increased from 20.00 in 2006 to 30.00 mm in 2012 mm. The average length (± standard deviation) increased from 18.61 ± 7.02 mm to 26.07 mm ± 4.63 in the same period. The condition factor was higher in the third and there were significant differences between the beaches (p = 0.01). There was predominance of clay in eight of the ten beaches, with an average of 70.96%, and the sediment was characterized as inorganic. The density varied significantly when analyzed in relation to grain size, demonstrating a positive relationship with the intermediate particles and negative with clay. In 2006 C. fluminea was first collected from Teles Pires river. From 2006 to 2012 recorded the species dispersion and occupation of new environments was registered, with high density in the interval between collections. C. fluminea is an exotic species in the region and one of the most common invasive freshwater ecosystems worldwide. Variation in the size of the shell may be associated with differences in abiotic and biotic factors. The differences in particle size show that the middle rio Teles Pires has distinct, alternating locations with local rock formations with sand accumulation. From 2006 to 2012, a change in the granulometric composition of the sediment can be observed. The positive relationship of the density of C. fluminea with fine sand may indicate that this condition can be considered preferred for this species. The organic matter content shows no relationship with clam density and thus not a determining factor for its distribution. The region 2 comprising beaches 5, 6, 7 and 8, provides best conditions for the establishment, where larger phosphate levels occur. As population growth is similar the estimated exponential growth can indicate the absence of limiting factors to their establishment and development. For an exotic species and invasive this ensures sufficient means to dominate the colonized environment.