Abstract
The provision of sediment in rivers, due to erosion processes that occur in the environment, consists of a major source of pollution and alteration of the physicochemical conditions of water resources. In addition, the increase in water turbidity may cause siltation, dramatically impacting aquatic communities. Specifically considering the bivalve Corbicula fluminea (Müller, 1774), the aim of this study was to analyse the effect of exposure to different turbidity conditions of sediments, as a risk factor for the animals. For this purpose, a docking device was designed to ensure water circulation in a closed system and to maintain the desired levels of turbidity. Although C. fluminea can generally tolerate environmental changes in aquatic systems, an intolerance to high turbidity levels was experimentally observed, expressed by the mortality rate of the animals when exposed to conditions above 150 nephelometric turbidity units (NTU). This value was similar to the one recorded at study sites in the rivers Pardo (Serrana-SP-Brazil) and Mogi Guaçu (Porto Ferreira-SP-Brazil) during the rainy season. Using a logistic regression model, the experimental results were analysed and the observed mortality rates indicate that the exposure of the animals to turbidity levels above 150 nephelometric turbidity units (NTU), for periods longer than 120 hours, may be considered a probable cause of mortality for the species.
Highlights
Corbicula fluminea (Müller, 1774) (Bivalvia: Corbiculidae) is an exotic species which was introduced in South America in 1970 (Ituarte, 1981), probably by means of ballast water from ships entering the Rio da Prata estuary (Mansur et al, 2004)
This study found data to support the idea that an increase in turbidity levels can be linked to higher mortality rates for the C. fluminea species
This helps to explain a seasonal decline in the population, especially during the period of intense hydro-meteorological events (November-January), due to the fact that both the studied watersheds have a high potential erosion risk
Summary
Corbicula fluminea (Müller, 1774) (Bivalvia: Corbiculidae) is an exotic species which was introduced in South America in 1970 (Ituarte, 1981), probably by means of ballast water from ships entering the Rio da Prata estuary (Mansur et al, 2004). This species has been the subject of a great deal of research due to its capacity to spread over large areas and become an important competitor with native species of freshwater bivalves, potentially causing. Freshwater bivalves generally live buried in muddy or sandy riverbeds, at depths which vary according to the size of the specimens. C. fluminea does not show any preference for a particular sediment texture (Belanger et al, 1985), substrate, or vegetation cover, showing a high level of resistance to changes in physical-chemical parameters of water temperature and salinity (Kat, 1982)
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