Elemental composition of mantle tissue granules in Hyridella depressa (Unionida) from the Hawkesbury-Nepean River system, Australia:: inferences from catchment chemistry

The Australian freshwater mussel Hyridella depressa sequesters elements in calcium phosphate (CaP) granules that form extensive aggregations in its tissues. Elements contained in these granules were determined by X-ray microanalysis of river and lake mussels from the Hawkesbury-Nepean River system, New South Wales. Granules in freeze-substituted mantle tissue were analysed to determine the variation in element profiles in granules among mussels and among sites. For the common elements Ca, P, Fe, Mg and Mn, granule composition reflected catchment lithology and site trophic status and indicated exogenous input. These were most important for differentiation among lake sites and also indicated differences between lake and river mussels. Site differences seen with some common elements in granules from lake mussels correlated with differences in water chemistry. Trace elements, particularly Al, Cu, Zn and Pb, were also important in lake and river site differentiation. The granules play a major role in element dynamics in freshwater mussel tissues and provide a focal structure for direct analysis of element accumulation by these bivalves. The results indicate that characterization of element content of granules in mussel populations would provide valuable insights into animal-element interactions in freshwater systems for ecological and ecotoxicological investigations.