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.