Metal concentrations in crayfish tissues in relation to lake pH and metal concentrations in water and sediments

Abstract

Cambarus bartoni from two acid lakes, Cambarus robustus from one acid lake, and Orconectes virilis from one acid and two circumneutral lakes were analyzed for the following concentrations: Mn, Fe, Al, Zn, Cu, and Cd in gill; Mn, Fe, Al, Zn, and Cu in muscle; and Mn, Al, Fe, Zn, Cu, Ca, Mg, Ba, and S in carapace tissue. Analysis of covariance and canonical variates analysis were used to illustrate differences in the six crayfish populations, based on the elemental content of the three tissues. Gill Cd was significantly greater in all four crayfish populations from the acid lakes, as compared to crayfish from circumneutral lakes. Subsequent canonical variates analysis separated crayfish from acid lakes from those sampled from two circumneutral lakes, based on gill Cd concentrations and to a lesser extent on gill Mn concentrations. Carapace elemental composition was also significantly different among the six crayfish populations, with the canonical variates analysis separating crayfish of acid-lake origin from those captured in circumneutral lakes, based on differences in Mg and Mn content of the carapace; carapaces of crayfish from acid lakes had more Mn and less Mg relative to crayfish carapaces from circumneutral lakes. The elemental composition of crayfish muscle was the least variable and the least indicative of differences in elemental content among the six populations. Conditions of low pH may be preventing the normal mineralization of crayfish carapaces, as evidenced by crayfish from acid lakes having carapaces with lower Mg concentrations relative to crayfish from circumneutral lakes. More importantly, however, increases in gill Cd in crayfish from low-pH lakes appear to be a pH-related effect rather than being attributable to differences in Cd accumulation among species or to abiotic factors such as concentrations of Cd in the sediments, dissolved organic carbon, or water-borne Ca concentrations. As crayfish are an important food resource for many fish and semiaquatic animals, they could be a key vector in the trophic transfer of Cd from the aquatic to the terrestrial environment.