INFLUENCE OF PHOSPHORUS STORAGE ON THE UPTAKE OF CADMIUM BY THE MARINE ALGA MACROCYSTIS-PYRIFERA

Seasonal changes in the concentrations of Cd and phosphate (P) in the macroalga Macrocystis pyrifera have been studied in Otago Harbour, a shallow marine embayment. Both components showed the same seasonal cycle, with concentration maxima during the austral winter (June-July) and summer periods (December-February) when growth of M. pyrifera was minimal. During these periods, cells contained significant quantities of electron-dense polyphosphate bodies (PPBs). Culture experiments showed that Cd uptake from seawater media was greatly enhanced when PPBs were induced to form. With 0.44 mumol Cd kg-1 in the medium, cultures forming PPBs contained 40-50 times as much Cd in excess of controls as those grown at the same Cd concentration in which PPBs were not formed. With 44 mumol kg-1 in the medium, PPB-forming cultures took up about twice as much Cd as those not forming PPBs. The incorporation of Cd into cellular PPBs may be an important mechanism for the uptake of this element even at natural Cd concentrations.