GRAZER-MEDIATED REGENERATION AND ASSIMILATION OF FE, ZN AND MN FROM PLANKTONIC PREY

Experiments were performed to investigate grazer remineralization and assimilation of Fe, Zn and Mn from autotrophic and heterotrophic plankton prey. Metal isotope activity incorporated into planktonic prey was added to bottles containing crustacean zooplankton grazers, and distribution of the added metals into dissolved, fecal pellet and grazer fractions was monitored over time. At the end of a 9 to 10 h grazing period, concentrations of dissolved metal isotopes were approximately 3 to 7 times higher in bottles with grazers than in control bottles without grazers. An experiment in which flagellate grazers were fed Fe-labeled cyanobacteria suggested that protozoans may also remineralize trace metals ingested with prey. Metal assimilation efficiencies from diatom and flagellate prey were determined in crustacean grazers; efficiencies generally decreased in the order Zn > Fe > Mn. These experiments indicate that biologically required trace metals behave much like major nutrients during grazing, and suggest that biologically mediated regeneration and recycling could be an important part of the marine biogeochemical cycles of Fe, Zn and Mn.