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 plank ton prey. Metal isotope activity incorporated into planktonic prey was added to bottles containing crustacean zooplankton grazers, and distr ibution of the added metals into dissolved, fecal pellet and grazer fr actions was monitored over time. At the end of a 9 to 10 h grazing per iod, concentrations of dissolved metal isotopes were approximately 3 t o 7 times higher in bottles with grazers than in control bottles witho ut grazers. An experiment in which flagellate grazers were fed Fe-labe led cyanobacteria suggested that protozoans may also remineralize trac e metals ingested with prey. Metal assimilation efficiencies from diat om and flagellate prey were determined in crustacean grazers; efficien cies generally decreased in the order Zn > Fe > Mn. These experiments indicate that biologically required trace metals behave much like majo r nutrients during grazing, and suggest that biologically mediated reg eneration and recycling could be an important part of the marine bioge ochemical cycles of Fe, Zn and Mn.