Fe, Zn, Mn and N transfer between size classes in a coastal phytoplankton community: Trace metal and major nutrient recycling compared

Abstract

by D. A. Hutchins’ and K. W. BruIand2 ABSTRACT Experiments were performed to investigate transfer of 59Fe, 65Zn, 54Mn, and 15N from labeled cyanobacteria to the large ( > 8 pm or >5 km) phytoplankton size class from Monterey Bay, California. Transfer of metal isotope activity was measured from and into total (for all isotopes) and intracellular (59Fe only) pools. Results demonstrated rapid and efficient transfer of nitrogen to the large phytoplankton size class; intracellular 59Fe was transferred into the intracellular and total pools of the > 8 km phytoplankton size class 70% and 130% as efficiently as nitrogen, respectively. (jsZn and 54Mn were transferred between size classes 48% and 23% as efficiently as N. Extracellular 59Fe and 6sZn from the added cyanobacteria also appeared quickly in the large size fraction, although most of the Fe transfer appeared to be the result of surface adsorption rather than biological uptake. These data are discussed in relation to the biological recycling efficiencies of the four elements and the resulting implications for biogeochemical cycling of trace and major nutrient elements. 1. Introduction Biologically essential nutrient elements can become available to plankton commu- nities from either new or regenerated sources (Dugdale and Goering, 1967). Although exogenous inputs constrain the amount of export production from the ocean surface waters, regeneration and recycling support the bulk of primary productivity in most marine environments (Eppley and Peterson, 1979). Oceanogra- phers recognize that regeneration of major nutrient elements, particularly nitrogen, plays a crucial role in determining marine community structure and ecosystem dynamics. Recently, the concept of regenerated production has been extended to include recycling of biologically important trace metals. Hutchins et al. (1993) demonstrated that plankton communities from both coastal and open ocean areas are capable of regenerating and utilizing Fe incorporated into other living phytoplankton cells.