Trace Elements and Primary Production: Problems, Effects and Solutions

Abstract

The measurement of primary production in the ocean is basic to biological oceanographic processes. Factors which control primary production are varied, but include micronutrients (i.e., N and P) in sufficient supply, as well as many nanonutrients such as Cu, Mn and Zn. High levels of many of these trace constituents are toxic. Recent studies have shown that ambient concentrations of a number of nanonutrients in sea water are lower by an order of magnitude than previously believed. These findings present the potential for serious problems in terms of primary production measurements, since techniques used to measure production often employ various chemical reagents and sampling procedures that can contribute significantly to overall trace metal levels. We have been looking into various aspects of this problem, and will present our results concerning metal levels associated with accepted techniques used in primary production and many physiological studies that employ unialgal populations. We also present our results concerning the effects of Cu on primary production and total adenylate levels. Total adenylates have been used as a measure of the health of microbial populations using the concept of energy charge. Specifically, open-ocean phytoplankton were innoculated with Cu in the range of 0.012–5 µg Cu 1⁻¹. Estimates of primary production derived using metal-free collection and processing techniques as well as ATP, ADP, AMP and energy charge were determined. Copper additions as low as 0.25 pg 1⁻¹ (approximately 2 times ambient) reduced ¹⁴C uptake by 20%. Total adenylates were reduced 30% at a Cu concentration of 1 Pg 1⁻¹. However, the energy charge remained essentially unchanged over the range of Cu additions. The implications of these results are discussed.