We present an overview of the oceanic chemistries of the bioactive trace metals, Mn, Fe, Co, Ni, Cu, and Zn; we combine field data with results from laboratory phytoplankton culture-trace metal studies and speculate on the potential influences of these trace metals on oceanic plankton production and species composition. Most field studies have focused on the effects of single metals. However, we propose that synergistic and antagonistic interactions between multiple trace metals could be very important in the oceans. Trace metal antagonisms that may prove particularly important are those between Cu and the potential biolimiting metals Fe, Mn, and Zn. These antagonistic interactions could have the greatest influence on biological productivity in areas of the open ocean isolated from terrestrial inputs, such as the remote high nutrient regions of the Pacific and Antarctic Oceans. The emerging picture of trace metal-biota interactions in these oceanic areas is one in which biology strongly influences distribution and chemical speciation of all these bioactive trace metals. It also seems likely that many of these bioactive trace metals and their speciation may influence levels of primary productivity, species composition, and trophic structure. Future investigations should give more complete consideration to the interactive effects of biologically important trace metals.Biological processes can strongly influence the oceanic chemistries of trace metals, and, in turn, trace metals can influence plankton production and community structure. These interactive influences are particularly important for six metals of the first transition series which are required by phytoplankton for various metabolic functions: Mn, Fe, Co, Ni, Cu, and Zn. A deficiency of these "bioactive" trace metals may limit oceanic plankton production (Brand et al. 198 3), and an excess of certain of these same metals may inhibit plankton growth (Brand et al. 1986; Sunda 1988 Sunda -1989.Our knowledge of the oceanic concentrations, distributions, and cycles of trace metals has advanced significantly (see Bruland 1983; Whitfield and Turner 1987). We now know the bioactive trace metals exist at nanomolar (1 Om9 M) to picomolar ( lo-l2 M) concentrations in oceanic waters. In addition, marine chemists have recently advanced their ability to characterize the chemical speciation of these bioactive trace metals in the sea; that is, we can now determine their free ion concentrations and the extent to which certain trace metals interact with organic and inorganic ligands naturally present in oceanic surface waters. Results from laboratory studies on the relationship between dissolved trace metal concentrations and phytoplankton growth have emphasized the importance of the chemical speciation of trace metals in the external milieu of these organisms (Huntsman and Sunda 1980; Morel and MorelLaurens 1983; Sunda 1988 Sunda -1989.As a result of these advances, we now realize that the concentrations of the bioactive metals are much lower and that chemical...
