In seawater, several trace metals with biological significance are highly complexed with organic matter. Marine cyanobacteria are an important phytoplanktonic group, with the ability to release trace metal-binding compounds to the seawater medium, which in turn modulates their bioavailability and influences their biogeochemical cycles. Such interactions may allow cyanobacteria to more easily access less available trace metals essential for their metabolic processes, or, conversely, keep the toxic forms of the trace metals from reaching intolerable levels. In this minireview, Cu and Fe interactions with cyanobacteria received special attention, although other trace metals (Co, Pb, Zn, and Cd) are also covered. Recent research has shed light on many aspects of trace metal-cyanobacteria ecology in seawater; nevertheless, the biochemical processes behind this dynamics and the structure of the vast majority of the metal binding compounds remain unclear.