Abstract
Organic chelators that are thought to be of recent biological origin control copper speciation in seawater. Previous studies have often resolved these copper binding ligands into two classes, class 1 ligands (conditional stability constants 10 12 –10 14 M −1 ) and class 2 ligands (conditional stability constants 10 9 –10 12 M −1 ). At present the sources and structures of these chelators are unknown. Previous work has shown that in response to copper toxicity, cultures of the marine cyanobacteria Synechococcus spp. produce a strong ligand, similar in binding strength to class 1 ligands. We extended this work by surveying a suite of copper‐stressed marine eucaryotic phytoplankton for the production of copper binding ligands. Most eucaryotic species we studied did not produce ligands with the binding strength of class 1 ligands, but many produced class 2 ligands. A marine dinoflagellate Amphidinium carterae was found to produce very strong ligands; however, the low abundance of dinoflagellates in the open ocean may mean that this source of class 1 ligands is more important in coastal waters. This survey shows that there are many biological sources of copper binding ligands, but that procaryotes such as cyanobacteria are more plausible sources of class 1 ligands in the open ocean than eucaryotes.