Copper complexing properties of exudates and metabolites of macroalgae from the Aegean Sea

Macroalgae are a significant source of extracellular organic material in the coastal areas of the Mediterranean, including organic ligands which serve as modulators of metal complexing capacity. This paper examines the release of copper-complexing ligands by 24 macroalgal species, including chlorophyta, rhodophyta, ochrophyta as well as Posidonia oceanica, common throughout the Mediterranean. Metabolites isolated from the algae Dictyota dichotoma and Pterocladiella capillacea were examined for the first time regarding their Cu-complexing properties. The concentration of ligands (LT) and the copper-binding strength (log Kapp) of exudates and metabolites were determined by electrochemical methods.All algal species released ligands giving LT concentrations ranging from 109 to 744 nM in unfiltered samples. An increase in the concentration of ligands up to 15 times in comparison to the blank was observed after 48 h of culturing macroalgae in artificial seawater. The binding strength (log Kapp) varied among species from 7.0 to 8.6, except for the metabolites for which it was lower (log Kapp = 6). Most of the ligands released were in the dissolved phase, with the contribution of particulate and/or colloidal organic matter (up to 46% of total ligands) appearing to be important only in specific macroalgal species.

► Cu complexing properties of exudates and metabolites from macroalgae were examined.
► Cu ligands released from all algal species range from 109 to 744 nM.
► Most of the ligands released were in the dissolved phase.
► Specific electrochemical methods provide information of the type of organic matter.
► Isolated polysaccharides, fucoidans and alginates, provide Cu complexing sites.