Toxicity of copper, nickel and zinc to Synechococcus populations from the Strait of Gibraltar

During an Oceanographic Cruise in September 2008, picophytoplankton samples from two sites of the Strait of Gibraltar (one from the Atlantic (35°57′16″N, 5°49′41″W) and the other from the Mediterranean (36°00′48″N, 5°15′04″W)), were exposed to 72 h toxicity tests with copper, nickel and zinc. Collected samples were analysed by flow cytometry (conferring information of size, chlorophyll a and pigments), distinguishing a group that matches with Synechococcus population of oceanic waters with a high phycoerythrin signal, in all surface and deep chlorophyll maximum samples (DCM).Results data, for all metals studied, showed differences in either growth or signals corresponding to chlorophyll a content, phycobilins and cellular volume, between samples from the Atlantic and Mediterranean, while no significant differences were observed between populations from surface and deep chlorophyll maximum samples. Copper was the most toxic metal, of the three studied, with EC50 growth rate inhibition values of 4 μg L−1 for the surface Atlantic water samples, and up to 15 μg L−1 for those from the DCM Mediterranean water samples. For the other two metals studied less than 50% growth rate inhibition was found, in all cases, for concentrations studied up to 700 μg L−1. All three metals shared an increase of size when exposed to metal concentrations, even in cases where growth rate inhibitions were less than 20% (Zn); on the other hand, in the case of chlorophyll a and phycoerythrin signals there seemed to be a decrease with increase of metal concentration.

Research Highlights
► Toxic effects of Cu, Ni and Zn on natural picoplankton populations.
► Different toxic effects of these belonging to different sampling locations.
► Population growth inhibition, cell size, and pigments as toxicity endpoints.
► Cu as the most toxic of these three metals studied.