Cell size dependent toxicity thresholds of polycyclic aromatic hydrocarbons to natural and cultured phytoplankton populations

The toxicity of pyrene and phenanthrene to phytoplankton was studied by analyzing the effect on the growth, abundance and cell viability of cultured species and natural communities of the Atlantic Ocean and the Mediterranean Sea. A decrease in cell abundance, and growth rate was observed as concentration of PAHs increased, with catastrophic cell mortality induced at the highest PAH concentration tested. A strong positive linear relationship was observed between the LC50 (the PAH concentration at which cell population will decline by a half), and the species cell volume, for both phenanthrene and pyrene. Natural communities were however significantly more sensitive to PAHs than cultured phytoplankton, as indicated by the lower slope (e.g. 0.23 and 0.65, respectively, for pyrene) of the relationship LC50 vs. cell volume. The results highlight the importance of cell size in determining the phytoplankton sensitivity to PAHs identifying the communities from the oligotrophic ocean to be more vulnerable.This study was supported by a Spanish doctoral fellowship from the Conselleria d'Economía, Hisenda i Innovació del Govern de les Illes Balears, to P. Echeveste, and by the research projects “Thresholds of Environmental Sustainability (Thresholds)” 6th Framework Program, CE; and “RODA: Oceanic Eddies and Atmospheric deposition: Biological and Biogeochemical Effects in Superficial Waters of the East Atlantic” funded by the Spanish Ministry of Education and Science (CTM2004-06842-C03-02/MAR). We thank N. Berrojalbiz and S. del Vento for the contaminant solutions. We are grateful to the crew aboard the Garcia del Cid and Hesperides research vessels for their help during the cruises.Peer reviewe