Fuel toxicity on Isochrysis galbana and a coastal phytoplankton assemblage: growth rate vs. variable fluorescence

Laboratory cultures of the flagellate Isochrysis galbana and a coastal phytoplankton assemblage were used to assess the feasibility of variable fluorescence (F(v)), measured by means of fast repetition rate fluorometry, as endpoint to monitor the effect of fuel on microalgae as compared to phytoplankton growth rate. Parallel changes in cell size of I. galbana and taxonomic composition of the natural assemblage were recorded. The results presented in this investigation indicate that F(v) is a suitable endpoint to this aim, due to the ease and rapidity of the measurement, ecological relevance and sensitivity. The derived effective concentrations provided toxicity thresholds similar to, or even lower than concentrations derived from embryo-larval bioassays with marine organisms. The lowest calculated EC(10) corresponded to that of the natural assemblage, 2.5 microg eq chrysene L(-1), concentration easily exceeded in high maritime traffic areas subjected to frequent spillages.