Toxicity of commercial cypermethrin on the growth of three marine microalgal species, Skeletonema costatum (Bacillariophyceae), Scrippsiella trochoidea (Dinophyceae) and Chattonella marina (Raphidophyceae) was separately investigated by 96 h and 24 d growth tests. The growth was stimulated at low concentrations and inhibited under high concentrations; however, overcompensation was observed at the late period of exposure under high concentrations in 24 d growth tests. The highest stimulation rates were obtained at concentration of 5 microg/L. The 24 h SC10 values were 0.91, 4.17 and 20.4 microg/L for S. costatum, S. trochoidea and C. marina, respectively. The 96 h IC50 values were 75.3, 227 and 114 microg/L for the three species, respectively. Results suggest that cypermethrin level used for sea lice controlling exert a stimulative effect on phytoplankton growth, and might result in the succession of phytoplankton community structure due to different sensitivity of species.
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