Searching for Algaecide or Algaestatic Effects of Several Plant Extracts on Phytoplankton: Preliminary Results

Aims: Evaluate the in vitro effects of essential oils and water extracts of Laurus nobilis, Rosmarinus officinalis, Mentha suaveolens and Fraxinus angustifolia on the growth of Anabaena cylindrica and Chlorella vulgaris.

Study Design: Experimental research.

Place and Duration of Study: The cyanobacterium Anabaena cylindrica and the green alga Chlorella vulgaris were used as test strains to evaluate the effects of plant extracts on algal growth. All experiments were undertaken in the Agricultural School of Bragança - Polytechnic Institute, from September 2010 to July 2011.

Methodology: Essential oils were obtained by means of hydrodistillation of the plants. The oils and the water that remained, after the hydrodistillation, were further used for the growth screening of Anabaena cylindrica and Chlorella vulgaris under axenic cultures. Both types of extracts were tested at different concentrations. The essential oil effects were evaluated by disc diffusion method and water extracts effects were evaluated in batch cultures.

Results: Essential oils had an algaecide effect in all tested concentrations (1:1; 1:3; 1:4 and 1:10) for both algal strains. Contrarily, none of the water extracts evidenced a complete algaecide effect. Nevertheless, promising results were obtained with rosemary water extract since the highest concentrations (1:4) had an algaestatic effect on C. vulgaris. Conversely, the observed effects on A. cylindrica varied from cellular density decrease to an algaestatic effect. Therefore, the tested algal strains presented distinct responses to both extract types and concentrations.

Conclusions: Comparing the different extracts’ activity, it can be concluded that essential oils mostly influenced algal growth.