The effects of oil spill chemicals on CO2 assimilation by the fruticose lichen Cladina mitis

Abstract

The effects of three oil spill dispersants (Corexit 9600, 9550 and 7664) on carbon fixation by the fruticose lichen Cladina mitis were examined in order to provide insights into the potential risks associated with dispersant use in and around freshwater systems. Cladina is a common plant of northern freshwater shoreline communities. Treatments with the undiluted dispersants inhibited rates of carbon fixation by 60% to 80% and bleached portions of the thalli when applied at doses less than 10 mg g⁻¹ dry weight (approximately 2·5 mg cm⁻² on an aerial basis). Since the recommended field application rates for the dispersants range from 0·2 to 3 mg cm⁻², there is a distinct possibility that misapplication (direct spraying) may be detrimental to populations of Cladina. However, the inhibitory effects were not lethal in all cases and partial recovery of the lichens was noted within 3 weeks after treatment. The potential impact of dispersant use in freshwater systems on the shoreline plant communities is discussed in the light of our findings.