Inherent lack of CMFDA/FDA staining in certain algae and its implication for ballast water testing

Abstract

The approved method for testing the efficacy of ballast water management systems with respect to killing 10–50 μm organisms uses movements of the organisms or the vital stains CMFDA/FDA. The present study demonstrates that certain freshwater coccoid chlorophytes, known or suspected to contain a highly resistant cell wall component (algaenan), stain poorly with CMFDA/FDA, resulting in false negatives. The staining rates for the most dominant species were determined and were approx. 3–70 %. The use of Crystal Violet as an indicator for the presence of algaenan gave inconclusive results. The number of the 10–50 μm organisms in a small pond was found to be 10,183 organisms/mL (Lugol's fixed sample) vs. 2335 organisms/mL (CMFDA/FDA-stained sample). Using the staining rates obtained, it was estimated that the number of false negatives could make 40–50 %. The implications for biological performance evaluation of ballast water management systems are discussed.