Enteromorpha flexuosa (Wulfen) J. Agardh (Chlorophyta : Ulvales): Evaluation as an indicator of heavy metal contamination in a tropical estuary

The use of bioindicators for contaminant monitoring is popular in all sectors of the environment but quite often bioindicators are utilised without rigorous evaluation of their viability as an indicator. We report field and laboratory investigations into the value of a commonly found macroalga, Enteromorpha flexuosa (Wulfen) J. Agardh (Chlorophyta: Ulvales) as an indicator of copper, zinc and lead contamination in a tropical estuary in Fiji. In the laboratory, metal content of E. flexuosa after 60 days of growth in seawater containing increasing concentrations of the metals showed almost perfect correlation with metal concentrations in water for all three metals, and concentration factors obtained were generally higher than values reported for other species of Enteromorpha. Performance in the field was evaluated by a one-year monitoring of metals in E. flexuosa, water and sediments from a contaminated estuary. Metal concentrations in water were always below detection limits and field concentration factors could not be determined but the concentration of lead in E. flexuosa showed a high correlation with the lead content of sediments. Lack of such correlation for copper and zinc in the field suggests that other environmental factors besides metal load in the physical environment could be controlling the bioaccumulation of these two metals. Whilst demonstrating E. flexuosa to be a viable bioindicator for lead, these results also highlight the need for proper assessment before an organism is considered for environmental monitoring.