Assessing the toxic effects of dissolved copper on the Antarctic macroalga Desmarestia menziesii using chlorophyll fluorescence imaging in ecotoxicological tests

Abstract

Chlorophyll fluorescence was used to measure changes in the maximum fluorescence yield () and effective quantum yield (ΔF/) of Antarctic macroalgae in response to dissolved copper. Single-point measurements of ΔF/ of Desmarestia menziesii in concentration-response experiments were used to define the concentration where ΔF/ declined by 50% (EC50) after 6 h of exposure (3.9 mg L−1 ± 23% coefficient of variation (CV)). Fluorescence imaging experiments with the laminar algae Iridaea mawsonii and Himantothallus grandifolius neither showed any consistent pattern in spatial heterogeneity of fluorescence response, nor could EC50 values be obtained. However, imaging experiments on the terete D. menziesii resolved heterogeneity in fluorescence responses to dissolved copper with parameters declining more rapidly for thin thalli than thick thalli. While ΔF/ of thick thalli declined significantly after 7 days and provided an EC50 of 1.1 mg L−1 ± 29% CV, declining provide a lower and more precise nominal EC50 estimate after 7 days (0.061 mg L−1 ± 1% CV). These results demonstrate the importance of spatial heterogeneity in fluorescence of terete algae and suggest as a sensitive measure of toxic effects.