5-MHz acoustic-backscatter measurements of Cochlodinium polykrikoides blooms in Korean coastal waters

Abstract

The toxic, chain-forming dinoflagellate Cochlodinium polykrikoides blooms annually in the coastal waters of Korea and has a serious impact on coastal fisheries and the surrounding ecosystem. Measurements of the acoustic volume-backscattering strength of C. polykrikoides blooms were made using 5 MHz signals at sites located off the coast of Geumo Island, Korea. An optical microscopic method was used to estimate the abundance of phytoplankton in coastal areas from water samples collected simultaneously with the acoustic measurements. Background scattering strengths at sites where there were no blooms were less than -42 dB re 1 m-1. In contrast, backscattering strengths measured in bloom areas increased rapidly, showing a high correlation with dinoflagellate concentrations. The measured volume-backscattering strengths were compared with those predicted from a fluid-sphere scattering model; the results implied that the chain-forming cells should be viewed as a single sphere with an equivalent radius. The results suggest that it may be possible to apply an acoustic technique to the real-time detection of harmful algal blooms. © 2010 International Council for the Exploration of the Sea.