Application of Acoustic Doppler Current Profiler (ADCP) to Observe Diel Vertical Migration of Zooplankton

Study of zooplankton behavior was observed because of their importance as a source energy for small fish and other organisms in the food chain. The aim of this study was to investigate diel vertical migration (DVM) of zooplankton using high frequency acoustic scattering techniques from an acoustic Doppler current profiler (ADCP) instrument. The DVM was observed by utilizing mean volume backscattering strength (MVBS) from the recorded ADCP's echo intensities. MVBS data were obtained using a bottom-moored, upward looking 750 kHz ADCP at 15 m depth in Lembeh Strait, North Sulawesi, Indonesia. In this work, we simultaneously presented ADCP quantifications, zooplankton net samples, and oceanographic data (tidal and water current). The movement of zooplankton was shallower during the night and deeper during the day with changes of MVBS and ranged between -65 and -80 dB. From laboratory analysis, it was found that crustacean had the highest abundance and biomass, dominated at different time during the observation. However, further research should be performed with specific species using measured sound speed and density of zooplankton and laboratory analysis for grazing angle measurement should be conducted in order to improve accurate results of specific zooplankton.