ADCP observations of Diel Vertical Migration of Biological Layers in Gulf of Gdansk.

The study of Diel Vertical Migration (DVM) of biological organisms is important for a better understanding of different aspects of Baltic Sea ecosystem function, including the behavior of biological organisms as well as the marine carbon budget, which could be under DVM impact. Ecosystem of the semi enclosed Baltic Sea is especially sensitive to human impact. Its monitoring is important and requires rapid, relatively effortless and non-invasive techniques. Hydroacoustic methods meet these requirements. The main objectives of our research was, basing on hydroacoustic technique, to determine the DVM velocities of Baltic biological organisms and understand the impact of environmental factors (salinity, temperature) on the magnitude of the Diel Vertical Migration. The ADCP data (volume backscattering strength and the DVM velocities), collected near Hel Peninsula from April 05 2014 to April 06 2014, were used in the analysis. The ADCP, working at the frequency 300 kHz, was placed on the seabed. Three methods differing in used measurement data, were applied to determine the DVM velocities. The distinction between the results obtained using different methods was discussed.