Zooplankton and fishes found below a depth of 200 m may perform a vertical migration to the surface waters. The migration patterns (from 400 m to the surface) of four groups of organisms were studied in the deep (1500 m) eastern Mediterranean (Cretan Sea) for 2.5 years. The lunar cycle, daylight duration, cloudiness and presence of predators and prey explain their migration variability. This phenomenon is important as it constitutes an active transport of organic matter over large distances.