Diurnal vertical migration of planktonic Ostracoda in IONESS system

The diurnal vertical migration of planktonic Ostracoda is studied based on the analysis of stratified samples of zooplanktons in the IONESS system. The whole taxa of planktonic Ostracoda migrates vertically and diurnally, its greatest abundance by day occurs at 200~300 m layer and decreases upward and at night occurs at 50~100 m layer but increases upward. Numerous species at the layers lower than the working layer ( 0~1 000 m) migrate upward at night to the layers shallower than 1 000 m. As a result, the total number of species in the working layer in creases sharply from 49 species by day to 78 species at night, with an increase amplitude of 60%. The number of species increases rather distinctly at various layers, firstly at the layer of 750~1 000 m with an amplitude of 150% and secondly at the layer of 50~100 m with an amplitude of 125%. Different planktonic Ostracoda takes different mode of diurnal vertical migration, agreat majority of species take the mode of upward migration at night, less number of species take insensitive mode and a fewer number of species take the mode of downward migration at night. The diurnal vertical migration of planktonic Ostracoda, which is distinct in this regard, is restricted in a certain water depth, demonstrating its features of stratified distribution. Ostracoda may be classified into four modes of distribution, namely, eurybathy distribution mode, upper layer distribution mode, mid-layer distribution mode and lower-layer distribution mode.