Seasonal and day–night changes in the vertical distribution of Gnathophausia longispina and G. elegans (Peracarida, Lophogastrida) in the East China Sea

Abstract

Abstract Seasonal and day–night changes in the vertical distribution and habitat of mesopelagic crustaceans, Gnathophausia longispina and G. elegans were investigated in the East China Sea during four oceanographic cruises carried out between May 2012 and January 2013. The abundance of G. elegans was approximately one-tenth that of G. longispina, although both species appeared throughout the year. The main distribution range of G. longispina was 100–600 m, and G. elegans was 600–700 m. Only G. longispina showed ontogenetic differences in diel vertical migration (ODVM); most individuals inhabited depths of 500–600 m during the day and 100–400 m at night when younger individuals inhabited shallower layers than mature individuals. Overall, both species showed a small overlap in their vertical distribution at around 600-m depth. Vertical segregation of habitat could have facilitated the sympatric biogeographic distribution of these two congeneric species around the West/Central Pacific Ocean.