Size and stage specific patterns in Salpa thompsoni vertical migration.

Vertical distribution and size-dependent migrations of the pelagic tunicate Salpa thompsoni were studied during late summer to early autumn (26th February – 15th March 2018) at contrasting hydrological stations over the Kerguelen Plateau (Southern Indian Ocean). Vertical migrators, such as S. thompsoni , have potentially significant impacts on the biological pump because of their large swarms, high grazing/fecal pellet production rates and extensive vertical migrations. S. thompsoni were undergoing diel vertical migration from a daytime weighted mean depth of ~450 m to a nighttime weighted mean depth of ~100 m. Smaller blastozooids and oozoids were the strongest vertical migrators, while their larger counterparts did not show a consistent diel cycle in their vertical distribution. Strong vertical migrations of the smallest blastozooids and oozoids imply high predation pressure on these groups. This knowledge has implications in modelling salp contributions to the vertical passive and active carbon fluxes. • This is the first study of size-dependent vertical migration of Salpa thompsoni. • Salpa thompsoni were undergoing diel vertical migration between 450 and 100 m. • Smaller individuals were the strongest migrators implying higher predation pressure. • There was no consistent cycle in vertical distribution for large individuals. • Understanding migration patterns has implications in carbon flux modelling. [ABSTRACT FROM AUTHOR]