Avoidance of hydrodynamically mixed environments by Mnemiopsis leidyi (Ctenophora: Lobata) in open-sea populations from Patagonia,Argentina

Biomass distributions of the ctenophore, Mnemiopsis leidyi, were collected during a week-long survey program in a tidal front along the Patagonian shelf in December 1989. Average ctenophore biomass concentrations varied significantly along a north–south gradient and in stratified compared to unstratified waters. The relative vertical distribution of M. leidyi biomass appeared to be constrained by surface levels of vertical shear. Vertical distributions of ctenophore biomass were highly variable at low levels of vertical shear (<4 s⁻¹) at the surface, but at higher levels of surface vertical shear ctenophores occurred deeper in the water column where shear levels were lower. These results indicate that physical conditions are important factors influencing the distribution of M. leidyi along the Patagonian shelf during summer months.