Contrasting diel vertical migration patterns in Salpa fusiformis populations

Vertically stratified zooplankton sampling at three locations in the Catalan Sea demonstrated that the coexistence of two diel vertical migration patterns in Salpa fusiformis populations. Salps migrated to the surface during the day (reverse migration) at one station while they swam to surface layers at night (nocturnal migration) at the other two stations. While nocturnal migration was significant at the deepest station, reverse and nocturnal migrations at shallow stations were weak. Our data support the idea of reproductive, surface aggregation in this species, with a possibility that the larger individuals hit the bottom at the shallower stations, resulting in an apparently random migration pattern.