Vertical diel migration and feeding of Euphausia vallentini within southern Chilean fjords

E. vallentini is a circumpolar vertical migrator in the open ocean that enters the Chilean fjords through the sills to become the most common and abundant euphausiid. The diel migratory and feeding patterns of this species are studied in this distinct, enclosed and bathymetrically variable environment. The main goal was to determine the ability of E. vallentini to alter its vertical diel range in order to avoid shallow depths, or to maintain its depth migratory range and take advantage of benthic environment during daytime.Multiple opening closing nets sampled the water column in several basins along the Strait of Magellan. Fluorometrically determined stomach pigments along with on board experiments of evacuation rates allowed estimation of ingestion and consumption rates. Samples of stomach content were microscopically examined to compare day and night diet.E. vallentini migrated between the surface at night and 100-200 m in daytime. Surface night dwellers had higher chlorophyll stomach content than deep daytime dwellers. Diet composition changed from dinoflagellates and tintinnids at night, to a polychaeths-dominated diet in daytime. Stomach content, ingestion rates and consumption rates of phytoplankton were higher at night than in daytime, and accounted for an impact of 0.17% upon phytoplankton biomass.Changes of diet of E. vallentini imply unique adaptations to take advantage of both pelagic and demersal environments, which could explain its high abundance and high frequency of encounter within the southern Chilean fjords.