Krill diel vertical migration in Southern Patagonia

Abstract

Diel vertical migration (DVM) of krill was studied throughout 36 h at a fixed station (46.05°S, 66.19°W; 98-m depth) located in the center of the San Jorge Gulf, Southern Patagonia area, during February 2014. Using an echosounder system, combined with an autonomous Video Plankton Recorder (Auto-VPR) and Jacknet samplings, we describe the migration pattern, the associated biomass and the macrozooplankton species involved. The net sampling and the Auto-VPR images allowed us to identify the krill species detected in the echosounder signals, which corresponded to Euphausia lucens, Euphausia vallentini and Nematoscelis megalops. The krill community followed a "normal pattern"of DVM, ascending at dusk (∼18:30 h) and descending at dawn (∼06:30 h), forming a dense layer near the bottom during the day. Krill vertical migration speed was estimated from the echogram data at ∼ 1 cm s-1 (1 body length per s for 1-cm-long animal), and the integrated mean biomass was 57.8 g m-2. This study provides a description of temporal and spatial patterns of krill vertical distribution, which should be taken into account when studying the complexity of the SJG ecosystem dynamics and carbon flux.