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.

Foraging dives of southern right whales (Eubalaena australis) in relation to larger zooplankton size prey availability in Golfo Nuevo, Península Valdés, Argentina

“…According to our data, DVM might explain the low density of E. lucens found in samples collected in previous studies in Golfo Nuevo 13 , 60 . It has been demonstrated that both juvenile and adult stages of E. lucens migrate extensively throughout the water column 82 and remained at or near the bottom during daylight hours and ascending toward the surface at night as shown for the Golfo San Jorge in Argentinean Patagonia 45 . Here, the highest abundance of E. lucens in older stages was found aggregated near the bottom.…”

“…This behavior involves a vertical migration to deeper waters before dawn and an upward migration at dusk towards the surface layer 41 , 42 . During DVM, zooplankton migrate to the surface to feed at night and then return to deeper depths to reduce predation risk from visual predators such as zooplanktivorous fish 43 – 45 . Studies have shown that larger zooplankton in advanced developmental stages, such as late juveniles and adults, tend to undergo DVM to greater depths compared to smaller individuals in earlier developmental stages 46 – 48 .…”

Size-related, seasonal and interdecadal changes in the diet of the Patagonian longfin squid Doryteuthis gahi in the South-western Atlantic

“…This coincides with the main depth range of Euphausia lucens (Gibbons et al ., 1991). Furthermore, D. gahi and Euphausiacea show the same diel vertical migration pattern (Nocera et al ., 2021). The SSC of D. gahi in 2020 fed on smaller amounts of Euphausiacea, due to lower abundances of Euphausiacea during winter (Sabatini & Colombo, 2001).…”

Spatial link between Adélie penguin foraging effort and krill swarm abundance and distribution

“…In terms of krill distribution, horizontal displacements over time are poorly understood. A key driver of horizontal advection is obviously oceanographic currents (Bestley et al, 2018;McBride et al, 2021;Nocera et al, 2021). However, krill can also swim at high speeds for extended periods of time against local currents (Krafft et al, 2015).…”