The Southern Polar Front as a key to mesoplankton migratory behavior

Andrey Vedenin,Alexander Vereshchaka,Eteri Musaeva,Dmitry Kulagin

doi:10.1038/s41598-020-70720-9

Andrey Vedenin, Alexander Vereshchaka + Show 2 more

Open Access

https://doi.org/10.1038/s41598-020-70720-9

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Abstract

Diel and seasonal vertical migrations of zooplankton represent a widespread phenomenon occurring in marine and freshwater environments. Diel migrations are panoceanic, while seasonal migrations usually occur in temperate and polar areas. This paper describes differences in the diel and seasonal vertical migrations in the Drake Passage north and south of the Polar Front (PF). We analyzed material of 85 stations collected in spring of 2008 and 2010 (October–November) and in summer of 2010 and 2011 (January) within the 0–300 m depth range during various time of a day. At each station we sampled the upper mixed (UL), the middle (ML), and the deeper layers (DL) bounded by hydrological gradients. Diel migrations were significantly different south and north of the PF in terms of total abundance, biomass, diversity and individual taxa density. In both seasons, mesoplankton dielly migrated between the ML/DL and the UL north of the PF and between layers below 300 m and the DL and ML south of the PF. Deeper range of diel migrations south of the PF was coupled with a general mesoplankton descent in summer period compared to spring. Conversely, north of the PF, mesoplankton ascended to upper layers in summer, which was mirrored in lesser depths of diel migrations. The differences in the plankton distribution on both sides of the PF are likely associated with variations of vertical distribution of phytoplankton. Some abundant taxa such as Aetideus sp. and Oithona plumifera showed both common (nighttime ascend) and inverted (nighttime descend) vertical migrations depending on season and position related to the PF.

Highlights

Diel and seasonal vertical migrations of zooplankton represent a widespread phenomenon occurring in marine and freshwater environments
Trends were similar in the ML on the both sides of the Polar Front (PF) and opposite in the deeper layers (DL) north and south of the PF
Both abundance and biomass increased around midnight in the DL south of the PF and decreased north of the PF (Fig. 2)

Summary

Introduction

Diel and seasonal vertical migrations of zooplankton represent a widespread phenomenon occurring in marine and freshwater environments. Seasonal migrations of zooplankton to the surface waters for feeding and reproduction take place in temperate and polar areas, and are usually driven by phytoplankton bloom[16]. In the Southern Ocean, phytoplankton spring and summer blooms occur in a rather thin upper mixed water layer < 100 m17, which results in an extensive ascent of the zooplankton to the upper waters with maximum densities in the upper 50 m16. Both diel and seasonal migrations are greatly influenced by environmental factors including local hydrological conditions. Zones between the fronts represent biogeographic areas of the Southern Ocean, the PF marks one of the boundaries between the subantarctic and antarctic plankton a ssemblages[20,21,22]

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