Picture: Iceberg in the Arctic. Credit: Jean-Christophe André.

One of the main factors influencing the zooplankton community at high latitudes is strong seasonality. At 80–82°N, the period of a polar night without sunlight lasts for up to 4 months, although marine organisms may experience darkness for a longer time depending on sea ice and snow cover. The strong seasonality in algal blooms results in a short and pulsed appearance of the large, predominately herbivorous zooplankton in surface waters during the spring.

However, the annual timing of the zooplankton ascent from their winter sleep at depth differs from year to year and among regions. The question is whether changes in the timing of algal blooms due to climate change are leading to a mismatch for seasonal zooplankton ascent and reproduction.

This study looks at 6 months of under-ice zooplankton observations from the N-ICE2015 expedition from January to June 2015 in the Eurasian sector of the Arctic Ocean north of Svalbard.

Algal food availability, which was closely linked to seasonality, explained the community changes seen in surface waters in May and June due to the seasonal ascent followed by feeding of zooplankton.

Seasonal changes from winter to spring mostly involved an increase in the herbivorous C. finmarchicus in the upper 200 m of the water column coinciding with the peak of the phytoplankton bloom in late May.

The Yermak Plateau and adjacent Nansen Basin were characterised by oceanic North Atlantic and Arctic species, many of which are deep water specialists. Despite the late onset of the spring bloom due to consolidated sea ice, both North Atlantic and Arctic species successfully reproduced in the study area.

Future prospects of less sea ice and earlier onset of the algal bloom will likely be positive for both Arctic and boreal zooplankton in this region. The deeper zooplankton fauna, below 200m depth, is expected to persist into the future with little change in communities.

  • Paper: Hop H, Wold A, Meyer A, Bailey A, Hatlebakk M, Kwasniewski S, Leopold P, Kuklinski P and S reide JE (2021) Winter-Spring Development of the Zooplankton Community Below Sea Ice in the Arctic Ocean. Front. Mar. Sci. 8:609480. doi: 10.3389/fmars.2021.609480