Estimating secondary production and egg production of Calanus spp. at the Polar front

The Barents Sea Polar Front is a biological hotspot, as the ice edge bloom happens in close
proximity to the front, while on the Atlantic side advection carries plankton towards the front.
It is of great interest to learn more about zooplankton secondary production in the region, as
this gives an indication of how much energy is available for higher trophic levels.

Secondary production and egg production of Calanus spp. was estimated across two transects
on the Atlantic side of the Barents Sea Polar Front during the spring bloom. The sampling
was done semi-automatic, with towed instrument packages recording amongst other
zooplankton biovolume with the LOPC, fluorescence and temperature. This in turn was used
to compute growth rates using a semi-empirical formula, which were applied to the observed
biomass of zooplankton. In addition, biovolume spectrum was constructed to further
understand the state and size structure of the zooplankton community.

At different stations female Calanus spp. were collected to measure egg production rate, which in combination
with abundance counts from the LOPC gave estimates of Calanus egg production across the
transects. Secondary production in the upper 50 meters of the water column was estimated to
be on average 5 and 6 mg carbon m-3 day-1 across the first and second transect, respectively.

Contribution of egg production to total secondary production was highest on the second
transect, but the method could be prone to overestimation of egg production. The biovolume
spectra indicated productive zooplankton communities typical for a spring bloom scenario.
This study demonstrates the strengths of using semi-automatic sampling to discover spatial
patterns in zooplankton secondary production