Environmental effects on zooplankton abundance on a sub-Arctic shelf off northern Norway

Abstract

We studied the abundance of common zooplankton on 8 dates and at 5 locations on the shelf off the Lofoten Islands, northern Norway, between September 2013 and August 2014. We tested for relationships between environmental variability and abundances. We found that, of 17 zooplankton taxa or groups for which we recorded abundances, 4 omnivorous or carnivorous groups persistently differed in abundance between stations. This difference probably reflected relatively deep centres of distribution in the water column, and abundances of these species were positively associated with bottom depth. In 10 taxa or groups, abundance correlated with sampling date or temperature, salinity, or fluorescence, but generally not with bottom depth. Most of these taxa were consumers on low trophic levels, with a vertical distribution often associated with near-surface waters. In the remaining taxa or groups, no association between abundance and the environment or with time of sampling was established. Our results suggest that on-shelf abundances of zooplankton with intermediate-to-deep vertical distribution patterns are mainly limited by bathymetry, while abundance variations in zooplankton with a predominately near-surface distribution are driven by intra-annual environmental variability.

Seasonal dynamics of mesozooplankton biomass over a sub‐Arctic continental shelf

“…While the abundance and the seasonal pattern of the numerically dominant holoplankton taxa and cod larvae was similar in 1949/1950 and 2013/2014 (Eiane et al, 2018;Wiborg, 1954), meroplankton has become a more abundant component of the zooplankton community (Silberberger et al, 2016). In 2013/2014, the annual average contribution of meroplankton to the mesozooplankton abundance was approximately 20% closer to the coast and around 5% over the central shelf (Eiane et al, 2018;Silberberger et al, 2016). Accordingly, a more important ecologic function of meroplankton in the Lofoten-Vesterålen region can be assumed.…”

“…It is an important fish spawning ground and larval drift area where first feeding fish larvae need to encounter suitable prey. The area is north of the Arctic Circle and is subject to strong seasonality in day length, temperature, and primary production (Eiane et al, 2018). Two major northward flowing currents, the Norwegian Atlantic Current (NAC) and the Norwegian Coastal Current (NCC), together with strong tidal forces, shape the hydrography of the region, causing an overall northward transport with retention of planktonic organisms over the shelf (Espinasse et al, 2017;Silberberger et al, 2016).…”

“…The strength, width, and depth of the NCC varies seasonally as it is partly driven by run-off from land (Silberberger, 2017). Coastal regions, shallow banks, and cross-shelf troughs represent the three landscape elements that characterize the region and differ with respect to depth and hydrography (Eiane et al, 2018;Silberberger et al, 2016). Water of the NCC (salinity <34.5) characterizes the relatively shallow coastal region (<50 m depth), which remains mixed for most time of the year.…”

“…in mesozooplankton biomass during spring and summer (Aarflot et al, 2018;Arashkevich et al, 2002). The life cycle of Calanus, however, involves a descent away from surface waters to deep overwintering habitats from late summer to spring (Kaartvedt, 2000), while a diverse mesozooplankton community remains within the productive surface water throughout most of the year (Eiane et al, 2018;Silberberger et al, 2016). Consequently, a variety of planktonic groups may have an important ecosystem function (Hansen et al, 1999;Pasternak et al, 2008).…”

“…This study also reported that meroplankton rarely contributed with more than 10% to the total zooplankton abundance, with an annual average contribution of 2%-4%. While the abundance and the seasonal pattern of the numerically dominant holoplankton taxa and cod larvae was similar in 1949/1950 and 2013/2014 (Eiane et al, 2018;Wiborg, 1954), meroplankton has become a more abundant component of the zooplankton community (Silberberger et al, 2016). In 2013/2014, the annual average contribution of meroplankton to the mesozooplankton abundance was approximately 20% closer to the coast and around 5% over the central shelf (Eiane et al, 2018;Silberberger et al, 2016).…”