Abstract
Microzooplankton community structure, distribution, growth and herbivory were examined in the eastern Fram Strait and Arctic Ocean shelf affected by the Atlantic water inflow in May (during the spring bloom, chlorophyll up to 9 µg l-1) and August (post-bloom, 0.13 – 1.7 µg l-1) 2014. Microzooplankton were collected along two longitudinal transects at 79°N and 79.4 °N from the slope to the ice edge and crossed the Western Spitsbergen Current (WSC). In May, integrated microzooplankton biomass in the upper 100 m ranged from 0.16 g C m-2 above the slope to 2.3 g C m-2 within WSC (0.71 g C m-2 on average). Mixotrophic oligotrich ciliates from the genus Strombidium dominated in the spring and formed a surface bloom (79 x 103 cells L-1, 206 µg C L-1). This is the largest microzooplankton biomass recorded in the Arctic so far. The heterotrophic dinoflagellates Gyrodinium and Protoperidinium were abundant at the diatom-dominated stations in the marginal ice zone. In the summer, a more diverse community included a large proportion of heterotrophic and mixotrophic dinoflagellates, tintinnids, and other ciliates. Microzooplankton biomass increased to the average of 1.27 g C m-2. At the ice-covered and open water stations in the Yermak shelf and deep basin, microzooplankton grew at 0.04 to 0.38 d-1; their species-specific growth rates were up to 1.79 d-1. Microzooplankton herbivory on average removed 72% (36 to >100%) of daily primary production with the exception of Phaeocystis pouchetii colonies. These results indicate that the microbial food web plays a central role in the carbon cycle in this Atlantic-influenced polar system.
Highlights
Rapid warming is occurring in the Arctic (IPCC, 2013), where average temperatures have risen twice as fast as those elsewhere in the world (Corell, 2006)
Samples were collected from different depths: 2, 5, 10, 20, 30, 40, 50, 100 m and the deep chlorophyll layer (DCL) using Niskin bottles mounted on a rosette
Microzooplankton biomass in the upper 100 m of Transit D was distributed unequally along the transect (Figures 2B, 3B). It was elevated in the mixed layer at D1 and D3, and reached its maximum for the whole study period at D5 (2306 mg C m−2) mostly due to the mixotrophic oligotrich ciliates Strombidium sp. (71000 cells L−1) and S. conicum (8000 cells L−1), which formed nearly 90% of total ciliate biomass (206 μg C L−1) near the surface (Figure 2C)
Summary
Rapid warming is occurring in the Arctic (IPCC, 2013), where average temperatures have risen twice as fast as those elsewhere in the world (Corell, 2006). The warming trend has resulted in widespread reductions in Arctic ice cover (Kwok and Rothrock, 2009). Sea ice is the central component of the polar environment and its alternations translate global warming to marine ecosystems, including changes in biological productivity, food web structure, and the biogeochemical cycles (Wassmann and Reigstad, 2011; Wassmann and Lenton, 2012). Polar Microzooplankton Distribution and Dynamics open-water period in the Arctic Ocean is projected to boost pelagic primary production (Slagstad et al, 2011; Brown and Arrigo, 2012) and increase the role of small-sized phytoplankton (Li et al, 2009). The non-linear nature of ecosystem response to climate change complicates predictions. Understanding and predicting its effects at the system level requires insight into the coupled nature of physical and biological interactions
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