AUTHOR=Lampe Vanessa , Nöthig Eva-Maria , Schartau Markus 

TITLE=Spatio-Temporal Variations in Community Size Structure of Arctic Protist Plankton in the Fram Strait

JOURNAL=Frontiers in Marine Science

VOLUME=Volume 7 - 2020

YEAR=2021

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2020.579880

DOI=10.3389/fmars.2020.579880

ISSN=2296-7745

ABSTRACT=3 The Arctic Ocean is subject to severe environmental changes, including the massive decline
4 in sea ice due to continuous warming in many regions. Along with these changes, the Arctic
5 Ocean’s ecosystem is affected on various scales. The pelagic microbial food web of the Arctic is
6 of particular interest, because it determines mass transfer to higher trophic levels. In this regard,
7 variations in the size structure of the microbial community reflect changes in size-dependent
8 bottom-up and top-down processes. Here we present analyses of microscopic data that resolve
9 details on composition and cell size of unicellular plankton, based on samples collected between
10 2016 and 2018 in the Fram Strait. Using the Kernel Density Estimation method, we derived
11 continuous size spectra (from 1 μm to ≈ 200 μm Equivalent Spherical Diameter, ESD) of cell
12 abundance and biovolume. Specific size intervals (3–4, 8–10, 25–40, and 70–100μm ESD)
13 indicate size-selective predation as well as omnivory. In-between size ranges include loopholes
14 with elevated cell abundance. By considering remote sensing data we could discriminate between
15 polar Arctic- and Atlantic water within the Fram Strait and could relate our size spectra to
16 the seasonal change in chlorophyll-a concentration. Our size spectra disclose the decline in
17 total biovolume from summer to autumn. In October the phytoplankton biovolume size-spectra
18 reveal a clear relative shift towards larger cell sizes (> 30 μm). Our analysis highlights details in
19 size spectra that may help refining allometric relationships and predator-prey dependencies for
20 size-based plankton ecosystem model applications.