Decline in plankton diversity and carbon flux with reduced sea ice extent along the Western Antarctic Peninsula

Abstract

Since the middle of the past century, the Western Antarctic Peninsula has warmed rapidly with a significant loss of sea ice but the impacts on plankton biodiversity and carbon cycling remain an open question. Here, using a 5-year dataset of eukaryotic plankton DNA metabarcoding, we assess changes in biodiversity and net community production in this region. Our results show that sea-ice extent is a dominant factor influencing eukaryotic plankton community composition, biodiversity, and net community production. Species richness and evenness decline with an increase in sea surface temperature (SST). In regions with low SST and shallow mixed layers, the community was dominated by a diverse assemblage of diatoms and dinoflagellates. Conversely, less diverse plankton assemblages were observed in waters with higher SST and/or deep mixed layers when sea ice extent was lower. A genetic programming machine-learning model explained up to 80% of the net community production variability at the Western Antarctic Peninsula. Among the biological explanatory variables, the sea-ice environment associated plankton assemblage is the best predictor of net community production. We conclude that eukaryotic plankton diversity and carbon cycling at the Western Antarctic Peninsula are strongly linked to sea-ice conditions.

Diversity of Microbial Eukaryotes Along the West Antarctic Peninsula in Austral Spring

“…Overall, the diversity (richness and Chao1 index; Supplementary Figure 2A ), assessed using 18S rRNA, was comparable to what was previously reported in other parts of the world ocean ( de Vargas et al, 2015 ) and in the same region in other periods of the year ( Lin et al, 2021 ). As noted previously, the spring corresponds to a low abundance of protists ( Trefault et al, 2021 ), although, Arrigo et al (2017) reported some areas of relatively high chlorophyll in early spring.…”

“…Overall, the mixed layer was deeper than the chlorophyl maximum depth across the cruise, explaining the relative similarity between the samples taken at the sub-surface and at the DCM layer regarding both environmental parameters and planktonic community ( Table 1 and Figures 1B,C ). As noted above, reduced sea ice has been identified as a good predictor of net community production ( Lin et al, 2021 ). The decrease in coverage and duration of sea ice observed prior to 2008 reversed temporarily and began increasing ( Ducklow et al, 2013 ; Schofield et al, 2018 ).…”

“…The late spring/early summer period of the year in this area still has a considerable amount of sea ice, which limits the ability to a sample. Consequently, most of the studies focusing on the microbial eukaryotes in the Southern Ocean, including phytoplankton, were carried out during the January-April (summer/autumn) period when more open water and light availability have already produced the annual phytoplankton bloom ( Flaviani et al, 2018 ; Clarke et al, 2019 ; Christaki et al, 2021 ; Lin et al, 2021 ). However, phytoplankton dynamics and environmental factors affecting them were examined by Arrigo et al (2017) in early spring during the beginning of the bloom period.…”

“…During the recent decades, the ice cover of Antarctica has changed dramatically due to climate change ( Martinson et al, 2008 ; Comiso et al, 2017 ; Schofield et al, 2018 ; Clem et al, 2020 ), with a total increase of 3°C since 1951 and an anthropogenic impact that is not yet clear ( Whitehouse et al, 2008 ; Ducklow et al, 2012 ; Turner et al, 2016 ). These changes in ice cover resulted in a release of nutrients and modification of the salinity in the area ( Moline et al, 2004 ), potentially impacting the Antarctic ecosystem, as well as influencing the global climate ( Cavanagh et al, 2021 ; Lin et al, 2021 ). Within the Southern Ocean, the West Antarctic Peninsula (WAP) is in itself unique, as three circumpolar Antarctic marine ecosystems: the Permanently Open Ocean Zone, the Seasonal Ice Zone, and the Coastal and Continental Shelf Zone, converge ( Tréguer and Jacques, 1992 ) and result in strong environmental gradients that may affect diversity.…”

“…Moreover, they can be heterotrophs (nano- and microzooplankton), phototrophs (phytoplankton), and mixotrophs/“mixoplankton” (combining phagotrophy and phototrophy; Stoecker et al, 2016 ; Leles et al, 2018 ; Ward, 2019 ). While an increasing number of studies have looked at the composition of the protists in marine systems, some areas are still notably understudied, including the polar regions ( de Vargas et al, 2015 ; Pernice et al, 2015 ; Lin et al, 2021 ).…”