Annual patterns in phytoplankton phenology in Antarctic coastal waters explained by environmental drivers

Abstract

Coastal zones of Antarctica harbor rich but highly variable phytoplankton communities. The mechanisms that control the dynamics of these communities are not well defined. Here we elucidate the mechanisms that drive seasonal species succession, based on algal photophysiological characteristics and environmental factors. For this, phytoplankton community structure together with oceanographic parameters was studied over a 5-year period (2012-2017) at Rothera Station at Ryder Bay (Western Antarctic Peninsula). Algal pigment patterns and photophysiological studies based on fluorescence analyses were combined with data from the Rothera Time-Series program. Considerable interannual variation was observed, related to variations in wind-mixing, ice cover and an El Niño event. Clear patterns in the succession of algal classes became manifest when combining the data collected over the five successive years. In spring, autotrophic flagellates with a high light affinity were the first to profit from increasing light and sea ice melt. These algae most likely originated from sea-ice communities, stressing the role of sea ice as a seeding vector for the spring bloom. Diatoms became dominant towards summer in more stratified and warmer surface waters. These communities displayed significantly lower photoflexibility than spring communities. There are strong indications for mixotrophy in cryptophytes, which would explain much of their apparently random occurrence. Climate models predict continuing retreat of Antarctic sea-ice during the course of this century. For the near-future we predict that the marginal sea-ice zone will still harbor significant communities of haptophytes and chlorophytes, whereas increasing temperatures will mainly be beneficial for diatoms.

Viral lysis modifies seasonal phytoplankton dynamics and carbon flow in the Southern Ocean

“…Finally, they were succeeded by diatoms Phyto IX during late summer and austral fall (mid-February to March) when light availability and nutrient (phosphate and nitrate) concentrations declined as a result of shorter daylengths, increased light attenuation and biological nutrient uptake [ 36 ]. Although we did not specifically identify the species of diatoms during the season, van Leeuwe et al [ 53 ] observed relatively high numbers of Thalassiosira sp. (5–20 µm cell length) and Chaetoceros sp.…”

Annual phytoplankton dynamics in coastal waters from Fildes Bay, Western Antarctic Peninsula

“…in the WAP has been studied before 8,9 , but many of these studies relied on optical microscopy and pigment analysis 10,[37][38][39] and focused only on the summer period [40][41][42] . Metabarcoding characterization in the WAP has been performed for samples from the PAL-TER, Fildes Bay (King George Island) and the RaTS [43][44][45] .…”

Annual phytoplankton dynamics in coastal waters from Fildes Bay, Western Antarctic Peninsula

“…Phytoplankton composition in the WAP has been studied before (Kopczynska 2008;Lange et al 2018), but many of these studies relied on optical microscopy and pigment analysis (Biggs et al 2019;Leeuwe et al 2020;Rozema et al 2016;Wasilowska et al 2015) and focused only on the summer period (Annett et al 2010;Garibotti et al 2003;Lima et al 2019). Metabarcoding characterization in the WAP has been performed for samples from the PAL-TER, Fildes Bay (King George Island) and the RaTS (Luo et al 2016; 11/58 Luria et al 2014;Rozema et al 2017).…”