Shifts in coastal Antarctic marine microbial communities during and after melt water-related surface stratification

Abstract

Antarctic coastal waters undergo major physical alterations during summer. Increased temperatures induce sea-ice melting and glacial melt water input, leading to strong stratification of the upper water column. We investigated the composition of micro-eukaryotic and bacterial communities in Ryder Bay, Antarctic Peninsula, during and after summertime melt water stratification, applying community fingerprinting (denaturing gradient gel electrophoresis) and sequencing analysis of partial 18S and 16S rRNA genes. Community fingerprinting of the eukaryotic community revealed two major patterns, coinciding with a period of melt water stratification, followed by a period characterized by regular wind-induced breakdown of surface stratification. During the first stratified period, we observed depth-related differences in eukaryotic fingerprints while differences in bacterial fingerprints were weak. Wind-induced breakdown of the melt water layer caused a shift in the eukaryotic community from an Actinocyclus sp.- to a Thalassiosira sp.-dominated community. In addition, a distinct transition in the bacterial community was found, but with a few days' delay, suggesting a response to the changes in the eukaryotic community rather than to the mixing event itself. Sequence analysis revealed a shift from an Alpha- and Gammaproteobacteria to a Cytophaga-Flavobacterium-Bacteroides-dominated community under mixed conditions. Our results show that melt water stratification and the transition to nonstabilized Antarctic surface waters may have an impact not only on micro-eukaryotic but also bacterial community composition.

Changes in Marine Prokaryote Composition with Season and Depth Over an Arctic Polar Year

“…Consequently, Bacteroidetes and phytoplankton are often found in close association in polar waters (Grossart et al, 2005;Piquet et al, 2011;Williams et al, 2013) with the relative abundance of the former significantly correlated with the emergence of the late spring blooms (Alonso-Sáez et al, 2008). During May of 2014, the Flavobacteriaceae were notable by their prolific increase in relative abundance from negligible levels in March, congruent with the spike in chloroplast 16S rRNA abundance (Figure 5) and chl a maxima ( Table 1).…”

“…Proteorhodopsins, which support photoheterotrophic growth, have however been found in flavobacterial isolates (Gómez-Consarnau et al, 2007) previously and this may explain the peak abundance observed during the higher photoirradiance conditions of May. It has been suggested that increased numbers of Bacteroidetes would be found in the water column during spring and summer as a consequence of increased melting sea ice, either by seeding, as persistent members of sea ice biota (Bowman et al, 2012;Lo Giudice et al, 2012) or as a result of growth on organic matter released by the thawing (Piquet et al, 2011). As an abundance of Flavobacteriial proteins involved in oxidative stress protection have also been recovered from Antarctic metaproteomes, this suggests that the group may also exhibit a higher tolerance to the high solar irradiance found in polar spring and summer waters (Williams et al, 2013) and may indeed come to play a more dominant role in the surface layers of an ice-free Arctic.…”

On the phytoplankton bloom in coastal waters of southern King George Island (Antarctica) in January 2010: An exceptional feature?

“…Hence, here we hypothesize that heterotrophic dinoflagellates, which represent a large part of Antarctic microzooplankton biomass, can be responsible for significant losses of daily primary production. The results of Price and Steinberg (2013) suggest that microzooplankton may usually control the start of blooms in areas like coastal KGI, when Chl a values are low (i.e., , 0.5 mg m 23 ; Sherr and Sherr 2009) and substantially contribute to their decay (Calbet and Landry 2004). However, phytoplankton blooms are normal features in many other coastal Antarctic areas, and this can be attributed to the generally low growth rates of heterotrophic protists in cold waters, compared with phytoplankton (Rose and Caron 2007), resulting in uncoupled grazing activity of microzooplankton regarding phytoplankton growth rates.…”

“…Significant interannual climate variability in sea ice extension and ocean surface temperatures along the WAP has been associated with the Southern Annular Mode (SAM) and the El Niñ o Southern Oscillation (ENSO; Meredith et al 2008;Schloss et al 2012). Climate warming is supposed to induce important changes in polar ecosystems, from microbial communities (Piquet et al 2011) to apex predators' levels (Trathan et al 2007). Phytoplankton is at the base of the food web so that changes affecting primary production dynamics affect organisms of higher trophic levels.…”

Springtime phytoplankton dynamics in Arctic Krossfjorden and Kongsfjorden (Spitsbergen) as a function of glacier proximity

“…2) showing a homogeneous water column for the upper 60 m at the O and M stations. The resultant vertical redistribution of phytoplankton biomass may have interrupted bloom formation, and could cause changes in phytoplankton composition, as found before (Piquet et al, 2011;Hegseth and Tverberg, 2013). After the wind event, a period characterized by relatively calm southerly winds permitted stabilization of the water column and therefore biomass buildup.…”