Temporal and spatial variation of phytoplankton in Admiralty Bay, South Shetlands: the dynamics of summer blooms shown by pigment and light microscopy analysis

Abstract

We conducted an integrated study of phytoplankton taxonomic composition, biomass and physicochemical properties of the water in Admiralty Bay, South Shetlands. The aim of the study was to provide detailed information on phytoplankton composition and diversity related to relevant environmental conditions. High-performance liquid chromatography pigment analysis and microscopy were performed in the summers of 2007 and 2009-2010. Results for 2007 showed a typical high-nutrient, low-chlorophyll system. Total carbon biomass and cell numbers were dominated by nanoflagellates, while diatoms made up 1.2-4.5 % of the total algal numbers and contributed a maximum of 23.4 % to the total cell carbon. A small algal bloom occurred in the center of the bay, with chlorophyll a values of *1.0 lg l -1 . The prevalent pigment was 19 0 -hexanoyloxyfucoxanthin, characteristic of the Prymnesiophyceae. In January 2010, the values of chlorophyll a (8-24 lg l -1 ) and cell carbon (150 lg l -1 ) were the highest ever recorded for Admiralty Bay. In general the algal populations were dominated numerically by nanoflagellates, but a bloom of diatoms (maximum 30 % of total cells and 50 % of total cell carbon) was observed. Diatoms were dominated by those of micro-size: Thalassiosira ritscheri and T. antarctica. The dominant pigment was fucoxanthin, mainly found in diatoms. The diatom bloom could be related to the southeast wind direction, stable water column conditions and an inflow of diatom-rich waters from the Bransfield Strait, while the input of high-turbidity, low-salinity water from melting glaciers and strong katabatic northwest winds could favor nanoflagellates.

Abiotic Changes Driving Microphytoplankton Functional Diversity in Admiralty Bay, King George Island (Antarctica)

“…Marguerite Bay (sector 10) experienced a significant decrease in total biomass over the past 15 years (Rozema et al, 2017), due to increases in temperature (Boyce et al, 2010;Schloss et al, 2014). The chlorophyll a data of the present study follow this trend for some regions of WAP (Table 3), with values around 0.5-2.0 mg.m −3 (Lange et al, 2007;Wasiłowska et al, 2015). Exceptions were in cases of blooms (e.g., Wasiłowska et al, 2015 sector 1;Schloss et al, 2014 sector 2;Lange et al, 2018 sector 2;Aracena et al, 2018 sector 3; Table 3).…”

“…It should be noted that although the phytoplankton community and events of Antarctic blooms are commonly dominated by diatoms, other taxa are also important components of the trophic web (Henley et al, 2019). Increases in cryptophytes and other flagellates have previously been reported (e.g., Phaeocystis antarctica and Gymnodiniales), as well as the substitution of diatoms for these flagellates in WAP, due to the influence of sea ice melt (Moline et al, 2004;Mendes et al, 2013;Lange et al, 2014;Mendes et al, 2017), as observed in the WAP sectors of the present study (Figure 3): sector 1 (Wasiłowska et al, 2015), sector 4 (Mendes et al, 2012(Mendes et al, , 2013, oceanic regions of sectors 5 (Mar de Weddell) and 6 (Passagem de Drake) (Mendes et al, 2012), as well as sectors 7 (Mendes et al, 2018), 9 (Gerlache Strait) (Mendes et al, 2017;Russo et al, 2018) and 11 (Arrigo et al, 2017).…”

“…In this context, Mendes et al (2018) found lower values for salinity (mean 33.68) in areas near ice-covered regions and higher values (mean 34.14) in regions with little or no influence of ice cover seasonality for sector 7 (Weddel-Scotia Confluence Zone), thus correlating low salinity with water column stability. Additionally, Wasiłowska et al (2015) associated low salinities (<34) with increased water column stability and a shallow (<2 m) mixture layer in sector 1. Similarly, Mendes et al (2017) related high values of salinity with reduced water column stability and, consequently, the presence of a deeper mixing layer in sector 9 (Gerlache Strait).…”

“…Otherwise, centric diatoms (Thalassiosira spp. and Corethron pennatum) observed in scenario ii, without sea ice melt, were possibly transported by currents from Bransfield strait (Kopczyńska, 2008;Wasiłowska et al, 2015).…”

Variabilidad espacio-temporal del fitoplancton de la ensenada Mackellar, Bahía Almirantazgo, Isla Rey Jorge, Antártida, durante el verano austral 2012/2013

“…En particular, los estudios relacionados con la composición del fitoplancton en el sur de las Islas Shetland y los alrededores de la PA han sido relativamente abundantes (García-Muñoz et al 2013). Recientemente en la bahía Almirantazgo se ha reportado una dominancia de nanoflagelados en número y biomasa sobre diatomeas del microplancton, en las cercanías de la zona costera de la estación Polaca Henryk Arctowski, donde se encontró una tendencia de disminución de dichas diatomeas en la contribución total, de 44% entre 1996-1998 a 5% entre 2003-2005(Wasilowska et al 2015. Adicionalmente, Vanzan et al (2015) mostraron una alternancia estacional entre nanoplancton y picoplancton asociado al sistema de corrientes de mesoescala y el pastoreo estacional, donde sugieren que a futuro se debe desarrollar trabajos para comunidades < 20 µm para estudiar los efectos en la trama trófica microbiana y sus posibles efectos ambientales en altos niveles tróficos de las zonas costeras de la bahía Almirantazgo.…”