Shifts in the dominance between diatoms and cryptophytes during three late summers in the Bransfield Strait (Antarctic Peninsula)

Influence of oceanographic features on spatial and interannual variability of phytoplankton in the Bransfield Strait, Antarctica

“…Picoplankton contribution was unlikely to have had any major importance during the sampling periods, as these very small forms are generally not a relevant component within the Southern Ocean (Scott and Marchant, 2005), although within the oligotrophic Pacific Antarctic sector this fraction was estimated as 7-33% of the total phytoplankton biomass (Wright et al, 2009). In our work, a pronounced relative contribution of cryptophytes was primarily associated with lower Chl-a (b 1 mg m − 3 ), contrasting other studies that have reported a high abundance of cryptophytes in association with higher Chl-a (N 1 mg m − 3 ) at other sites across the BS or in adjacent regions (Mendes et al, 2013;Moline and Prézelin, 1996;Moline et al, 2004;Rodriguez et al, 2002). Moreover, there were noteworthy differences in phytoplankton composition between firstly ; gray bars), temperature (SST, in°C; dash-dot-dash line) and AMSR-E sea ice area (10 2 km 2 ; dotted line), calculated as the synoptic mean in the white box shown in Fig.…”

“…Apart from this, as silicate is not required for cryptophyte growth, the relationship between these organisms and the concentration of silicate was positive in 2004, when those flagellates were numerically prominent. This pattern of association (high silicate levels and predominance of cryptophytes) was also emphasized in the late summer of 2010 in the region (Mendes et al, 2013). Relatively high factor loadings were also obtained for the UMLD and water column stability, which together with the high factor loadings displayed by temperature, salinity and Chl-a confirm the strong influence of the water column physical structure on phytoplankton variability as previously noted by several sources (Mitchell and Holm-Hansen, 1991;Ryabov et al, 2010).…”

“…In addition, El Niño-Southern Oscillation (ENSO) can also influence phytoplankton composition, by impacting on the amount of sea ice, which triggers phytoplankton species variability (Stammerjohn et al, 2008;Yuan, 2004). For instance, ENSO-influenced factors have been suggested to favor cryptophytes as major contributors to the total chlorophyll-a biomass in the summer of 2010 at some sites in the BS (Mendes et al, 2013). During El Niño events, a decrease in northwestern winds results in a/the northward displacement of the Antarctic Circumpolar Current Front and intensification of the Weddell Gyre, allowing Weddell Sea water to flow into the eastern sector of the BS (Loeb et al, 2010).…”

“…Nevertheless, several studies have highlighted the increasing importance of cryptophytes in the AP as they prevail over diatoms, particularly within ice melting regions (Moline and Prézelin, 1996;Moline et al, 2004). Several other studies have related the seasonal succession of phytoplankton along the west of the AP (wAP) to the timing of the sea ice retreat, particularly from the south of Gerlache Strait to Marguerite Bay (Garibotti et al, 2005;Prézelin et al, 2000), with some evidence found within the BS (Mendes et al, 2013;Varela et al, 2002). Firstly, diatom blooms attain higher biomass when the sea ice retreat is under way and, with a continued stratification, cryptophytes can numerically replace these diatoms (Ducklow et al, 2007).…”

Phytoplankton community structure in relation to vertical stratification along a north‐south gradient in the Northeast Atlantic Ocean

“…Another main PFT, the diatoms, were distinguished by their association with the surface layers of non-stratified waters (N 2 < 2 3 10 25 rad 2 s 22 ), colder water temperatures, higher nutrient concentrations and higher potential for light limitation. There is some evidence for successional shifts in dominance between diatoms and cryptophytes (Moline et al 2004;Mendes et al 2013) and several studies have reported selective grazing by different zooplankton species on either diatoms or cryptophytes (Cotonnec et al 2001;Haberman et al 2003;Liu et al 2010), which may advocate for an additional PFT for cryptophytes. If warranted, our analysis suggests that this cryptophyte PFT can be distinguished from diatoms by the closer association of cryptophytes with high Z m /Z eu and conversely of diatoms with high Z eu PO 4 .…”