Variation of phytoplankton assemblages of Kongsfjorden in early autumn 2012: a microscopic and pigment ratio-based assessment

Abstract

Phytoplankton species distribution and composition were determined by using microscopy and pigment ratios in the Kongsfjorden during early autumn 2012. Variation in sea surface temperature (SST) was minimal and matched well with satellite-derived SST. Nutrients were generally limited. Surface phytoplankton abundance ranged from 0.21 × 10(3) to 10.28 × 10(3) cells L(-1). Phytoplankton abundance decreased with depth and did not show any significant correlation with chlorophyll a (chl a). Column-integrated phytoplankton cell counts (PCC) ranged from 94.3 × 10(6) cells m(-2) (Kf4) to 13.7 × 10(6) cells m(-2) (Kf5), while chl a was lowest at inner part of the fjord (6.3 mg m(-2)) and highest towards the mouth (24.83 mg m(-2)). Biomass from prymnesiophytes and raphidophytes dominated at surface and 10 m, respectively. The contribution of Bacillariophyceae to biomass was low. Generally, heterotrophic dinoflagellates were great in abundance (12.82 %) and ubiquitous in nature and were major contributors to biomass. Various chl pigments (chl b, chl c, phaeopigments (phaeo)) were measured to obtain pigment/chl a ratios to ascertain phytoplankton composition. Phaeo were observed only in inner fjord. Chl b:a ratios and microscopic observations indicated dominance of Chlorophyceae at greater depths than surface. Furthermore, microscopic observations confirmed dominance of chl c containing algae throughout the fjord. The study indicates that pigment ratios can be used as a tool for preliminary identification of major phytoplankton groups. However, under the presence of a large number of heterotrophic dinoflagellates such as Gymnodinium sp. and Gyrodinium sp., pigment signatures need to be supplemented by microscopic observations.

Spatial and seasonal variations of dinoflagellates and ciliates in the Kongsfjorden, Svalbard

“…This creates a natural variability from freshwater to marine and vice versa within the Kongsfjord, thereby creating a natural environment for more eurythermal species to thrive within the fjord. Nevertheless, in the present study, hydrography of the sampling stations clearly showed the presence of SW and intermediate waters in the top 40 m while AW were found below 75 m in both seasons (Bhaskar et al, 2016; David & Krishnan, 2017). Since the sampling depths were restricted to top 20 m, the role of subsurface AW in the distribution of the dinoflagellates and ciliates is minimal.…”

“…In order for better comparison between the two seasons, sampling for microscopy samples was restricted to top 20 m in this study. Detailed description about the variations in hydrography has been discussed previously (Bhaskar et al, 2016; David & Krishnan, 2017); however, a brief description of the hydrography is given here.…”

“…Variable stratification was observed in the top 16 m water column throughout the transect. Strongly stratified surface waters (SW) were restricted to KF4 and KF5 due to glacial meltwater in both seasons (Bhaskar et al, 2016; David & Krishnan, 2017).…”

“…Silicate (SiO 4 ) could not be estimated during summer and in fall the depth average concentration of SiO 4 was >1 μM in all stations (Table 2). Also, during fall, mean nitrate to phosphate ratio (N:P) ranged from 1.69 at KF2 to 4.35 at KF5, whereas mean NO 3 to SiO 4 ratio (N:Si) was >1 only at KF5 (Bhaskar et al, 2016).…”

“…Chl a was measured by HPLC (summer 2011) and spectrophotometrically (fall 2012) for surface, 10 m and 20 m depth. Bhaskar, Tripathy, Sabu, Laluraj, and Rajan (2016) and Krishnan, Sinha, and Atri (2012) describe the detailed methodology used for chl a analysis. The depth‐integrated values were calculated using the trapezoidal method.…”