Cryptophyte and Photosynthetic Picoeukaryote Abundances in the Bransfield Strait during Austral Summer

An-Yi Tsai,Eugene Morozov,Alexander Polukhin,Evgeny Sakhon,Vladimir Mukhanov,Vladimir Artemiev

doi:10.3390/w14020185

Abstract

A remarkable shift in the species composition and size distribution of the phytoplankton community have been observed in coastal waters along the Antarctic Peninsula over the last three decades. Smaller photoautotrophs such as cryptophytes are becoming more abundant and important for the regional ecosystems. In this study, flow cytometry was used to quantify the smallest phytoplankton in the central Bransfield Strait and explore their distribution across the strait in relation to physical and chemical properties of the two major water masses: the warmer and less saline Transitional Zonal Water with Bellingshausen Sea influence (TBW), and the cold and salty Transitional Zonal Water with Weddell Sea influence (TWW). Pico- and nano-phytoplankton clusters were distinguished and enumerated in the cytograms: photosynthetic picoeukaryotes, cryptophytes (about 9 µm in size), and smaller (3 µm) nanophytoplankton. It was shown that nanophytoplankton developed higher abundances and biomasses in the warmer and less saline TBW. This biotope was characterized by a more diverse community with a pronounced dominance of Cryptophyta in terms of biomass. The results support the hypothesis that increasing melt-water input can potentially support spatial and temporal extent of cryptophytes. The replacement of large diatoms with small cryptophytes leads to a significant shift in trophic processes in favor of the consumers such as salps, which able to graze on smaller prey.

Highlights

Diatoms, haptophytes, and cryptophytes represent the major taxonomic groups of phytoplankton in the Southern Ocean [1,2,3,4,5]
We used flow cytometry (FCM) to enumerate the smallest known component of the phytoplankton community, picophytoplankton (0.2 to 2.0 μm size fraction), which are recognized as an important player in the Southern Ocean ecosystem. In this part of the work, we focused on revealing spatial patterns of picophytoplankton abundance in relation to the water masses and frontal zones in the Bransfield Strait as the frontal features are among the factors other than temperature that control the abundance and distribution of phytoplankton
Vertical distribution of water temperature and salinity across the Bransfield Strait (BS) (Figure 4) corresponded to the typical BS circulation system, with the Southern BS Current carrying waters advected from the Weddell Sea and meeting the relatively warm and less saline waters from the western Antarctic Peninsula through the Gerlache Strait Current at the western end of the BS [35,36]

Summary

Introduction

Haptophytes (predominantly Phaeocystis antarctica), and cryptophytes represent the major taxonomic groups of phytoplankton in the Southern Ocean [1,2,3,4,5]. Summer phytoplankton blooms in coastal waters of the Antarctic Peninsula are usually associated with a shallow upper mixed layer (UML) that keeps phytoplankton under favorable light conditions and better supply of dissolved iron (e.g., [6]). Diatoms and/or P. antarctica make the largest contribution to the blooms, but the role of cryptophytes has been reported to substantially increase, especially in water areas of melting glaciers [7,8,9]. Available data provide evidence of the transformation of the Antarctic phytoplankton community as a probable consequence of global warming [10]. A decrease in the food supply of krill and a substitution of the latter by other zooplankton (such as salps) imply a reduction in the carbon pool available for higher trophic levels by almost 70% [12]

Methods

Results

Discussion

Conclusion