Ultra-algae (<5 pm) in the ice, at the ice-water interface and in the under-ice water column (southeastern Hudson Bay, Canada)

Abstract

In ice-covered southeastern Hudson Bay (Canada), the plume of the Great Whale River determines onshore-offshore gradients in salinity, concentrations of suspended particles and of dissolved nutrients, and stratification of the water column. Because of the snow and ice cover, irradiance in the water column is low, and it is further attenuated by the turbidity of water in the plume. Ultraalgae (0.4 to 5 pm) were found primarily in the sea-ice bottom, and they also occurred at the ice-water interface and in the water column. This is the first time such algae have been directly observed in the sea-ice environment. Concentrations ranged between 36 X 103 and 63 X 106 cells I-', and the contribution to total chlorophyll a varied from 9 to 96%. Concentrations of ultra-algae in this subarctic environment and their contribution to total algal biomass were much higher than previously hypothesized for high-latitude marine waters. Ultra-algal abundances varied primarily w~t h depth, but also with distance from shore and with time. The ice bottom, the ice-water interface and the water column formed distinct habitats, which were colonized by different taxonomic assemblages. These comprised chlorophyll-rich eucaryotes (35 to 93 %), procaryotic cyanobacteria (phycoerythrin-rich, 2 to 51 %; and phycocyanin-rich, 4 to 24 %) and eucaryote cryptomonads (0 to 6 % ) . Eucaryotes were dominant in the ice bottom and at the ice-water interface. Their importance increased with distance from shore, following the onshore-offshore salinity gradient. Procaryotes dominated in the water column near the mouth of the river. Total abundances were well correlated with salinity at the bottom of the ice (which determined ice structure), and with light attenuation at the ice-water interface and in the water column (which reflected particle load). It is concluded that the main factor controlling ultra-algal abundances. in the studied environment, is the availability of solid substratum (i.e. ice structure and particle load).

Phototrophic and heterotrophic nano- and microorganisms of sea ice and sub-ice water in Guba Chupa (Chupa Inlet), White Sea, in April 2002

“…Very high concentrations of phototrophic picoalgae (eukaryotic cells of about 1.5 µm) should probably not be considered as unique to the White Sea. Similar cells, albeit at lower abundance (36 × 10 3 cells l -1 and 63 × 10 3 cells l -1 ), were found in ice and in subice water near the Canadian coast (Robineau et al 1994) and in the Chukchi Sea (10 3 -10 4 cells ml -1 ; Fig. 4.…”

Small phytoplankton contribution to the standing stocks and the total primary production in the Amundsen Sea

“…After 4-5 h incubations, the incubated waters were well mixed and distributed into two filtration sets for the carbon and nitrogen uptake rates of total (> 0.7 µm) and small-sized cells (0.7-5 µm). Small-sized cells are generally defined as small phytoplankton in comparison to large diatoms (> 5 µm) (Robineau et al, 1994; references therein). The incubated waters (0.3 L) for total uptake rates were filtered through pre-combusted GF/F filters (25 mm diameter), whereas waters samples (0.5 L) for the uptake rates of small phytoplankton were passed through 5 µm Nuclepore filters (47 mm) to remove large phytoplankton cells (> 5 µm) and then the filtrate was passed through pre-combusted GF/F (25 mm) for the small phytoplankton (Lee et al, 2013).…”

Protists in Arctic drift and land‐fast sea ice

“…Smaller species are rarely investigated even though their contribution to biomass in the ice can reach up to 45% (Robineau et al. , Guglielmo et al. , Stoecker et al.…”