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

• Published in: Marine ecology. Progress series (Halstenbek) 1994, Vol.115 (1/2), p.169-180
• Main Authors: Robineau, Brigitte, Legendre, Louis, Therriault, Jean-Claude, Fortier, Louis, Rosenberg, Gene, Demers, Serge
• Format: Article
• Language: English
• Subjects: Chlorophylls; Cyanobacteria; Ice; Irradiance; Marine; Oceans; Plankton; River water; Salinity; Sea water; Surface water
• ISSN: 0171-8630; 1616-1599
• DOI: 10.3354/meps115169

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 μm) 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 × 103 and 63 × 106 cells l−1, 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 with 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).