Horizontal distribution of sea-ice microalgae:environmental control and spatial processes (southeastern Hudson Bay, Canada)

Abstract

Microalgae from the ice bottom and the ice-water interface were collected in southeastern Hudson Bay (Canada) along inshore-offshore transects during April and May 1989 and 1990. The transects extended from the mouth of the Grande riviere d e la Baleine (Great Whale River; almost fresh waters) to 25 km offshore (saline waters). Salinity and nutrients at the ice-water interface exhibited marked horizontal gradients which were more pronounced In 1990 than in 1989 Algal concentrations as well as species diversity and evenness also presented hor~zontal structures. Canonical Correspondence Analyses (CCA) showed that a large part of the var~ation in specles abundances (i.e. 4 3 to 50%] could be explained by environmental variables, especially salinity. Given the spatial structure of salinity, Partial CCA were used to assess the direct relationships between environmental variables and algae, independent of purely spa t~a l processes. In 1990 (strong inshore-offshore g rad~en t ) , most of the effect of salinity on algal abundances reflected the spatial structure determined by the river plume. At the interface, there was a strong increase of taxonomic richness and diversity and of biomass at the edge of the under-ice plume, which reflected an ecotone situation. The significant positive relationship between species richness and algal biomass, at the ice-water interface, suggests that the interdisperslon of hab~ta ts , which characterizes ecotones, had a direct impact on the production of organic matter in the under-ice plume.