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 5 0 % ] could b e 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 s p a t ~a l processes. In 1990 (strong inshore-offshore g r a d ~e n 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~tats, which characterizes ecotones, had a direct impact on the production of organic matter in the under-ice plume.