Periphyton and Benthic Invertebrate Production in Relation to a Fluctuating Water Regime with Comments on Fish Habitat and Diet

A study was conducted in the lower Nelson River in northern Manitoba in 2006/2007 to provide an understanding of lower trophic productivity influenced by fluctuating water levels and its contribution to productivity of Longnose Sucker.  Rock baskets were deployed to sample periphyton and benthic invertebrates. In both years periphyton production was higher in permanently wetted habitats in July but higher in intermittently exposed habitats in August and September. Seasonally, mean ash free dry weight for all habitat categories pooled was lowest in July, followed by August and September in both years. The mean density of benthic invertebrates was highest in permanently wetted habitats, followed by the intermittently exposed habitats. Taxonomic richness at the family level was greatest in permanently wetted habitat compared with intermittently exposed habitat in July and August. However, in September, taxonomic richness was greatest in intermittently exposed habitat. In both July and August, stomach contents of Longnose Sucker were dominated by algae in comparison to invertebrates. Although, invertebrates were a smaller proportion of the diet, those found coincided with the abundant taxa found in rock baskets.