Community Dynamics of the Benthic Algae in Cobble Based Streams in South-East Quensland

Abstract

Benthic algae are largely present within a polysaccharide matrix called ‘biofilm’ where they coexist as a community with heterotrophs such as bacteria, fungi and other organic matter that attaches to substrates. In upland stream ecosystems, benthic algae serve as a basal food source in riverine food webs and immobilise nutrients from the water column via the processes of assimilation and remineralisation. From a conservation biodiversity perspective, upland benthic algal assemblages are not only a biodiversity hot spot for rare, endangered and endemic freshwater species but also a source of propagules for downstream reaches. Diatoms (Division Bacillariophyta) are the most abundant and diverse taxonomic group commonly dominating the benthic algal communities in upland streams, and are major contributors to primary productivity providing a particularly high quality food source compared to other benthic algal taxa and terrestrial matter. The quantity and quality of benthic diatoms as food sources for consumers in streams change spatially and temporally can cause resource shortages and dietary shifts in consumers which, in turn, track these changes to the upper food webs consumers and the benthic food web patterns. Despite their ecological importance and previous study by taxonomists and ecologists world-wide, patterns of benthic diatom taxonomic composition and their underlying factors are largely unexplored in Australian subtropical upland river ecosystems. Therefore, identification of the biodiversity, distribution and abundance of diatom taxa that sustain river food webs, is of fundamental importance in understanding how rivers function as ecosystems.