Chapter 25 - Benthic Algae and Cyanobacteria of the Littoral Zone

Abstract

Benthic algae and Cyanobacteria grow on illuminated, submerged substrata such as rocks, sediments, plants, and animals in lake and river littoral zones. Diatoms, green algae, and Cyanobacteria dominate benthic algal assemblages and cover submerged surfaces with layered biofilms or more structurally complex, upright turfs. Light and nutrients are essential for benthic algal growth, and the water column, groundwater, sediments, and living hosts (both plants and animals) are nutrient sources. Light availability strongly influences periphyton production seasonally and across depth gradients. Wave disturbance and grazing strongly limit the accumulation of benthic algal biomass. Diatoms are favored by grazers but are able to persist in the face of heavy grazing. In the absence of grazing filamentous green algae often gain ascendancy. Benthic algae exchange metabolites with and compete with heterotrophic microbes in periphyton. Benthic algae compete with macrophytes and phytoplankton for light and nutrients and can dominate whole-lake primary production (autotrophic structure), especially in small, clear lakes. Eutrophication diminishes benthic contributions to autotrophic structure. A wide size range of animals consume benthic algae, and periphyton contribute to the growth of the majority of fish and invertebrate diversity in lakes. Thus benthic algal contributions to lake food webs are usually greater than would be predicted based on their contributions to whole-lake primary production. Climate warming and increased mobilization of nutrients will tend to increase the growth and biomass accumulation of benthic algae. In subarctic and boreal regions increased loading of dissolved organic carbon (DOC) associated with altered rainfall and snowmelt will tend to reduce the role of epipelic algae in lake ecosystem function. Benthic filamentous algal blooms (FABs) are increasingly common in clear lakes worldwide.