Lake benthic algae: toward an understanding of their ecology

Lake phytoplankton studies outnumber studies on lake periphyton by an order of magnitude, and most periphyton research has been done in streams. Most benthic algal taxa found in lakes also can be found in lotic systems, but assemblages and taxa differ in a number of ways. The ecological characteristics of some lake benthic algae reflect habitat coupling. Littoral zones (benthic areas above the light compensation depth) are areas of high productivity and biodiversity. The proportion of benthic and planktonic primary production (autotrophic structure) is a key ecosystem property. The distribution of lake benthic algae is markedly influenced by the depth gradient and substratum, and assemblages change with depth from epilithic and epiphytic rheobionts to epipsammic and epipelic limnobionts. At shallow depths, periphyton must cope with the effects of high radiation, water-level fluctuations, wave action (e.g., desiccation, ultraviolet radiation exposure, shear stress), and seasonal shifts in temperature. This situation selects for widely distributed rheophilic species. In contrast, the deeper littoral zone is stable and hosts a distinct subset of lentic periphyton. However, species experience low light intensity, which becomes increasingly severe with increasing depth, and are often threatened by eutrophication-driven increased shading by phytoplankton. Besides change across depths and substrata, adaptations to disturbance levels, competition, microdistribution of phenological stages, and physiomorphological regulation generate multiple and complex spatial patterns at different scales. Lake shores are the focus of human activities with significant consequences for periphyton. In this review, we introduce a series of 15 papers on the topic and suggest directions for future research. Overall, this special series illustrates that, despite the many important ecosystem services provided by lake benthic algae, the topic is understudied.