Glacial stream ecosystems and epilithic algal communities under a warming climate

Climate change is accelerating the global loss of glaciers with potentially striking consequences for downstream ecosystems. However, there exists limited evidence of the ecological impacts of glacier loss in meltwater streams, particularly in those outside of North America and Europe. We provide a review of the abiotic conditions in glacial streams that are potential factors of their ecosystem function and biodiversity with an emphasis on their key primary producers, namely rock-attached algae or “epilithon.” Here, shrinking glaciers discharge over time less turbid melt waters, resulting in slower moving and more transparent stream conditions that are also warmer and more chemically dilute. We hypothesize that these environmental changes will stimulate epilithic algal growth while also shifting its community structure towards larger and less nutritious taxa. Although such an increase in algal growth may benefit the productive harvestable fish capacity of certain mountain streams, a potential negative trade-off involves the proliferation of nuisance algae (e.g., Didymosphenia geminata), which thrives under clear, nutrient-poor mountain conditions. We advocate the use of long-term ecological monitoring programs and experiments coordinated across global mountain ranges to better predict and understand the ecological consequences of loss of glaciers on mountain stream ecosystems.