In the Eel River, CA, Cladophora glomerata forms the base of the food web. Cladophora hosts a rich epiphytic assemblage that includes, autotrophs dominated by diatoms, and heterotrophs that include decomposers (watermolds, fungi), parasites and predators (e.g. Amoebozoa, ciliates). The epiphyte assemblage changes from early spring to late fall. This research is important to understand the foundation of food web structure and energy flow in streams. We manipulated temperature using streamside flow-through chambers and tested how temperature affects epiphytes at four successional stages of Cladophora. We sequenced the 18s amplicon gene with primers that are universal to all eukaryotes.
Temperature and algal stage played key roles in shaping the epiphyte assemblage. Autotrophs dominated all treatments. Under ambient temperatures, the relative abundance of autotrophs ranged from 85% to 96%. The relative abundance of autotrophs decreased with warming and ranged from 55% - 90%. Watermolds and fungi which are the primary decomposers, drove the overall increase in heterotrophs. The increase in decomposers reflects an increase in decomposition within the algal mat with warming. With succession, Epithemia spp, became the dominant autotroph. Epithemia is a diatom with cyanobacterial endosymbionts, which fix nitrogen. Epithemia decreased with temperature suggesting a decrease in n-fixation with warming.
In conclusion, temperature and algal succession play a crucial role in structuring microbial communities. This contributes to understanding complex ecological interactions in freshwater systems and has implications for predicting ecosystem responses and microbial impacts on element cycling.