The influence of temperature on periphyton was studied in experimental streams over a range of temperature from 13.5 to 38 °C. Response of periphytic algae was measured as changes in biomass, diversity, biovolume, and growth rate during a seven-day colonization period. Maximum biomass developed at 27 °C during early stages of colonization and optimum temperature associated with maximum biomass shifted later to 33 °C. Species richness decreased rapidly as temperature increased from 13.5 to 33 °C. The community shifted as temperature increased from evenly co-dominating low-temperature diatom taxa to a few dominant intermediate-temperature diatom taxa, and finally to a few taxa of cyanobacteria. Considerable differences among species growth rates were observed across the temperature gradient. Low-temperature diatoms had high growth rates within a low temperature range and intermediate-temperature diatoms maintained a relatively constant growth rate from low to intermediate temperatures but failed to grow at high temperatures. Cyanobacteria grew poorly or not at all at low temperatures and grew most rapidly at high temperatures. These results demonstrate the importance of the direct effects of climate change forcing by temperature on periphytic community composition in streams and suggest that warmer climates will increase cyanobacterial abundance and reduce diatoms in stream periphyton, which may lead to changes in food webs and degradation of ecosystems.
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