Old Faithful Virtual Visitor Center

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Hydrothermal Influx


More types and greater numbers of insect larvae are present in the parts of the Firehole River warmed by hydrothermal influx. The bicarbonates increase plant growth, which means there are more surfaces for bottom-dwelling creatures to attach themselves, as well as more available food.

Large swaths of plants sway in the current of the Firehole River

This tiny macroinverterbrate looks similar to a shrimp
A small caddis fly clings to a branch

The macroinvertebrates in the thermally influenced waters vary more in shape and size than their counterparts in cooler water, and some species demonstrate changes in respiration, growth rates, and feeding behavior.

Most stream insects have an annual turnover-once a species hatches, the entire population disappears from the water and doesn't reappear until the following year. However, in thermally influenced areas, some of these stream insects are reproducing two times a year!

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This work is supported by

National Science Foundation    Yellowstone Park Foundation
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