By Carson Jeffres and Jeffrey Mount
When ecologists talk about improving habitat for native fishes, they often focus on enhancing food webs and their productivity. Food webs (what we used to call food chains) are inherently complicated and are often discussed in the abstract. They start with primary producers (e.g. plants and phytoplankton) that feed primary consumers (invertebrates), which ultimately feed fish, such as juvenile salmon—a common target of restoration efforts.
In this video we get the rare opportunity to observe food web productivity in action. On Big Springs Creek, a tributary to the Shasta River, geologically derived nutrients fuel an unusually productive food web. These nutrients are incorporated in groundwater as it passes through the volcanic rocks of Mount Shasta and marine sedimentary rocks that underlie the mountain.
As the groundwater emerges as springs, nutrients create rapid and abundant aquatic plant growth. These plants, in turn, support exceptionally high numbers of aquatic invertebrates. In this way, nutrient rich groundwaters are churning out voluminous, high-quality fish food.
Freshwater shrimp, or scuds, in Big Springs Creek. Video by Carson Jeffres
Invertebrates drift downstream in the water column, they are eaten by juvenile coho salmon. Because the spring water temperature is constant, it provides high quality growing conditions throughout the year for all components of the food web. These ideal growing conditions (constant temperature, unlimited food resources and high quality habitat) allow the juvenile coho to grow much faster than in adjacent watersheds where these conditions are not present. These coho are roughly twice the size of similarly aged fish only 40 miles away.
Sit back, take a minute and enjoy a food web in action on Big Springs Creek in Northern California.
Carson Jeffres is a fish ecologist at the UC Davis Center for Watershed Sciences. Jeffrey Mount, a geology professor, is the Center’s founding director.