What effect did enclosing steelhead trout have on streambed algal densities?

Enclosing steelhead trout in streams typically leads to decreased algal densities and biomass. This phenomenon can be attributed to the feeding behavior of the trout. When trout are present in a stream, they consume not only the zooplankton and other aquatic organisms but also graze on algae. Their predation can reduce the overall algal biomass due to their foraging activities. Additionally, when fish are excluded, there may be a mismatch in the balance of nutrient cycling, further influencing the growth dynamics of algae.

Furthermore, the increase in algal density when trout are present can lead to a more competitive environment where certain algal species might dominate, resulting in decreased diversity among algal communities. By enclosing trout and studying the changes, it becomes clear that their presence directly impacts the algal community structure by reducing overall density and biomass. Thus, enclosing steelhead trout typically correlates with decreased algal densities and biomass.