No Project associated with this Finding

Primary goals of this study are to examine the role crayfish play in determining the periphyton
and biofilm dynamics in Lake Tahoe while understanding the nutrient limitation of periphyton
which has not been examined prior to this study. In addition, we describe the contemporary
periphyton biomass through the nearshore littoral zone to demonstrate the concern for the
nearshore should not just be focused on the upper littoral waters at the edge of the lake. The
Nearshore of Lake Tahoe includes the area of the lake with a depth shallower than 30 feet, or to a
minimum width of 350 feet from the shoreline.

In this study, we find that periphyton growth in Lake Tahoe is limited by nitrogen throughout
the photic zone. This contrasts to the pelagic (open water) phytoplankton community which is
co-limited by nitrogen and phosphorus or sometimes just nitrogen. This suggests that if we are
going to model, manage and understand the dynamics of bottom algal production in the lake’s
nearshore we need to consider sources and loads of nitrogen (e.g. groundwater, run off, internal)
supplied to periphyton. One important “internal” and localized contribution of nitrogen may
come from the crayfish. We an experiment we suggest, a large bioavailable concentration of
dissolved nitrogen can come from crayfish excretion with greater concentrations from larger
crayfish. Thus, as crayfish seasonally migrate along the lake surface, as demonstrated in this
study and elsewhere, crayfish produce local available nitrogen at the rock-sediment-water
interface which should stimulate periphyton growth which is already limited by nitrogen. Other
research shows that available nitrogen from biological organisms can play an important role in
addition to the growth of algae particularly during periods where the supply of nutrients is in
shorter supply. Simply, organisms can matter in providing feedbacks to algal and bacterial
growth.