The Dynamics of Mysis diluviana and Other Zooplankton in Three Oligotrophic Lakes

Mysids (Mysis diluviana) have been introduced to a number of temperate lakes to provide food to salmonids for recreational fishing. In many of these lakes, these mysids have changed the native zooplankton communities through predation. Mysids were introduced to Donner Lake, Fallen Leaf Lake, and Lake Tahoe in the mid-1960s and have changed the native zooplankton community of Lake Tahoe profoundly. We conducted mesocosm experiments to evaluate the effects of two native zooplankton taxa (Daphnia spp. and Epischura nevadensis) and juvenile and adult mysids on ecosystem function in Lake Tahoe and its more productive embayment, Emerald Bay. The results of these experiments indicate that these zooplankton play significantly different roles in the Emerald Bay ecosystem, but not in Lake Tahoe proper. This suggests that these zooplankton may play a larger role in shaping the ecosystem characteristics of the water column in Lake Tahoe if cultural eutrophication should eventually elevate Lake Tahoe’s trophic state to that of Emerald Bay’s. Additionally, we measured the environmental factors that influence mysid growth rates in Lake Tahoe. We found that adult growth rates significantly correlate with the depth of winter mixing, but juvenile growth rates significantly correlate with the mean summer. We also measured the pelagic reliance, trophic position, and carbon sources of mysids in Donner Lake, Fallen Leaf Lake, and Lake Tahoe and evaluated the role of wind-dispersed pollen in supporting mysid energetics. These analyses indicate that a variety of factors influence mysid production in these lakes, and the importance of the factors differs between the lakes