The effects of early and late ice off on zooplankton community structure in subalpine Castle Lake, California

ERIN SUENAGA; JOSHUA CULPEPPER; SUDEEP CHANDRA; FACUNDO SCORDO

Virtual

Congreso; ASLO-SFS 2020; 2020

The Association for the Sciences of Limnology and Oceanography.

Shorter ice duration and warmer waters are being observed in temperate lake ecosystems as winter conditions become more variable with a changing climate. The duration of ice cover impacts the physical and chemical conditions of a lake and, in turn, influences the ecological processes occurring in the following seasons. Here, we compare the succession of zooplankton community composition and biomass, and primary productivity (PPr) throughout the growing season in the subalpine Castle Lake (z=30m), California, after early and late ice off years between 1983 and 2015. The mean ice off day at Castle Lake during the study period was on Julian day 129, with earliest ice off dates recorded on Julian days 51 and 57 (2015 and 2014, respectively) and the latest ice off date recorded on Julian day 187 in 1983. We found evidence of compositional and successional differences in the zooplankton communities in the early summer months between late and early ice off years, with higher occurrences of cladocerans and cyclopoids and higher total biomass with earlier ice off. We also observed lower rates of PPr in the epilimnion in years with a longer ice cover period at the beginning of the growing season, and generally lower rates of PPr throughout the growing season with later ice off. This study underscores the importance of winter lake conditions in influencing productivity and ecosystem functioning during the growing season, and encourages more research looking into the impacts of changing snowpack and shorter ice cover on freshwater systems.