Long-term changes of the chrysophyte population in Lake Tahoe

摘要

The analysis of long-term data collections provides great insight into the structure and function of ecosystems because it allows the identification of trends over background noise from inter-annual variation. This becomes particularly important for phytoplankton populations because they exhibit high seasonal and interannual variability and longterm datasets are useful to understand their response to environmental changes. In this study we used the long-term dataset of Lake Tahoe over a 25-year sampling period. The lake underwent several alterations over the last decades. The physical/ chemical changes include decreasing visibility (Swrvr et al. 2006), increasing primary production and shift from nitrogen to phosphorus limitation (GOLDMAN et al. 1993, JASSBY et al. 1999), and climate warming that has increased water column stability (COATS et al. 2006) resulting in stronger vertical thermal gradients and reduction in turbulent diffusion. Between 1982 and 2006 some phytoplankton groups have been able to adapt to the changing environment and maintain or increase their abundance (WINDER & HUNTER 2008). However, one group, the chrysophytes, significantly decreased over time. Chrysophytes are flagellated cells that are extremely good competitors for phosphorus in nutrient-poor environments (SANDGREN 1988) with low water temperatures and high transparency (REYNOLDS 2006). We analyzed the temporal and vertical dynamics of chrysophyte genera highlighted successful survival strategies and discussed possibilities for the chrysophyte decline.