Abstract:
Selected zooplankton from three oligotrophic lakes in Oregon were studied to determine whether or not their instantaneous birth rates and densities could be used in lake classification. The species of zooplankton studied in their respective lakes were Daphnia, pulex in Crater Lake, Daphnia longispina in Odell Lake, and Daphnia longispina and Diaphanosoma brachyurum in Woahink Lake. Instantaneous birth rates, densities and other population parameters were estimated for
these species. The species studied in Odell and Woahink Lakes were also collected to determine the relationship between diel vertical distribution of these species and the temperature and phytoplankton primary production occurring in the lakes, Woahink Lake Daphnia had the highest instantaneous birth rates for Daphnia sp. of the three lakes. However, Woahink Lake Daphnia
carried fewer eggs and were less dense than Daphnia in Odell Lake on every sampling date. Crater Lake Daphnia were usually less dense and had lower instantaneous birth rates than was observed for the Woahink Lake Daphnia. Because of changes in the density of zooplankters from one year
to the next, as occurred with Daphnia in Crater Lake, and the lack of correlation between phytoplankton primary production and density, as occurred for Daphnia and Diaphanosoma in Woahink Lake, application of these population dynamics to lake systematics were nullified. The finite birth rate also lacked the expected correlation with phytoplankton primary production for all the selected species in the study lakes. The lack of correlation may be due to interactions between the total species of zooplankton present in the lakes. If instantaneous birth rate and density were calculated for all the species in each lake it might be possible to use them for lake classification. However, the time expended in analysis would be prohibitive. The did vertical distribution of Daphnia in Odell. Lake showed a typical migration to the surface at night and a return to deeper water during daylight hours. In Woahink Lake, however, Daphnia and Diaphanosoma were found to migrate only when the lake reached temperatures near 15°C or greater. The phytoplankton primary production occurring during the periods when migration did not take place, was equal to or greater than that occurring during some of the periods when vertical migration did occur. These observations may or may not have significance since the density of these two species did not show correlation with primary production.
