Effect of a total solar eclipse on the surface crowding of zooplankton in a freshwater lake ecosystem

Zooplankton surface crowding in a freshwater lake ecosystem during a total solar eclipse (maximum eclipse at 06:28:43 Indian Standard Time, 22 July 2009) was studied in relation to ambient physicochemical conditions and compared with the crowding that occurred during pre- and post-eclipse days. Rapid light attenuation on the eclipse day led to changes in zooplankton surface crowding, which manifested as alterations to community structure and statistical parameters. Zooplankton diversity and density varied depending on the day (either the pre-eclipse day, the eclipse day, or the post-eclipse day) and the sampling time considered. A total of 20 zooplankton species were recorded during the study. On the day of the eclipse, the highest zooplankton density in the surface water was recorded just after the end of totality at 06:30 IST. The populations of two adult cladoceran species (Alona rectangula rectangula and Chydorus sphaericus) were particularly prominent in the zooplankton, whereas rotifers were almost absent from the surface water during the eclipse. Rather than decreasing, the primary production of the phytoplankton increased on the day of the TSE compared to that seen on the control days. Comparatively high Lindeman’s efficiency values were observed during the eclipse, indicating particularly efficient utilization of photons in photosynthesis.