Metazoan zooplankton

Abstract

The Lake Kinneret metazoan zooplankton has been monitored since 1969 and currently includes the enumeration of 31 species of cyclopoids, cladocerans, and rotifers in samples collected fortnightly at five stations from around the lake. The zooplankton community has exhibited notable interannual and long-term variation since the start of the monitoring program that have included a decline in community size from the 1970s and 1980s to an extended period of low abundance and biomass in the 1990s followed by an increase during the first decade of the millennium. Along with the increase in abundances since the late 1990s, there has been an increase in interannual variation, which may be related to the unstable phytoplankton population and/or to the large changes in lake level. The introduction of an additional sampling protocol since 2003 has highlighted the highly vertically aggregated nature of some of the rotifer species often found in very high densities near the thermocline. Seasonally, the lowest densities are found during the summer and the highest during the winter–spring. There is no indication of vertical migration by zooplankton in the lake. The zooplankton are patchily distributed and repeated sampling indicates that abundance estimates collected over a period of a year could vary by a factor 2–3 just due to fine-scale patchiness. Zooplankton in the lake play an important role as key nutrient recyclers with microzooplankton accounting for > 85 % of the daily mineralization of P and N in the lake.