Original paper

Long-term zooplankton body size and species changes in a subtropical lake: implications for lake management

Hambright, K. David

Abstract

Analysis of long-term (1970-2002) zooplankton body sizes in Lake Kinneret, as recorded in an historical zooplankton sample archive, combined with re-analysis of published long-term zooplankton taxonomic abundance data revealed previously undetected patterns in zooplankton biomass and demonstrates a profound long-term impact of planktivorous fish predation intensity driven by fishery harvest practices. During the 1970s, crustacean zooplankton biomass remained relatively constant at a mean (±SD) of 1.50 ± 0.26 g m−3, dropped precipitously in the 1980s reaching 0.57 g m−3 by 1993, and rebounded to 1.33 ± 0.19 g m−3 in the early 2000s. The 1980s decline reflects decreased cladoceran biomass due to a decline in mean body mass in the three dominant cladoceran genera (Diaphanosoma, Ceriodaphnia, Bosmina) and decreased copepod biomass that resulted from a shift in dominance by large Mesocyclops ogunnus to small Thermocyclops dybowskii. Although crustacean body sizes remained small through the early 2000s, cladoceran and copepod densities increased by ∼34 and > 300 %, respectively, after 1994 leading to a dramatic increase in crustacean zooplankton biomass. These patterns indicate an intensification in fish predation throughout the 1980s and 1990s, and although zooplankton biomass rebounded in 1996-2002 to ∼80 % of the 1970s levels due to sharp increases in crustacean densities, smaller cladoceran and copepod body sizes suggest that Lake Kinneret zooplankton continue to be strongly influenced by intense fish predation.

Keywords

historical sample archivezooplankton body sizeplanktivorylake kinneret