Alternate Stable States – Sea of Galilee (Lake Kinneret), Israel

Collaborators - Tamar Zohary and K. David Hambright

System hysteresis and selection of alternate stable community states: A case study using the 34-year plankton record from Lake Kinneret (Sea of Galilee), Israel

The notions that alternate stable-states occur in ecosystems and that selection of alternate states is stochastic, have recently been challenged. Through analyses of a 34-year record of phytoplankton, zooplankton, and physicochemical parameters from Lake Kinneret, Israel, we show that alternate stable-states occurred in this system. The hysteresis alternate stable-states model provided an excellent framework for understanding the complexity of the system’s dynamics. The alternate states were characterized by the presence and absence of spring blooms of the dinoflagellate, Peridinium gatunense, and the underlying phytoplankton community structure. The two states were defined by distinctive assemblages that persisted for most of the year. Grazing pressure exerted by commercial fish on plankton appeared to be the “less dynamic” variable in the context of the hysteresis model, and expression of the two alternate states in Lake Kinneret was only possible after this variable crossed a threshold when the fishery collapsed. When expression of alternate states occurred, the structure of the zooplankton community appeared to be the “more dynamic” variable that controlled which state was expressed. Because characterizations of the zooplankton community that defined is distinctness in these alternate states were complex, i.e., involving 35 categories defined by species and life stage, abundance of dominants and non-dominants played a role, and the ratios between the categories were important, the factors that govern which alternate stable-state is expressed in Lake Kinneret might indeed be stochastic.