Detecting changes to the functioning of a lake ecosystem following a regime shift based on static food-web models

Ecosystem management requires a large base of knowledge regarding the main factors of the components in the system, the relationship between them and their relationships with the external forces that affect ecosystem behavior. In many cases, this knowledge is not always available. Therefore, analyzing previous events and determining the effects they had on the ecosystem can provide insights regarding the factors that caused the changes and their continuing effect on the ecosystem. This task is not simple, due to a large variability of factors in the ecosystem and the difficulty in identifying them. Based on the Ecopath approach, we developed a means for analyzing the Lake Kinneret ecosystem by comparing two mass balance models representing two very different periods. The first model is based on the period of 1990-1993, prior to a regime shift that occurred in the ecosystem and the second model is based on 2006-2010, a period characterized by unstable behavior in the ecosystem. Examining the differences between the two models allowed us to map changes in the ecosystem and to identify the changes and the ecosystem components affected by the regime shift. Using the results we demonstrate the potential of providing management recommendations regarding Lake Kinneret's ecosystem and fishery.