A STRATEGIC SIMULATION-MODEL OF A FJORD ECOSYSTEM

We formulate a strategic simulation model of a fjordic ecosystem, payi ng careful attention to consistency of spatial and temporal scales. Ou r model incorporates all the major physical and biological elements of the system but is simple enough to allow unambiguous identification o f the mechanisms underlying its behavior. Despite this simplicity the model is capable of semiquantitative agreement with the observed behav ior of the Killary Harbor ecosystem over the 1981 season. The key conc lusion from our analysis of the model is that because of the very high rates of tidal and freshwater flushing in Scottish sea-lochs, the per sistence of such systems is ultimately determined by the balance of nu trient import and export in a manner analogous to a laboratory chemost at. Except at the peak of the spring bloom, inorganic nitrogen supply exceeds biological demand, so that primary production is controlled by physical factors (temperature and irradiance) and the activities of h igher trophic levels. The size of the spring phytoplankton bloom is ma inly determined by the dynamics of the following zooplankton bloom and is thus strongly influenced by the over-wintering success of zooplank ton inside the system as well as zooplankton immigration from the sea.