Ecological Modelling, 27 (1985) 221-234 221 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands ANALYSIS OF STRUCTURAL STABILITY OF AQUATIC ECOSYSTEMS AS AN AID FOR ECOSYSTEM CONTROL FRIEDER RECKNAGEL University of Technology, Department of Water Science, Laboratory of Hydrobiology, Dresden (German Democratic Republic) (Accepted 8 October 1984) ABSTRACT Recknagel, F., 1985. Analysis of structural stability of aquatic ecosystems as an aid for ecosystem control. Ecol. Modelling, 27: 221-234. Structural stability of aquatic ecosystems is investigated by using the catastrophe theory. Subjects of investigation are management strategies for improving water quality which were determined by scenario analysis. Catastrophe theory is applied by simulating the isocline surfaces of the ecosystem's dominant behaviour variables. Simulations were performed with the help of the dynamic ecological model SALMO. The approach serves as a means of gaining information for a stable control of rational management strategies. INTRODUCTION Ecological systems are nonlinear dynamic systems which are extremely rich in their behaviour and tend to multiple stabilities. Multiple stabilities were observed, inter alia, for pest outbreaks in forest ecosystems (Ludwig et al., 1978), for changing species dominance in fishery systems (Jones and Walters, 1976) and in hypereutrophic ecosystems (Uhlmann, 1980). The investigation of this phenomenon is of great significance for ecosystem theory as well as ecosystem control (Fiering and Holling, 1974; May, 1977; Levin, 1979). There are two viewpoints from which to investigate multiple stability: microscopic and macroscopic. The microscopic consideration can be attri- buted to an internal optimization problem which is inherent in each ecosys- tem. As Casti (1979) has stated, the ecosystem is goal-oriented and "is attempting to minimize (locally) some cost function". One of the first investigations for gaining insights into the internal optimization of aquatic ecosystems was carried out by Radtke and Stra~kraba (1980). The macroscopic view is based on stability analysis, which may be 0304-3800/85/$03.30 © 1985 Elsevier Science Publishers B.V.