Should we expect strange attractors behind plankton dynamics – and if so, should we bother?

Chaotic behaviour can easily be generated from simple deterministic models of a number of ecological interactions. It is argued that these interactions, as well as the conditions necessary to produce chaos from them, are common in planktonic communities Furthermore, attention is drawn to the fact that sustained algal fluctuations are observed in micro-ecosystems that are kept under constant external conditions for as long as 10 years. These fluctuations are shown to have the same characteristics as those arising from a simple chaotically behaving model of competing algae. Recently, signs of chaos have also been shown in a series of plankton data from the field. It is concluded that there are, in fact, several independent reasons to believe that planktonic systems generally have a strange attractor, rather than a static or cyclic equilibrium. The chaotic nature has some implications that may warrant a reconsideration of our framework for thinking about plankton dynamics. For instance ' (I) the observed fluctuations can be seen as a special type of equilibrium, the nature of which can be understood from the relationships within the system; and (ii) although the range of possible behaviour of the system is well defined, the actual course of events is unpredictable, because small differences in initial condition expand in time exponentially. The conclusions from chaos theory sound quite spectacular, however, many of them do not appear to be essentially new to plankton ecology It is argued that the discrepancy between the mathematical findings and present-day knowledge of the mechanisms behind plankton dynamics are to a large extent semantic. Nonetheless, the seemingly small step of accepting that these systems are fundamentally chaotic implies the acceptance of the fact that we will never be able to predict their long-term behaviour accurately