Beyond the trends: The need to understand multiannual dynamics in aquatic ecosystems

Interannual variability is a pervasive feature of aquatic ecosystems. This variability results from shortand long-term dynamics of biotic and abiotic origin, inclusive of multiannual variability and long-term trends. Although understanding short-term variability and forecasting directional change are important research efforts, far less attention has been paid to oscillatory, or wave-like dynamics that play out over multiple years, in aquatic ecosystems. In this essay, we argue that understanding these modes of variability—in addition to directional trends and intraannual patterns—and their underlying causes are necessary for understanding aquatic ecosystem functioning over long time periods for effective conservation and management. Fortunately, given the growing availability of multidecadal data, development of statistical tools, and the urgent need to forecast change, the field can readily adopt multiannual dynamic thinking into our understanding of aquatic ecosystems.