Editorial: Animal Mass Mortalities in Aquatic Ecosystems: How Common and Influential?

From the introduction: The prototypical animal mass mortality in aquatic ecosystems is the annual spawning migration of Pacific salmon (Oncorhynchus spp.) that can transport thousands of kilograms of labile organic resources to rivers and lakes. However, many other mass die-offs of vertebrates and invertebrates can strongly influence the structure and function of aquatic ecosystems. Here we discuss the spatial and temporal occurrence of mass mortality events in aquatic and riparian systems, as informed by the preceding series of papers in this special issue, and their influence on ecological processes. Fish in the families Salmonidae and Clupeidae undertake annual mass migrations that often result in their death in the ecosystem where they spawn, and therefore their macronutrients (C, N, P) and even micronutrients subsidize recipient ecosystems. In contrast, stressful conditions such as oxygen depletion or toxic algal blooms can result in unpredictable fish and mussel die-offs. Terrestrial animals ranging from insects to wildebeest also subsidize aquatic and riparian ecosystems during mass mortality episodes associated with migrations or adult emergence from or near water bodies. We propose a paradigm of programmed vs. catastrophic death whereby recipient ecosystems vary along a gradient in their history and capacity to process these subsidies based on the predictability and timing of the resource pulse. Such mortality events may be increasing in frequency and severity with global environmental change, and therefore a more robust understanding of their ecological effects is needed to inform theory and application.