Penguins at the freshwater-marine boundary:Overlooked ecological linkages and climate-change risksOA

Penguins are usually framed as marine predators,yet freshwater can strongly alter the environments in which they forage,breed and survive.This narrative mini review synthesises evidence for how river outflows,glacial meltwater,snowmelt and rainfall shape penguin ecology across estuarine,fjord,colony and climatic settings.In southern Australia,river plumes reorganise penguin foraging habitat,and prolonged drought linked to reduced coastal freshwater delivery has coincided with major demographic decline.In Antarctic and subantarctic fjords,glacial meltwater can enhance stratification,alter prey depth and influence penguin foraging conditions,but its effects are not uniformly beneficial because increased turbidity,contaminant transport and physical disturbance may also degrade habitat.At breeding colonies,snow can provide a local freshwater source that helps reduce osmoregulatory costs,whereas excessive meltwater and rainfall can flood nests,collapse burrows,chill chicks and reduce breeding success.Physiological and isotopic evidence further suggests that freshwater influences penguins not only through habitat and reproduction,but also through hydration,salt balance and longer-term environmental archives.Across systems,freshwater acts both as a resource and a hazard,and its effects depend on timing,magnitude and local context.This freshwater-centred perspective highlights penguins as indicators of linked land–sea and ice–sea change,clarifies key thresholds and uncertainties,and points to more targeted priorities for future interdisciplinary research.