Climate Change Facilitates the Formation of Natural Barriers in Low-Inflow Estuaries, Altering Environmental Conditions and Faunal Assemblages

Climate change in Mediterranean regions is projected to cause declines in rainfall and higher temperatures and evaporation, which will enhance the formation of barriers at the mouth of low-inflow estuaries and potentially also in the riverine reaches. This review uses data from estuaries in south-western Australia across a rainfall gradient to describe how these barriers form and the effects they have on environmental conditions and biotic communities. The formation of barriers disconnects the estuary from adjacent freshwater and marine environments, prohibiting the movements of fauna and lowering taxonomic and functional diversity. Moreover, the longer periods of bar closure can result in increased frequency and magnitude of hypersalinity, hypoxia and nutrient enrichment. These conditions, in turn, act as stressors, often synergistically, on the floral and faunal communities. In some cases, mass mortality events occur, and some estuaries dry completely. To ensure the functioning of such systems in the future, regular monitoring across a wide range of estuaries is needed to understand how climate change is impacting different types of estuaries. A range of management options are discussed that may help mitigate the effects of increased barrier formation but should be employed as part of a whole-of-catchment approach and regularly evaluated.