Hypersalinity: Global Distribution, Causes, and Present and Future Effects on the Biota of Estuaries and Lagoons

Estuaries, lagoons, and marine embayments that become hypersaline (salinity>40) are found around the world, but are most common in tropical, arid, and warm temperate climates with low and/or highly seasonal rainfall. The area of these systems range markedly from <0.1 to >10,000km², but are generally shallow (<2m deep) and located in microtidal regions (tidal range <2m). Hypersalinity is typically caused by a reduced or closed connection with the ocean, high evaporation, and/or low freshwater input. The characteristics of the biota present in hypersaline systems change markedly in response to increased salinity, with few species able to tolerate salinities >100, which can result in mass mortalities of flora and fauna and a simplification of the biotic community and food web. Climate change over the coming decades will potentially influence the extent of hypersalinity in estuaries and lagoons, by altering the frequency and magnitude of rainfall and the sea-level height. Changes in rainfall and sea level will also influence the extent of connectivity with the ocean.