Testing the Remane Diagram: Occurrences of Benthic Macroinvertebrates in Oligohaline to Hyperhaline Salinities

Starting with the Remane diagram, various conceptual models have been proposed to show how species richness varies along a salinity gradient. However, as relatively few estuaries experience extreme hypersalinity, quantitative data are lacking to evaluate the model. We used data for 1891 samples of benthic macroinvertebrates from 12 estuaries in southwestern Australia (salinity 0–122 ppt) to determine the salinities in which 257 taxa were recorded. The pattern of richness differed from the conceptual models, with relatively few species (≤20%) recorded in freshwater and oligohaline salinities. Richness peaked at 35 ppt (seawater, 44%) before declining precipitously, with 21% and 10% of taxa recorded in hyperhaline salinities of 40 and 48 ppt, respectively. Taxa were recorded across the full salinity range, and several holohaline annelids, crustaceans, and insects were identified. Descriptive statistics and the frequency distribution of each taxon along the salinity gradient are provided. These identify stenohaline taxa and those with different extents of euryhalinity and how the occurrence of these taxa changes with salinity. The results help predict how benthic macroinvertebrate species and assemblages in estuaries in southwestern Australia and other Mediterranean climatic regions may shift due to climate change, particularly increased incidences and magnitude of hypersalinity.