Is Salinity Variability a Benthic Disturbance in Estuaries?
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Freshwater inflow is a driver of the functioning of estuaries, and average salinity is usually measured to identify the effects of inflow in salinity-zone habitats. However, salinity variability could act as a disturbance by producing unstable habitats, leading to the question: is salinity variance an indicator of benthic disturbance, and therefore a driver of community stability? The macrofauna communities of five estuaries that lie in a climatic gradient on the Texas coastline were analyzed using a 26-year data set. Comparisons within and between estuaries with different inflow regimes were used as a natural experiment to simulate press disturbance events (i.e., climatic inflow) and pulse disturbance (i.e., floods) in maintaining community stability. Salinity average and variance was compared with benthic community diversity, evenness, and species richness. Salinity variance was more correlated to benthic diversity for each estuarine system (r = −0.6610; p = 0.0015) than average salinity (r = 0.3818; p = 0.0967). As salinity variance decreased (i.e., stability increased), diversity levels of benthic communities increased, and areas with mgore freshwater inflow displayed lower levels of benthic diversity. These findings advance a component of the general theory of diversity maintenance that persistent stressors, such as salinity variability, can influence diversity.
KeywordsPress and pulse disturbances Infauna Freshwater inflow Long-term data Diversity-stability
The data collection has been funded by many agencies (with grants to PM) over many years. The Texas Water Development Board (TWDB) provided the initial funding that started the project in 1987 and continues to fund this work in 2015. Additional funding has come from the US Environmental Protection Agency (Gulf of Mexico Grant MX954526), The National Oceanic and Atmospheric Administration (CAMEO Grant NA09NMF4720179), and the Harte Research Institute for Gulf of Mexico Studies (HRI). This research would not be possible without the diligent and consistent sampling and identification of benthic organisms led by Rick Kalke (HRI) and Larry Hyde (HRI). A final thanks to Terry Palmer (HRI) for helping with the statistical analysis in SAS and for generating the map of the study area.
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