Flow regimes among rivers influences benthic biota biodiversity, but not abundance or biomass, in intertidal mudflats and sandflats in wet-dry tropical estuaries

Flow is a fundamental driver of ecological processes in river networks and estuaries. In estuaries, river flow interacts with tidal and wave energy to structure the physiochemical environment and the relative strength of these interactions changes in space and time. Thus, ecological processes in estuaries are best understood within the context of these physical processes. In this study, we explore how changes in river flow regime influence the structure of benthic communities in three estuaries in northern Australia's Gulf of Carpentaria. This region resides in the wet-dry tropics and the rivers have among the most variable flow regimes in the world. During two sequential dry seasons, we compared measures of benthic macroinvertebrate biodiversity, abundance, and biomass in intertidal mudflats and sandflats among three estuaries with differing river flow regimes. We found that the number of consecutive days of zero river flow during the preceding dry season best explained inter- and intra-annual patterns in benthic community composition. Specifically, we suggest that the dry season river flow regime dictated the salinity regime of each estuary, which in-turn influenced benthic community composition. However, neither the differences in the salinity regime or community composition influenced total abundance or biomass of the benthic community, indicating that the regional taxa pool currently contains enough functional redundancy to maintain abundances and biomasses under various physicochemical conditions. This in turn provides consistent resources for higher trophic levels such as birds and fish.

Automated summary

Flow is a fundamental driver of ecological processes in river networks and estuaries. In this study, the researchers explored how changes in river flow regime influenced the structure of benthic communities in three estuaries in northern Australia's Gulf of Carpentaria. They found that the number of consecutive days of zero river flow during the preceding dry season best explained inter- and intra-annual patterns in benthic community composition. The study also revealed that the regional taxa pool currently contains enough functional redundancy to maintain abundances and biomasses under various physicochemical conditions.