Flows and fish community tropic ecology in tropical riverfloodplains

The natural flow regime of rivers moves energy longitudinally from upstream to downstream, and laterally under flood conditions to floodplains. Flooding connects river channels to floodplains which support a high biomass and diversity of plants and animals. Floods inundate terrestrial habitats in most years in the tropics, and this has allowed fish communities to develop trophic and life-history adaptations allowing them to use food resources produced by flood pulses. In comparison with other flow variables such as no flow days, falling hydrograph and low-flow conditions, flood pulses are considered to be an important but understudied component of the natural flow regime. In tropical savannah river-floodplains, the flood pulse provides an important food surplus that supports a high diversity and biomass of animals beyond what the main channel could otherwise support. This surplus may also be supporting fish condition and biomass through the dry season when resources become limited and biotic factors increase further limiting access to quality and abundant energy sources.
Understanding the drivers of trophic diversity and biomass in tropical savannah river-floodplain ecosystems is important because anthropogenic impacts, such as water resource development and floodplain land-use modification, are increasing in the tropics. The flow regime of large free-flowing rivers and their smaller tributaries are increasingly being modified due to water extraction for increasing agricultural needs resulting in the alteration of the natural flow regime. Changes to the natural flow regime are likely to disrupt fish community trophic diversity and biomass production with ecological and socio-economic consequences for recreational, commercial and indigenous fisheries and values.
In this project I hope to improve our understanding of the importance of flow regimes to fish community species richness and trophic diversity in tropical river basins of Northern Australia. Field studies will focus on floodplain habitats of the free-flowing Roper River and examine seasonal variation in fish condition and food quality over the wet season on the terminal floodplain wetlands using Stable Isotope and Fatty Acid analyses. I will explore changes across trophic guilds over consecutive wet seasons and explore how each guild is impacted by seasonal flooding. I will also investigate how condition and food quality changes over the dry season in permanent floodplain wetlands of varying water quality. I hope this research adds to the understanding of links between tropical Australian river food webs and annual river flow discharge variability, which may inform water resource development and policy while preserving aquatic ecosystem diversity and resilience.