Background/Aims: Lateral connectivity in floodplain rivers is a major diver of high biomass and diversity in these ecosystems through increased energy inputs, and habitat extent. Increasingly this lateral connectivity is being lost due to increasing water resource development and expanding human landscapes, especially in the tropics. The fundamental principle of the flood pulse theory along with other recent iterations indicate that this seasonal inundation of terrestrial and adjacent wetland habitats provides the necessary energetic input and habitat expansion to sustain higher biomass and diversity of aquatic fauna than the main channel could sustain alone. Using stable isotopes and isotopic trophic niche metrics, the importance of this annual connectivity can be more clearly understood.
Methods: Stable isotopes, δ13C and δ15N of fin clips (n = 677 individuals, 27 species, 16 families) from fish communities were analysed to describe the isotopic trophic niche of river and wetland habitats on a floodplain river in tropical Australia. Four wetland sites and two river sites were surveyed over two wet seasons of connected and unconnected flood heights. Analysis conducted in R using SIBER package.
Results: We found that river fish communities, when kept isolated from adjacent wetlands and floodplain over failed wet seasons, have increased carbon range, trophic area, and trophic diversity, whereas wetland habitats appear to maintain similar niche space regardless of connectivity with the mainstem of the river. We found that when the river did connect with the wetlands through lateral connectivity in wet season flooding, the niches appear to overlap with wetland fish community isotopic trophic niches indicating consumption of abundant resources during connectivity. Providing a subsidy to the river as flooding recedes.
Conclusion: Using isotopic trophic niches to describe food webs in complex river floodplain ecosystems is useful in understanding how annual flooding supports high biomass and diversity in these environments. Maintaining lateral connectivity in these floodplain rivers is vital in providing the energy and habitat extent to maintain high biomass and diversity of the fish communities. Furthermore, understanding these connections in free-flowing rivers is vital in maintaining trophic ecology as water resources in these catchments are developed.