Improved understanding of the influence of stream flow on food webs will complement our understanding of the influence of flow on habitat and connectivity and this knowledge will enable better management of environmental flows within the Murray-Darling Basin. The EWKR food web theme reviewed existing conceptual models and empirical research during its conceptualisation phase in order to assess our current knowledge status and the knowledge gaps surrounding the influence of flow on lowland river food webs.
Empirical research carried out within the EWKR food web theme set out to address knowledge gaps identified within the conceptualisation phase. This work was undertaken at three scales: 1) mesocosm 2) river and 3) basin. Mesocosm experiments showed that green algae are a key basal resource for consumers, providing a high-quality food source. Essential fatty acids were traced from green algae through Food Webs from invertebrates to fish. Dissolved organic carbon (DOC) based Food Webs by contrast, provided the lowest invertebrate density, richness and lowest fish growth and survival.
Patterns observed in mesocosms were reinforced by observations made at the river scale. Although floodplain inundation is known to be important for riverine productivity, field experiments suggest that reconnection of floodplain habitats to the main channel following initial inundation may be an important management application. Wetland and anabranch habitats contained higher concentrations of essential fatty acids in the water column than river habitats. Differences in food quality between habitats were attributed to a higher concentration of green algae in the water column within floodplain habitats. River scale research also showed that consideration of specific waterbird species trophic requirements is important when tailoring management of environmental watering to maximise food availability to support waterbird recruitment.
Basin scale research conducted by the food web theme has led to the development of a monitoring tool for managers that evaluates changes in the trophic position of fish communities in the Murray-Darling Basin. The trophic niche indicator provides a cost-effective annual monitoring tool that can assess the influence of environmental flows on food sources of native fishes.
Foundational, mesocosm, river and basin scale activities informed development of a model of energy pathways from water provision through to larval fish that builds on our current understanding of trophic responses to environmental watering. Our work shows that by targeting shifts in diet composition and producer quality, watering events can be designed to disproportionately benefit fish.