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Polyunsaturated fatty acids (PUFA) are essential components of cell membranes and reproductive and sensory organs in vertebrates and are largely acquired through their diets. Accordingly, identification of the dietary sources of PUFA is an important consideration in food web studies.We collected fish, macroinvertebrates (aquatic and terrestrial), and plants (aquatic and terrestrial) from floodplain and river channel habitats in a tropical river catchment in northern Australia, to identify food sources and habitats that provided lipid and PUFA rich food that sustain fish populations.The composition of most FA in fish was similar to that reported from other freshwater tropical environments, with the exception of their higher arachidonic acid content. Fish were found to derive their fatty acids primarily from aquatic sources of food and had similar FA composition to aquatic macroinvertebrates. Aquatic macroinvertebrates fed on aquatic plants (algae) and had higher total lipids and FA contents than plants and fish, providing a more concentrated source of PUFA for fish. Fish obtained most of their FA from their diet except for docosahexaenoic acid (DHA), which they must synthesize due to low DHA in algae and macroinvertebrates.There was no overall difference in basal dietary FA composition between floodplain and river channel habitats. However, macroinvertebrate taxa varied in their lipid and PUFA content.Food quality for fish may therefore vary between habitats as a consequence of differences in macroinvertebrate community composition. Given the high algal production on floodplains compared to the river channels, these habitats are likely to represent the major source of high quality food for fish and other aquatic consumers, and conserving habitats that are rich in lipids and PUFA is important for maintaining healthy fish communities. [ABSTRACT FROM AUTHOR]

Floodplain wetlands provide an important subsidy for riverine food webs as sites of high algal production. However, this subsidy depends on the degree of landscape connectivity during flood pulses, which provides the opportunity for movement of higher order consumers between rivers and floodplains to access these productive habitats. Changes in floodplain inundation extent and duration, due to variable wet season flows or water resource development (WRD), can impact landscape connectivity and ultimately the magnitude of the food web subsidy.We explored landscape connectivity using graph theory and derived four new metrics to measure how different flow scenarios can affect connectivity and algal production. We considered a historic scenario with the present level of water resource development in our study area, the Mitchell River, and a WRD scenario with the inclusion of three new dams in the catchment. We generated 240 unique daily spatial graphs, using surface water inundation maps across 40‐day flood events to compare a dry year (2006), an average flow year (2001) and a wet year (2009) with and without a WRD scenario.Drier years and WRD scenario resulted in floodplain fragmentation, potentially constraining the movement of higher order consumers. Changes in connectivity due to WRD resulted in predicted reductions of up to 26% of algal production on the floodplain that was otherwise connected to the main river channels.Synthesis and applications. The approach developed in this study provides new metrics to identify how changes in floodplain surface water extent due to water resource development and climatic variation may impact ecosystem function such as connectivity that facilitates access of higher order consumers to primary production in floodplain wetlands. With a direct link to river flow alteration, these metrics can inform catchment planning and management to ensure that the conservation of floodplain ecosystem functions is adequately considered in water resource management decisions. [ABSTRACT FROM AUTHOR]

Rice-shrimp culture systems occur throughout Asia where there are seasonal alterations of fresh and saltwater availability. During the dry season, black tiger shrimp are grown at low densities, and in the wet season, rice, or rice and shrimp are grown together. Previous studies point to issues with suboptimal rice and shrimp production, due, in part, to climatic conditions driving changes in water quality, and pond management practices. However, the availability of natural benthic food supplies for shrimp production is less well studied. This study used a 15N‑nitrogen stable isotope tracer added to replicated enclosures within two rice-shrimp ponds to trace shrimp feeding on benthic natural biota. This experiment was conducted in both the wet and dry seasons. The 15N-ammonium rapidly enriched the 15N signature in the particulate organic matter (POM) in the water column, indicative of significant phytoplankton uptake of nitrogen (N). In contrast there was little enrichment of the benthic algae in the same time frame. After 13 d, most of the shrimp in the replicate enclosures had little or no 15N enrichment. This result occurred across both ponds and in both seasons. This suggests that enriched N was not transferred through the benthic food web to the shrimp. The results of the 15N enclosure experiments were combined with biomass estimates of benthic algae and macrobenthos, shrimp growth data, and linked to other parallel studies of water quality and sediment biogeochemistry in the same ponds. Overall, the findings point to inadequate feed stocks for shrimp, and hence the need to consider supplemental feeding with high quality formulated feeds in order to improve growth rates and survival. • 15N-tracers were used to show that natural food was limiting for black tiger shrimp in rice-shrimp ponds. • Low oxygen, high temperatures and variable salinity appear to have affected shrimp growth. • The combined effects of low food availability and poor water quality affected growth rates. [ABSTRACT FROM AUTHOR]