All you can eat: multiple organic carbon sources fuel macroinvertebrate consumers within floodplain rivers in Australia's wet/dry tropics

Floodplain rivers in Australia’s wet/dry tropics constitute a vast region of pristine freshwater habitat, for which scant ecological knowledge exists. These systems experience flow variability outside the seasonal variation typically associated with tropical rivers and often cease flowing in the dry season, creating variation in hydrological connectivity. Consequently, their aquatic food webs may not be described fully by traditional conceptual models developed for tropical or temperate rivers. Therefore, the origins and use of organic carbon sources by dry season macroinvertebrate food webs within waterbodies of two northern river systems were investigated using stable isotopes analysis. Aquatic sources, especially algal, were clearly important as a food source for primary and secondary consumers, irrespective of their functional feeding group. Coarse detritus from local riparian plants was also an important carbon source for some consumers. However, consumers were often shown to rely on more than one basal source as their main form of assimilated organic carbon. Moreover, variation in hydrological connectivity among waterbodies was not matched consistently with relative source importance. Results show that these food webs exhibit resilience against natural disturbances like hydrological variability, a salient feature of these river systems and one common to floodplain river systems that are relatively undisturbed.