The effects of temperature and flooding duration on the structure and magnitude of a floodplain prey subsidy

Riverine floodplains serve as an important link between terrestrial and aquatic systems, as the rising and falling of water drive spatial food web subsidies that are critical to the functioning and stability of ecosystems. As these systems are increasingly impacted by hydrological alterations and climate change, it is important to understand how floodplain spatial food web subsidies may respond to changing environmental conditions. Here, we examine the interannual variation in the structure of a sunfish (Lepomis spp.) prey subsidy from freshwater marshes into the mangrove-lined creeks of Rookery Branch in the Florida Coastal Everglades that occurs during seasonal dry downs. We evaluate how the structure of this subsidy relates to prior temperature and hydrological regimes based on a 16-year electrofishing dataset. We also characterise the intra-annual relationship between marsh water depths and sunfish migration patterns that underlie this subsidy. We found that interannual variation in the abundance and diversity of the sunfish prey subsidy was best explained by the minimum water temperature occurring within 90 days prior to peak abundance sampling periods, with lower minimum water temperatures associated with higher sunfish abundance and diversity. In contrast, interannual variations in the biomass of the sunfish prey subsidy were positively related to marsh flooding duration over 30 cm depth during the prior wet season. Intra-annual models estimated peak sunfish abundance and biomass values in riverine habitats to occur during the transition between wet and dry periods when marsh depths are between 10 and 15 cm. Multivariate analysis of community abundance and biomass composition revealed that minimum water temperatures played an important role in structuring the prey subsidy, while the effect of flooding duration was weak. These results provide important insight into how floodplain prey subsidies may be altered under future climate and hydrological regimes and inform ecosystem-based water management decisions.