Hydrological connection links zooplankton communities and improves juvenile Chinook salmon growth in intertidal wetlands

Many once coupled habitats are now disconnected due to human infrastructure that prevents not only the transfer of organisms but also fundamental ecosystem processes. Here we investigate the importance of hydrologic connectivity between remnant floodplain and freshwater intertidal marsh habitats for zooplankton metacommunity dynamics and juvenile Chinook salmon growth in the Sacramento-San Joaquin Delta, California, U.S.A. Hydrological connection led to highly similar zooplankton communities between habitats. Further, we found that connected intertidal marsh habitats had approximately twice the total abundance of zooplankton of upstream floodplains and, in some cases, 15 times greater abundance than during disconnection. Gut content analysis demonstrated that salmon in our study utilized these abundant and high-value zooplankton food resources which likely contributed to elevated juvenile salmon growth rates in connected intertidal marsh habitats, where salmon had 25% greater growth rates (mm day-1) than those reared in disconnected marsh habitats. Additionally, salmon growth rates and condition factors were, in some instances, greater in connected intertidal habitats than upstream floodplains. These results provide strong evidence for the importance of connectivity for meta-community dynamics as well as productivity in historically coupled ecosystems and provide important information for future management and restoration.