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.