Insights into the long-term physical controls on estuarine food webs and implications for future change

Freshwater discharge is an important driver of coastal ecosystem productivity. We use a variety of approaches from stable isotope assessments of foodwebs to tracking coastal herring migration through estuaries into rivers to understand the freshwater to saltwater linkages in food webs. Preliminary results observed a strong influence of freshwater residency time on the contribution of benthic and pelagic production sources in the food web and a significant reliance on high marsh prey items with increasing inundation times for benthic consumers in our module. We infer that long-term changes in flow regime and inundation time will likely compress the influence of the riverine sources of production and increase dependence on high marsh and upland production sources.

     In the short term this will likely result in an increase in secondary productivity and enhanced connectivity between estuarine and coastal ocean food webs. However, if saltmarsh plants are unable to keep up with sea level rise the system productivity will decrease as productive marsh habitats are converted to open water. Migrating herring are an important anldrous species that couples marne and freshwater foodwebs.  We have found geographicly wide spread correlations between herring abundance and changes in temperature and discharge.  Additionally, we are examining the interannual variability of run strength in selcted rivers. Sanplain grasslands are also coastal ecosystems that are hotspots of coastal biodiversity. Sanplain grasslands are maintained by a variety of factors (disturbanc, fire, mowing) and their productivity is strongly influenced by environmental variability, including rainfall and nitrogen.