Effects of moderate eutrophication on saltmarsh food webs

We examine the impacts of moderate nutrient enrichment on the production mummichog, Fundulus heteroclitus, as part of a 10-year whole ecosystem experiment in a Plum Island Sound saltmarsh. In the initial stages of nutrient enrichment we observed a classic bottom up stimulation response in fish production. However, after the first six years fish production declined rapidly. The mechanism for the decline is not known but we hypothesize indirect interactions with other saltmarsh consumers may play an important role, as well a habitat alteration. Our results demonstrate that long-term nutrient enrichment can have complex impacts on the production of saltmarsh fish that are not predictable by classic bottom up/ top down control theory. Our findings suggest that eutrophication and climate change induced sea level rise will have synergistic negative effects on the production of saltmarsh fish primarily through habitat alteration and loss. In 2016, we conducted a 15N tracer experiment to test the concept of bottom up vs creek edge and marsh platform control of mummichog production and have been processing and analyzing samples.