How do cross-ecosystem interactions affect Nantucket salt marsh food web structure and ecosystem functioning?

Submitted in fulfillment of a 2015 Nantucket Biodiversity Initiative grant

New England salt marshes are some of the most productive and important coastal ecosytems but they are currently under threat from human activities in adjacent terrestrial and marine habitats (e.g. eutrophication from terrestrial runoff and the removal of top predators). Recent experiments indicate that predators are likely key interactors along salt marsh creek banks but the identity and relative importance of common cross ecosystem predators are unknown and likely vary from marsh to marsh. Surveys in 2014 indicate that salt marshes of Nantucket host a diverse suite of predators including marine (e.g. green crabs, blue crabs, American eels, mummichogs) and terrestrial species, (e.g. shorebird predators such as Great Egrets, gulls, American Oystercatchers, Greater Yellowlegs, Willets, and Whimbrels). I used a combination of surveys, tethering experiments, and a manipulative field experiment to answer the following questions: (1) What are the most common predators of creek bank invertebrates in Nantucket salt marshes? and (2) What is the relative importance of shorebird and marine predators on the community structure and ecosystem functioning of Nantucket marshes? Preliminary results indicate that marine predators such as green crabs and blue crabs are likely keystone predators of marsh crabs, whereas bird predation is periodic. Marine predators have the largest affect on the marsh community, decreasing crab, mussel, and juvenile snail abundances. These same predators, likely green crabs and blue crabs and eels, also increase Spartina primary production. Determining the frequency and importance of cross ecosystem predators on creek bank processes will help understand how Nantucket salt marshes function and provision ecosystem services like erosion protection and nursery habitat availability.