There are both resident and transient fishes and crustaceans in the salt marsh. Many transients come into the marsh as juveniles and use the marsh’s surface as a protective refuge from predators as they grow. This “nursery” function is important for many of our commercially important seafood species. Other transients include larger predators that come into the marsh with the tide to feed along the marsh edges on the smaller organisms that venture too far from the protection of the marsh grasses. Many of the resident organisms feed on the aufwuchs, like the periwinkle, olive nerite, grass shrimp, hermit crabs and amphipods. Fiddler crabs like sandy patches in the marsh where they can come out into the air at low tide to feed on microalgae growing on the sand. During high tide, they stay in their burrows to avoid being eaten. Blue and gulf crabs are one of the major predators on the marsh, crushing the shells of many species to eat them, catching small fishes, and eating dead animals.

Try this site for the answer:

http://www.uwf.edu/rsnyder/ffnwf/salmars/sltmars.html

Pitcher plants live in fresh-water swamps.

Periwinkles live in fresh water.