The Marsh Periwinkle
Description Small top shaped shell. Globe like body whorl and sharp spire. Spire less than twice aperture length. Round or elliptical aperture (2).
Habitat Lives in brackish marshes in salt marshes on the east coast of the United States (2, 3).
Range New York to Texas (2)
Ecological Notes Closely associated with Spartina alterniflora. Herbivore, prefers to feed on tall-form Spartina because it is more rich in nitrogen and other nutrients but due to its predator, Callinectes sapidus (the blue crab), it is usually only found on short-form Spartina due to water levels not being able reach the short-form because it is higher in elevation than the tall-form (3). They can be found climbing up and down stalks of Spartina during the tidal cycle in order to avoid predation (1). They are the dominant marsh grazers and can control populations of Spartina by scaring them with their radula which causes death due to fungal infections(3). They also consume large amounts of fungal and algae biomass from the blades of Spartina (1). Females lay their eggs in floating capsules. The young are free swimming (2).
Personal When in the salt marsh of the outerbanks, Littoraria irrorata, could be seen climbing the Spartina. Many hermit crabs were also seen on the sand using the periwinkle's shell.
1) Long, W. C. (2007). Habitat size, flora, and fauna: Interactions in a tidal saltwater marsh. Journal of Experimental Marine Biology and Ecology, 353(1), 80-88.
2) Porter, H. J. & Houser, Lynn. Seashells of North Carolina. Raleigh, North Carolina: North Carolina Sea Grant College Program.
3) Silliman,B.R. & Bertness, M. D., (2002). A trophic cascade regulates salt marsh primary production. Proceedings of the National Academy of Sciences of the United States of America, 99(16). 10500-10505
Contributed by Tom Scott 2010