Periwinkles Don't Have a Preference
Check out this recent research published from WM undergraduate work at Taskinas Creek in 2018:
Ecological Associations of Littoraria irrorata with Spartina cynosuroides and Spartina alterniflora
by
Caroline Mackenzie Failon, Serina Sebilian Wittyngham & David Samuel Johnson
https://doi.org/10.1007/s13157-020-01306-4
This study demonstrates that the marsh periwinkle, Littoraria irrorata, uses both smooth cordgrass (Spartina alterniflora) and big cordgrass (Spartina cynosuroides) as habitat. Although plant tissues were tougher, sediment surface temperatures hotter, and predation higher in smooth cordgrass, snail densities were equal between habitats, indicating that periwinkles are habitat generalists.