Ecological Associations of Littoraria irrorata with Spartina cynosuroides and Spartina alterniflora

Abstract

It is well-documented that marsh periwinkles (Littoraria irrorata) consume and inhabit smooth cordgrass (Spartina alterniflora), but their interactions with big cordgrass (Spartina cynosuroides) remain unknown. Plant communities in mesohaline marshes will change as sea-level rise shifts species from salt-intolerant (e.g., S. cynosuroides) plants to salt-tolerant (e.g., S. alterniflora) ones. Therefore, understanding how L. irrorata interacts with different habitats provides insight into this species’ generalist nature and allows us to predict the potential impacts of changing plant communities on L. irrorata. We show, for the first time, that L. irrorata inhabits, climbs, and grazes S. cynosuroides. We compared both habitats and found snails were larger, plant tissue was tougher, and sediment surface temperatures were higher in S. alterniflora than S. cynosuroides. Snails had greater survivorship from predators in S. cynosuroides than in S. alterniflora. Further, snails grazed S. cynosuroides more than S. alterniflora, evidenced by a greater number of radulation scars. Despite these differences, snail densities were equal between habitats suggesting functional redundancy between S. cynosuroides and S. alterniflora for L. irrorata. Our results indicate L. irrorata is a habitat generalist that uses both S. alterniflora and S. cynosuroides, which may allow it to gain an ecological foothold as sea-level rises.