Ecological Associations of Littoraria irrorata with Spartina cynosuroides and Spartina alterniflora

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GENERAL WETLAND SCIENCE

Ecological Associations of Littoraria irrorata with Spartina cynosuroides and Spartina alterniflora Caroline Mackenzie Failon 1

&

Serina Sebilian Wittyngham 1

&

David Samuel Johnson 1

Received: 16 August 2019 / Accepted: 29 April 2020 # Society of Wetland Scientists 2020

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 sealevel rises. Keywords Brackish marsh . Mesohaline marsh . Salt marsh . Ecological equivalence . Sea level rise

Introduction Tidal marshes cover approximately 45,000 km2 globally (Greenberg et al. 2006) and contribute ecologically and economically to human well-being by providing erosion and flood control, recreation, improved water quality, carbon sequestration, and nursery habitat for commercially important fishes and invertebrates (Boesch et al. 2000; Beck et al. 2001; Shepard et al. 2011). There are 16,000 km2 of tidal marshes in North America alone, with high concentrations on the South Atlantic coast and Gulf of Mexico (Greenberg et al. 2006). The Chesapeake Bay in the United States contains an estimated 1240 km2 of tidal marshes, with brackish Electronic supplementary material The online version of this article (https://doi.org/10.1007/s13157-020-01306-4) contains supplementary material, which is available to authorized users. * Caroline Mackenzie Failon [email protected] 1

Virginia Institute of Marine Science, William & Mary, P.O. Box 1346, Gloucester Point, VA 23062, USA

marshes making up one-third of this area (Stevenson et al. 2000). A mesohaline marsh is a type of estuarine brackish marsh where saline and fresh waters mix, leading to salinities between 5 and 18 ppt on average (Odum 1988).