Distribution and Morphology of Littoraria irrorata in Mesohaline Tidal Marshes Dominated by Juncus roemerianus

Marsh periwinkle snails ( Littoraria irrorata ) are common in salt marshes of the Atlantic and Gulf of Mexico coast and often occupy important ecological roles. Much of the published research examining the abundance and role of this species has been conducted in marshes dominated by smooth cordgrass ( Spartina alterniflora ). We investigated the distribution and morphology of L. irrorata in marshes dominated by black needlerush ( Juncus roemerianus ) an important marsh species that commonly forms monotypic conditions in more mesohaline conditions. Eight marshes along the coastal border of Alabama and west Florida, USA, were sampled for L. irrorata and other environmental data (plant density and biomass) at four different proximities to the marsh-bay edge. We also examined L. irrorata abundance, shell size, and biomass across a salinity gradient (quantified using a salinity regime index). We found that (1) abundance of L. irrorata in J. roemerianus -dominated marshes (1.0 ± 1.0 to 25.3 ± 12.6 snails m −2 ) were within the lower range of snail densities reported for S. alterniflora -dominated marshes elsewhere, (2) most L. irrorata were detected along the 10-m waterward edge of the marsh, and (3) considering snails at the waterward edge, a positive relationship ( r 2 = 0.53, p = 0.04) was detected between marsh salinity and snail density along with a negative relationship ( r 2 = 0.86, p < 0.01) between marsh salinity and mean snail shell length. Mechanisms associated with L. irrorata abundance and morphology are unclear but likely relate to various aspects of salinity and tidal connectivity. These results suggest that mesohaline J. roemerianus marshes may be marginal in terms of L. irrorata habitat; however, further research is encouraged.