Virginia Institute of Marine Science
The salt marsh periwinkle (Littoraria irrorata) is a common and often abundant mollusk in marshes of the Gulf and Atlantic coasts of the United States. Several studies have focused on the effects of periwinkles on Spartina alterniflora production and the effects of oil on periwinkle survivability, yet the general ecology of the snail has been underreported. In this study, we measured spatial distributions, biomass, shell repair frequency, and a suite of morphological characteristics of L. irrorata at three sites in each of five regions spanning the southeastern Louisiana Coast between the Atchafalaya and Mississippi rivers. Sampling was conducted along 50 m edge-to-interior transects in S. alterniflora-dominated marshes. We found that L. irrorata density, individual biomass, and total areal biomass significantly varied by region. Each also significantly varied with distance from the marsh edge, with the exception of total periwinkle areal biomass. We saw a general trend across most regions where periwinkle density tended to be greatest 10 m from the marsh edge and biomass tended to be greatest 20-30 m from the marsh edge; however, neither periwinkle density nor biomass was related to S. alterniflora density or stem height. The allometric relationship between shell length and biomass varied significantly between all regions, indicating that this species has differing regional growth patterns. A possible driver of these regional patterns in allometry is differences in predation pressures, with increased predation scaring at Port Fourchon sites corresponding to snails with larger shells yet less internal biomass per length compared to other regions. This study provides the first large-scale description of the spatial ecology and regional morphometry of the salt marsh periwinkle, an important organism in structuring salt marsh ecosystems, and suggests that the pressures exerted by L. irrorata on plant production found in other studies likely varies by geography and spatial location within a marsh.
Littorina-Irrorata Say; Horizon Oil-Spill; Spartina-Alterniflora; Littoraria-Irrorata; Organic-Matter; South-Carolina; Gastropod; Behavior; Biomass; Fungal
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Rietl, AJ; Sorrentino, MG; and Roberts, BJ, Spatial distribution and morphological responses to predation in the salt marsh periwinkle (2018). Ecosphere, 9(6).