The ecological role of the common salt marsh snail, Melampus bidentatus in its northern range, Maritime Canada

Abstract

The gastropod Melampus bidentatus, an abundant macroinvertebrate and omnivore-detritivore in eastern North American salt marshes, may be influential in marsh dynamics near its northern range limit (Northumberland Strait, Maritime Canada). Through sampling and field experiments, I examined details of and tested possible proximal mechanisms for the snail’s unrestricted within-marsh spatial distribution, and effects of its density on Spartina grass and fungal dynamics. Snail survival (using tethering assays) and movement (using mark-recapture trials) indicated that mortality was very low independent of marsh location and movement was random, both consistent with the snail’s distribution throughout a marsh. In manipulations of snail density, live Spartina grass tended to be temporally variable in the snail’s absence, whereas aboveground dead grass biomass and fungal biomass (as quantified via ergosterol content) tended to decrease with higher snail densities by the end of the plant growing season (September). Conversely, at the end of the fungal decomposition season (November), higher fungal abundance on stems tended to be associated with higher snail densities. Despite high natural variation and consequent low statistical power, results suggested that the snail may negatively affect live grass dynamics, contribute to processing of dead grass biomass, consume fungi, and possibly stimulate fungal growth. My study is an important contribution in determining the role M. bidentatus in Maritime Canadian salt marshes.