The salt marsh amphipod, Gammarus palustris Bousfield, 1969 at the northern limit of its distribution: I. Ecology and life cycle

The ecology and life cycle of the American endemic Gammarus palustris were studied in salt marshes of Great Bay, N.H. at its apparent northern-most limit. The species is an obligate epibenthic inhabitant of the lower marsh, residing most of the year in a narrow zone limited shoreward near Extreme High Water Neaps. There is no off-marsh migration in winter. Zonation is complicated by a seasonal distributional cycle, and microhabitat preferences for Spartina alterniflora culms, grass blade junctions, Ascophyllum, rocks, and tidal debris, correlated with animal size within and between sexes, and related to temperature variation. The species is a detritus-aufwuchs feeder; larger adults eat some macroalgae. Embryonic development is relatively fast at temperatures above 10 °C compared to other Gammarus spp, reproduction is bivoltine, and females produce up to 3 broods per breeding period. Mechanical action of ice may influence population size. Microhabitat preferences of associated amphipod species are also discussed