The Distribution of Talitrid Amphipods (Crustacea) on a Salt Marsh in Southern Tasmania, in relation to Vegetation and Substratum

Supralittoral and terrestrial talitrid amphipods were collected from a salt marsh in Southern Tasmania by pitfall trapping along transects from the mid-tidal level to above the high-tide mark, and by hand collecting from sites chosen to represent the full range from salt marsh to terrestrial vegetation. At each site, the cover of all major plant species was recorded, and soil samples were collected from which soil moisture, organic content and salinity were measured. Eight talitrid species from four ecological groups were collected; one palustral species, one beachflea, three coastal landhoppers and three eastern forest landhoppers. There was substantial overlap in the distributions of these groups. The undescribed beachflea had the widest distribution, from the wettest, most saline sites to the Schoenus nitens tussock grassland at the extreme high-tide mark. The palustral species, Eorchestia palustris, overlapped substantially with the beachflea, but was found within a narrower band of salinities (though not in the most saline sites) and in more poorly-drained sites than the beachflea. Coastal landhoppers, Austrotroides maritimus, Keratroides rex and an undescribed species of Tasmanorchestia, were found mainly in the S. nitens tussock grassland, where they overlapped with forest landhoppers, Keratroides vulgaris, Mysticotalitrus tasmaniae and M. cryptus, which were found mainly in non-saltmarsh terrestrial sites, well above the high-tide mark. These distributions are discussed in terms of the likelihood that salt marshes provided the route by which talitrid amphipods colonized land. There is no reason from these data to reject salt marshes as the route to land, and it is suggested that they are a more likely route than via rocky or sandy shores.