A shallow depression in a salt marsh where the marsh is poorly drained. Pannes occur in both low and high salt marshes. Pannes in low salt marshes usually lack vegetation, and the substrate is a soft, silty mud. Pannes in a high salt marsh are irregularly flooded by spring tides or flood tides, but the water does not drain into tidal creeks. After a panne has been flooded the standing water evaporates and salinity of the soil water is raised well above the salinity of sea-water. Soil water salinities fluctuate in response to tidal flooding and rainfall. Small pond holes occur in some pannes; the pond holes are usually deeper than the thickness of the living salt marsh turf, and the banks or ?walls? of the pond holes are either vertical or they undercut the peat. Salt pannes can be formed by ponding of water on the marsh surface, scouring of wrack or coverage by storm wrack, and possibly by ice scour. Salt panne formation appears to be favored by a mean tidal range of about 20-80 cm and are poorly developed in settings with a mean tidal range greater than 1.6 m.

Characteristic plants of a salt panne include the dwarf form (15 to 30 cm tall) of cordgrass (Spartina alterniflora), glassworts (Salicornia depressa and Sarcocornia pacifica), marsh fleabane (Pluchea odorata), salt marsh plantain (Plantago maritima ssp. juncoides), arrow-grass (Triglochin maritimum), spikegrass (Distichlis spicata), sea-blites (Suaeda spp.), and salt marsh sand spurry (Spergularia marina). High salt marsh communities that are dominated by the dwarf form of Spartina alterniflora appear to support larger, better developed pannes than marshes dominated by S. patens and Distichlis spicata. Widgeon-grass (Ruppia maritima) grows in the pond holes; fishes that may be permanent residents in large pond holes include mummichog (Fundulus heteroclitus) and sheepshead minnow (Cyprinodon variegatus).

The salt pannes on the south shore of Long Island are intensely used by feeding shorebirds. A characteristic butterfly of salt pannes is the salt marsh skipper (Panoquina panoquin) where the caterpillar feeds on spikegrass (Glassberg 1999).