A typical coastal wetland in Maine has several different zones of vegetation based on the tides.

Low marsh, between mean low tide and mean high tide, is flooded twice daily by tidal action.

High marsh is flooded by above-average tides twice a month and irregularly by storm tides.

Pannes are shallow “ponds” in the high marsh that are flooded periodically by high tides. Deeper pannes that remain filled with water (pools) may contain widgeon grass (Ruppia maritima), sheepshead minnow, and mummichogs, providing a source of food for waterfowl.

Tidal channels, open water, and tidal flats are all important components of the marsh ecosystem. Tidal flats may support economically significant marine worm and clam populations.