Eelgrass beds can occur both in the littoral and sublittoral zones of an estuary. Dwarf eelgrass (Zostera noltii) is found highest on the shore, narrow-leaved eelgrass (Zostera angustifolia) occurs on the mid to lower shore, and eelgrass (Zostera marina) predominantly in the sublittoral. These plants are an important source of food for wildfowl, particularly for brent geese (Branta bernicla) and wigeon (Anas penelope), which feed primarily on intertidal eelgrass beds and species of algae, notably Enteromorpha spp.