Seagrass (Zostera spp.) as food for brent geese (Branta bernicla): an overview

Abstract 

Brent geese (called brant in North America) are among the smallest and the most marine of all goose species, and they have very long migration routes between high Arctic breeding grounds and temperate wintering grounds. Like all other geese, brent geese are almost entirely herbivorous. Because of these ecological characteristics they have a high food demand and are strongly dependent on stopover sites to ”refuel” during the migration period. Three subspecies of brent geese are distributed around the Holarctic, forming seven populations with distinct migration routes. Most or all of these populations make heavy use of Zostera spp. during migratory stopovers on spring and/or autumn migration. Examples of Zostera stopover areas being used by large numbers of brent geese for several weeks each year are Izembek Lagoon (Alaska), lagoons in Baja California, the German/Danish Wadden Sea, the Golfe du Morbihan (France), British estuaries, and the White Sea (Western Russian Arctic). Brent geese feed on Zostera wherever they can, but they can only reach the plants at low tide or in shallow water. Changes in Zostera abundance affect brent goose distribution, and the ”wasting disease” affecting Atlantic Zostera stocks during the 1930s was at least partly responsible for a steep decline in brent goose population sizes on both sides of the Atlantic. While Zostera is of outstanding importance as food for brent geese, the impact of the geese on Zostera stocks seems to be less important – at many sites, the geese consume only a small amount of the available Zostera, or, if they consume more, the seagrass can regenerate fully until the following season.