Effect of grazing by Canada geese Branta canadensis on an intertidal eelgrass Zostera marina meadow

Fishing Island, in Portsmouth Harbor on the Maine–New Hampshire border (USA), is the site of an intertidal eelgrass (Zostera marina L.) bed that is part of SeagrassNet, an international program for long-term seagrass monitoring. Eelgrass bed parameters of canopy height, percent cover, and aboveground biomass have been monitored quarterly since October 2001 using the SeagrassNet protocol. A flock of nearly 100 Canada geese Branta canadensis L. over-wintered at Fishing Island and grazed on eelgrass from January to April 2003, an event that had not been seen at this meadow in 2 decades of observation. Before Canada geese were present, eelgrass parameters demonstrated seasonal fluctuations typical of the region. During the grazing event, eelgrass parameters declined drastically, and biomass losses reached 680 g m–2 in parts of the meadow. SeagrassNet data demonstrated that eelgrass did not recover after the geese departed. Additional fieldwork conducted from February to July 2003 showed that eelgrass recruitment via sexual reproduction at Fishing Island was minimal, and vegetative recovery was impeded by Canada goose consumption of the plant meristems. Unlike studies in other locations, which show seagrass quickly rebounding from annual grazing events, eelgrass at Fishing Island showed little recovery from Canada goose grazing through July 2003