In the past, large grazers such as green turtles, manatees and waterfowl likely had important controlling influences on seagrass communities however, as a result of human exploitation and loss of habitat, populations of many larger herbivores have dwindled to the extent that in some locations they are functionally extinct (Thayer et al., 1984 Valentine and Heck, 1999 Jackson et al., 2001 Valentine and Duffy, 2006). and Valentine, 2006 Valentine and Duffy, 2006).
Although researchers previously thought that seagrass was infrequently grazed, evidence suggests that grazing has played an important role in both historical and modern food webs of seagrass meadows (Heck Jr. et al., 2003), sequester significant amounts of carbon (Duarte et al., 2005) and stabilize sediments (Orth et al., 2006). As a large source of primary production in coastal ecosystems, seagrasses provide forage for large vertebrate and invertebrate herbivores (Valentine and Duffy, 2006), act as nursery grounds for juveniles of economically important finfish and shellfish (Beck et al., 2001 Williams and Heck Jr., 2001 Heck Jr. Seagrass beds are among the most diverse and productive coastal ecosystems and are universally recognized for the high value of their ecosystem services (Costanza et al., 1997 Orth et al., 2006 Valentine and Duffy, 2006). Similar to conclusions from previously conducted studies, we found no evidence that waterfowl were overexploiting their seagrass food resources. wrightii biomass followed expected seasonal patterns in both grazed and ungrazed treatments, and while both grazed and ungrazed biomass increased over the two years of the study, greater biomass increases occurred in ungrazed treatments. In general, there was little evidence of grazing effects on R maritima biomass. Redhead ducks actively and regularly fed in all experimental areas however, flock sizes were significantly smaller than previously recorded in Texas and south Louisiana. Time-lapse photography provided estimates of the abundance and feeding activities of the birds. We measured the impact of redhead duck ( Aythya americana) foraging on mixed shoalgrass ( Halodule wrightii) and widgeon grass ( Ruppia maritima) beds using caging experiments (1.5 × 1.5 m) at three locations in the nGOM. Seagrass meadows provide critical habitat for commercially important finfish and shellfish and as winter waters continue to warm, the nGOM will likely become increasingly appealing for wintering waterfowl. While it has been well established that waterfowl can sometimes control the distribution and abundance of seagrasses, relatively little is known about their effects in the northern Gulf of Mexico (nGOM).
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