Impacts of wintering redhead ducks (Aythya americana) on seagrasses in the northern Gulf of Mexico

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). 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. 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. Time-lapse photography provided estimates of the abundance and feeding activities of the birds. Redhead ducks actively and regularly fed in all experimental areas; however, flock sizes were significantly smaller than previously recorded in Texas and south Louisiana. In general, there was little evidence of grazing effects on R maritima biomass. H. 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. Similar to conclusions from previously conducted studies, we found no evidence that waterfowl were overexploiting their seagrass food resources.