Biomass accumulation in those salt marshes can equal the productivity of Iowa corn fields, but we don't eat the grasses directly. There's another key set of statistics to consider as well, provided by the Weldon Cooper Center at UVA and the Federal government.
Poultry production involves a lot of labor.
It's nothing new for business to move to labor. The textile industry moved from New England to the Southern Industrial Piedmont after the Civil War to get cheap labor. Fries, Danville, Roanoke, and other Virginia communities south of the James were once home to high-wage manufacturing jobs associated with cotton. In the last decade, the textile companies moved their factories again. The factories closed throughout the region, and the jobs moved to Mexico and Asia where labor costs are even lower.