"The microfauna and microflora are food for the oysters, shrimp and larger organisms, as we all know, and if they are decimated, than the shore and larger marine faunas will also be decimated.
Moreover, will intake of these dispersants by food species cause illness to humans?"

This could be as true with no dispersants, as with dispersant use (and maybe even more so)? I suspect keeping the oil below the surface in a smaller place away from the coastal waters, coastlines and wetlands and dilluting the impacts in the deep waters is a major goal of dispersant use. I also suspect the cost (financial and reputation) would be much greater if the oil reaches the coast in great amounts.

It is always complex for fish harvesters to make direct linkages if catches lower. And, compensation costs for these folks are nowhere as high as potentially those on the coastlines. And, also initiatives, just may work....as they have elsewhere (under different circumstances, of course).