TendOcean

You mean other than the fact that techniques for efficiently growing such amounts of seaweed do not exist? Of the amount produced globally today, 90% comes from China, Korea, Japan, and the Philippines and that production is all very labor intensive and done in locations and using methods that are simply not applicable to the United States.

There is a huge about of R&D needed to get any of this to scale. Some of it is already underway.

The "Transportation problem" can easily be overstated. If we assume AT is grown offshore to avoid the well-recognized conflicts of near-shore, then harvested material needs to get to shore for some form of processing and subsequent shipping to where the cows are. Given the super efficient nature of shipping goods over water (at least at low speed) at least the water portion of that route would be of little concern. Technologies are under development specifically for this purpose.

A bigger problem may be where AT can be farmed, since it is not native to US waters (except Hawaii) and permitting agencies are understandably strict about introductions.

That is probably an incorrect assumption. Corn farming requires land, fresh water, and fertilizer - all very expensive. Growing seaweed requires none of those things, only ocean space and a proper farm system.