This seaweed does grow in the sea, obviously, however there isn't nearly enough of it in the sea to provide for the US (or worldwide, for that matter) cattle market.

Further, this particular seaweed is presently undomesticated – which means that of the various types of algal cultivation methods (rope culture, tumble culture, etc) no one has quite gotten down the best means of getting stable growth out of the strain. This is what we are working to do.

I meant that adding seaweed to a cow's diet seems unlikely to increase the demand on our limited fresh water supply. AFAIK, there's no risk in running out of seawater.

If you grow it in the sea, you're creating the transportation problem the poster was complaining about.

Sure, but that only leads to a fresh water problem if the chosen "solution" to the transportation problem is to grow seaweed inland.

From the article: "When added to cow feed at less than 2% of the dry matter, this particular seaweed completely knocks out methane production.".

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.