"This is the sporophyte," she said at her lab in La Jolla, holding one of a dozen flasks filled with the red algae, dancing in aerated seawater. "In this case, the bubbles are not as vigorous, allowing these puff balls to get bigger.

"By just manipulating nitrogen and phosphorous, we have already seen that we can double the concentrations of bromoform in just a week," she added.

As commenters have noted previously, it seems like using synthetic bromoform would be cheaper and more scalable. The rest of the seaweed appears to be incidental to the methane suppression. But maybe there are regulations about introducing new cattle feed additives that you can sidestep by mixing whole algae into the food. Or maybe they're already developing this with consumer branding/marketing in mind; "seaweed" sounds better than "bromoform."