(For anyone else curious, short story is they're basically multicelular algae)
Farming seaweed is not that complicated and is pretty widespread.
> Today, seaweed makes up nearly 30 percent of the wet weight of all seafood produced by aquaculture globally. About half of cultivated seaweed is red algae and about half is brown; of the brown, most is kelp.
https://hakaimagazine.com/features/banking-on-the-seaweed-ru...
There's also a company called Running Tide "farming" seaweed explicitly and exclusively as a carbon sink technology. Kelp is grown on rafts until it gets heavy and sinks to the ocean floor where it nourishes micro- and macrobiota.
Dulse flakes, laver, kombu, and a few others are available from Maine Coast Sea Vegetables Inc., for one, and if Bren Smith (aquaculturist and author of Eat Like a Fish) has his way, there will be more and cheaper seaweed available soon. I've eaten seaweed since I was a kid (mom grew up near the ocean), and sometimes add a few strips to black beans in the InstantPot for the flavor (again, my mother's influence). My family doesn't seem to mind.