The Japanese have been farming seaweed as suggested in the article for decades, if not centuries.
From a
permaculture perspective, farming the oceans is all about creating edge... yes to artificial reefs... the zone along the shore and shallows are the most productive regions. Any solid structure provides the foundation for an entire food chain.
I use to fish a lot in the great south bay off long island. They made some artificial reefs out of used tires chained together and sunk in the bay (scary toxins?). The productivity of these structures was stunning in relation to the rest of the mostly flat-bottomed, sandy bay. We would catch crazy amounts of blackfish there.
Seaweed and algae are some of the most nutritious foods on earth, and also among the most efficient in terms of turning sunlight into food. Sea veggies also do not have the problems that animal seafoods do in terms of bioaccumulation of toxins higher up the food chain.
You see most of the problems with toxicity in top predators like tuna & dolphins... of course, shellfish that filter shallow waters near cities are going to be toxic.
Stacking functions, we would look at offshore wind & wave farms providing structure for a polyaquaculture including both sea animals and sea vegetables. Don't know if any seabirds are worth eating.