One potential use is co2 sequestration (if you sink it) as kelp grows way faster than trees (several feet in a day) It can also be a cheap livestock feed. And it can grow with very few input costs (no herbicide, fertilizer) all you need is an area of ocean, some ropes nets etc. And it will grow in winter. Theres a Canadian guy former fisherman who has been building a market for it as well. Often it can include mussels and oyster farms.