Photo Credit: John Turnbull
The bad news is that ocean warming and acidification are pushing seaweed into decline.
The good news is that seaweed farm production of 500 million tons by 2050 could consume 135 million tons of carbon (3.2 percent of the CO2 added to seawater yearly from greenhouse gas emissions). It could absorb 10 million tons of nitrogen (30% of that estimated to enter the ocean) and 15 million tons of phosphorus (33% of the total phosphorus produced by fertilizers). Seaweed takes in five times more carbon (the leading cause of ocean acidification) than most land-based plants.
https://www.aquaculturealliance.org/blog/seaweed-aquaculture-benefits/
https://phys.org/news/2019-02-underwater-forests-threatened-future-climate.html
The bad news is actually much worse than the good news. Corals, which support around 25% of marine species, are being bleached and dying off from ocean acidification and warming.
Not only that, but global warming is having a direct effect on fisheries, with a decrease of 2.8 to 12.1% by 2050 attributable to climate change. And, that is in addition to the continuing depletion of fish stocks by overexploitation.
https://www.britannica.com/science/coral-bleaching
http://www.fao.org/newsroom/common/ecg/1000505/en/stocks.pdf