Seaweed on a beach you visit is Bad.

Seaweed in the Ocean is Good.

https://www.google.com/amp/s/www.cbsnews.com/amp/news/seaweed-farming-and-its-surprising-benefits/

The article says having seaweed in the ocean is like planting trees on land wrt CO2.

http://www.foragingtexas.com/2011/11/sargassum.html?m=1

Sargassum is human edible and many sea creatures eat it.