[colechristensen]

There’s really no need. Ever heard of an algal bloom? Also happens with jellyfish. On freshwater plants like duckweed do similar things.

Given the right nutrients population explosions happen. Environmentalists usually treat these as bad things but they certainly could be good ways to sink carbon. They could be triggered by fertilizing some of the more barren sections of ocean selected to minimize ecological effect. Quite a lot of the biomass simply falls to the ocean floor and gets buried, it could also be harvested and sequestered another way or used as a biomass fuel.

On freshwater lakes you could grow and harvest duckweed.