The use of marine plants in terrestrial agriculture probably goes back as far as the history of agriculture among coastal people. As far as we know raw seaweeds and seaweed products (e.g. liquid hydrolysates, products of composting, ash from burnt seaweeds) have been used for millennia (and are still used today) as animal feeds, supplements to animal feeds, soil conditioners, mineral sources and fertilizers or plant foods.

One very large use of seaplants in agriculture is the use of coralline algae (maërl) such as Phymatolithon calcareum and Lithothamnion corallioides as soil conditioners, trace element and mineral sources. They can also replace bone meal in some feed applications and ground maërl is useful for water filtration. These algae contain calcium and magnesium carbonates that comprise up to 80% of the wet weight. Maërl is dredged off the coasts of France (Brittany), England, and Ireland. Over 600,000 tons are harvested each year from live and dead deposits. The dried, ground product is favoured by organic farmers and horticulturists.