Seaweed are rich in protein, very rich in vitamins and excessively rich i trace elements. For people in the well nourished part of the world the last point is the most interesting.
All chemical elements are present in sea water and algae are famous for a unic capability to absorb and concentrate those we call trace elements. Land plants are not bad either, but the soil in which they are rooted does not contain more trace elements than the rock minerals from which it has been formed. And they have an enemy, which seaweed have not: man, who is the great threat to trace elements in our foodstuffs. For the first man impoverishes the cultivated areas by removing with his harvests nitrogen, phosphorus, and host of different trace elements, then, with fertilizers, he adds nitrogen and phosphorus, possibly lime and potassium but no trace elements. For the second we impoverish cultivated and virgin land wherever industries and motorism cause the acid rain that dissolves from the soil and removes all those elements which increase in solubility in acid environment.
Only the sea is unaffected. It is too huge and sea water is buffered, balanced, it will not be altered in its pH by mixing with acid rain. The simplest and most natural way for us to compensate the constantly decreasing level of trace elements in our land based foodstuffs is to eat regularily a suitable amount of food from the sea.