Sodium alginate is the sodium salt of alginic acid, which is a chemical substance. Generally used for thickening/anti-sedimentation/molding of food/beverage/beer, etc. Textile printing and dyeing is thickened with reactive dyes.

Trehalose is the name of a candy, which may contain a small amount of seaweed fragments, or it may be a colloidal candy made of alginic acid (not necessarily sodium alginate). Gelatin (pure animal glue) can be made without any mixture of alginic acid, because sodium alginate is quite expensive at present.