Seaweed in perfumery is less about a literal shoreline smell than a marine material or accord built around salty, green, mineral and sometimes lightly iodine-like facets. It can give a fragrance a cool, damp texture and an unmistakable coastal character, with its effect shaped strongly by the surrounding notes. Depending on the formula, it may feature in the opening or heart.
In women's fragrances, seaweed commonly appears alongside citrus, watery notes, transparent florals, driftwood-style woods and clean musks. These pairings can keep it airy and bright, or make it darker, more earthy and atmospheric. Look here if you enjoy marine scents with more texture than a straightforward fresh aquatic, for daytime wear or a relaxed evening setting.