Dissolved material in sea water that is resistant to bacterial attack. Its name comes from the yellow color it imparts to the water. Brown algae, the principal algae group growing in coastal waters of temperature and higher latitudes, excrete phenolic compounds. These polyphenols are converted into a brown polymer by secondary reactions with carbohydrates and proteins of algal origin. The properties of the resulting substance are identical with Gelbstoff. Its concentration in sea water is around 1 mg/l and it is removed mainly by precipitation since its phenolic nature renders it resistant to bacterial attack. This is also known as yellow substance or gilvin.