why are the supplements used by humans?
A supplement can provide nutrients either extracted from food sources or synthetic, individually or in combination, in order to increase the quantity of their consumption.
Dietary supplement
A supplement can provide nutrients either extracted from food sources or synthetic, individually or in combination, in order to increase the quantity of their consumption. 
what is manta ray? Large rays belonging to the genus "Mobula" what kind of creatures are they? They are classified among the Myliobatiformes (stingrays and relatives) and are placed in the family Myliobatidae (eagle rays). is it a kind of fish? No, they are large rays. where do they live? They are found in warm temperate, subtropical and tropical waters. how do they look like? They have broad heads, triangular pectoral fins, and horn-shaped cephalic fins located on either side of their mouths. They have horizontally flattened bodies with eyes on the sides of their heads. what impact does it create in tourism industry? Sites at which manta rays congregate attract tourists, and manta viewing generates substantial annual revenue for local communities. any specific region where they are widely seen? Indo-Pacific and tropical east Atlantic what is food habits like? They consume large quantities of zooplankton in the form of shrimp, krill, and planktonic crabs. In deeper depths, mantas consume small to medium-sized fish. what is the second one? Krill are small crustaceans of the order Euphausiacea. can humans consume it too? Krill are under development in the early 21st century as human food, dietary supplements as oil capsules, livestock food, and pet food.
wiki:25288289
Dietary supplement [SEP] Introduction
A dietary supplement is a manufactured product intended to supplement the diet when taken by mouth as a pill, capsule, tablet, or liquid. A supplement can provide nutrients either extracted from food sources or synthetic, individually or in combination, in order to increase the quantity of their consumption. The class of nutrient compounds includes vitamins, minerals, fiber, fatty acids and amino acids. Dietary supplements can also contain substances that have not been confirmed as being essential to life, but are marketed as having a beneficial biological effect, such as plant pigments or polyphenols. Animals can also be a source of supplement ingredients, as for example collagen from chickens or fish.