Giant kelp can be harvested fairly easily because of its surface canopy and growth habit of staying in deeper water.

Kelp ash is rich in iodine and alkali.
In great amount, kelp ash can be used in soap and glass production.
Until the Leblanc process was commercialized in the early 19th century, burning of kelp in Scotland was one of the principal industrial sources of soda ash (predominantly sodium carbonate).
Around 23 tons of seaweed was required to produce 1 ton of kelp ash.
The kelp ash would consist of around 5% sodium carbonate.

Once the Leblanc Process became commercially viable in Britain during the 1820s, common salt replaced kelp ash as raw material for sodium carbonate.
Though the price of kelp ash went into steep decline, seaweed remained the only commercial source of iodine.
To supply the new industry in iodine synthesis, kelp ash production continued in some parts of West and North Scotland, North West Ireland and Guernsey.
The species Saccharina latissima yielded the greatest amount of iodine (between 10-15 lbs per ton) and was most abundant in Guernsey.
Iodine was extracted from kelp ash using a lixiviation process.
As with sodium carbonate however, mineral sources eventually replaced seaweed in iodine production.

Alginate, a kelp-derived carbohydrate, is used to thicken products such as ice cream, jelly, salad dressing, and toothpaste, as well as an ingredient in exotic dog food and in manufactured goods.
Alginate powder is also used frequently in general dentistry and orthodontics for making impressions of the upper and lower arches.

Kelp polysaccharides are used in skin care as gelling ingredients and because of the benefits provided by fucoidan.

Kombu (昆布 in Japanese, and 海带 in Chinese, Saccharina japonica and others), several Pacific species of kelp, is a very important ingredient in Chinese, Japanese, and Korean cuisines.
Kombu is used to flavor broths and stews  (especially dashi), as a savory garnish (tororo konbu) for rice and other dishes, as a vegetable, and a primary ingredient in popular snacks (such as tsukudani).
Transparent sheets of kelp (oboro konbu) are used as an edible decorative wrapping for rice and other foods.

Kombu can be used to soften beans during cooking, and to help convert indigestible sugars and thus reduce flatulence.

Because of its high concentration of iodine, brown kelp (Laminaria) has been used to treat goiter, an enlargement of the thyroid gland caused by a lack of iodine, since medieval times.

In 2010, researchers found that alginate, the soluble fibre substance in sea kelp, was better at preventing fat absorption than most over-the-counter slimming treatments in laboratory trials.
 As a food additive, it may be used to reduce fat absorption and thus obesity.
Kelp in its natural form has not yet been demonstrated to have such effects.
Giant kelp can be harvested fairly easily because of its surface canopy and growth habit of staying in deeper water.
Kelp ash is rich in iodine and alkali. In great amount, kelp ash can be used in soap and glass production. Until the Leblanc process was commercialized in the early 19th century, burning of kelp in Scotland was one of the principal industrial sources of soda ash (predominantly sodium carbonate). Around 23 tons of seaweed was required to produce 1 ton of kelp ash. The kelp ash would consist of around 5% sodium carbonate. 
Once the Leblanc Process became commercially viable in Britain during the 1820s, common salt replaced kelp ash as raw material for sodium carbonate. Though the price of kelp ash went into steep decline, seaweed remained the only commercial source of iodine. To supply the new industry in iodine synthesis, kelp ash production continued in some parts of West and North Scotland, North West Ireland and Guernsey. The species Saccharina latissima yielded the greatest amount of iodine (between 10-15 lbs per ton) and was most abundant in Guernsey. Iodine was extracted from kelp ash using a lixiviation process. As with sodium carbonate however, mineral sources eventually replaced seaweed in iodine production. 
Alginate, a kelp-derived carbohydrate, is used to thicken products such as ice cream, jelly, salad dressing, and toothpaste, as well as an ingredient in exotic dog food and in manufactured goods. Alginate powder is also used frequently in general dentistry and orthodontics for making impressions of the upper and lower arches.
Kelp polysaccharides are used in skin care as gelling ingredients and because of the benefits provided by fucoidan.
Kombu (昆布 in Japanese, and 海带 in Chinese, Saccharina japonica and others), several Pacific species of kelp, is a very important ingredient in Chinese, Japanese, and Korean cuisines. Kombu is used to flavor broths and stews  (especially dashi), as a savory garnish (tororo konbu) for rice and other dishes, as a vegetable, and a primary ingredient in popular snacks (such as tsukudani). Transparent sheets of kelp (oboro konbu) are used as an edible decorative wrapping for rice and other foods.
Kombu can be used to soften beans during cooking, and to help convert indigestible sugars and thus reduce flatulence.
Because of its high concentration of iodine, brown kelp (Laminaria) has been used to treat goiter, an enlargement of the thyroid gland caused by a lack of iodine, since medieval times.
In 2010, researchers found that alginate, the soluble fibre substance in sea kelp, was better at preventing fat absorption than most over-the-counter slimming treatments in laboratory trials.  As a food additive, it may be used to reduce fat absorption and thus obesity. Kelp in its natural form has not yet been demonstrated to have such effects.
Kelp