Kelp found along the Atlantic coast can reach a length of 10 feet, but can reach 120 feet in the Pacific. Algin is a gel like substance made from kelp. It is used in dairy products, auto polish, glues, and some medical products. Some kelp such as edible kelp (Alaria esculenta) is quite tasty. Some people take kelp pills, which are a good source of vitamin C.
Red algae does not always contain red pigment, it occasionally contains other pigments. Surprisingly, some species of red algae can be found at depths of up to 600 feet.
Dulse, a deep red edible seaweed can be found all the way from New York northwards. It ranges from the mid inter tidal zone all the way to deep waters. Dried Dulse is used as seasoning, and it can also be eaten live in it's raw rubbery state.
Also, another edible algae is purple laver, it sprouts on rocks, pilings, shells, and other algae. Without it's purplish color it would appear similar to Sea Lettuce. The thin, transparent, and tasty Purple laver can be found from Maine to Florida.
Green seaweed, a common sight in many shorelines and open seas, are not often found in but freshwater (only 13% are marine.) Sea lettuce, an edible organism, is found all over the eastern sea coast, from Maine to Florida.