232 MARINE FISHERIES OF NORTH CAROLINA 



for growth. Accordingly, their distribution in the sea is limited to depths 

 to which sufficient light penetrates, as the majority grow on the bottom 

 attached to stones or shells. Most seaweeds are found along the shore 

 wherever there is a substratum for attachment, from the intertidal zone 

 to a depth of 300 feet or more in very clear water. In waters that are not 

 clear, they may grow no deeper than one or two feet below low tide line. 

 Coastal waters are relatively rich in nitrates, phosphates, and other nutrient 

 salts that come from the land by drainage, a circumstance of benefit to 

 seaweeds. 



In general, brown algae are plants of colder waters, especially the giant 

 kelps, abundant along New England and Pacific coasts. Green algae, though 

 common in cold waters, exist in greater variety in warm waters such as 

 those of Florida and the West Indies. Red algae are also of greater variety 

 in the tropics, and are believed to be able to grow at lower light intensity, 

 hence greater depth, than most browns and greens. In Florida, however, 

 some green species grow well at nearly 300 feet. 



Many seaweeds are seasonal or annual. Along the North Carolina coast, 

 for example, many of those present during summer are of sub-tropical 

 affinity and are replaced by a different flora with northern affinities during 

 winter. A few species may be present only during spring or fall. As a result 

 of the effect of Cape Hatteras as a temperature barrier, North Carolina is 

 the southern known limit (in winter) for a number of species common in 

 New England, and the northern known limit (in summer) for many species 

 abundant in Florida. 



Only the red and brown seaweeds are of economic importance. A few 

 of the greens ("sea lettuce," for example) are eaten, but they are not a 

 significant item of commerce. Bluegreen algae are not utilized as the indi- 

 vidual plants are microscopic. 



The principal economic uses of red and brown seaweeds and their ex- 

 tractives (phycocolloids) may be classified as follows: in foods, bacterio- 

 logical media, pharmaceutical preparations, cosmetics, several industrial 

 processes, dental and other molding compounds, fertilizers, and miscella- 

 neous other fields. Seaweeds probably have been used for food since pre- 

 historic times, while their use as medicine and fertilizer must have devel- 

 oped centuries ago, particularly in the Orient. The growth of science and 

 industry during the past 100 years has led to many additional uses of seaweed 

 extractives, especially in the more industrialized parts of the world. New 

 uses and new t3TDes of seaweed products are frequently announced. 



In America, dried seaweeds are eaten on a small scale in New England, 

 mostly by people whose ancestors came from the British Isles; and along 

 the Pacific coast, mostly by people of oriental origin. Powdered seaweed is 

 often used in so-called health foods, in stock feed, and as a condiment. 



