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7.Many tons of macroalgae are harvested annually around the world, with China and Japan being the countries that excel in their consumption.However, macroalgae are used in many countries for very different purposes, namely for food or for domestic animals (feed), agriculture, and medicine because of their therapeutic properties.Human Food and Animal Feed Microalgae and macroalgae have been utilized by humans for hundreds of years as food, fodder, remedies, and fertilizers.Microalgae such as Arthrospira (formerly Spirulina, Cyanobacteria) have a history of human consumption in Mexico and Africa.The increasing worldwide use of macroalgae has led to them now being exploited in industry [2,12].Ancient records show that people collected macroalgae for food as long ago as 500 B.C. in China and one thousand years later in Europe.Macroalgae Uses Macroalgae offer a large number of possibilities for commercial use.7.1.

7. Macroalgae Uses
   Macroalgae offer a large number of possibilities for commercial use. Many tons of macroalgae are harvested annually around the world, with China and Japan being the countries that excel in their consumption. However, macroalgae are used in many countries for very different purposes, namely for food or for domestic animals (feed), agriculture, and medicine because of their therapeutic properties. The increasing worldwide use of macroalgae has led to them now being exploited in industry [2,12].
   7.1. Human Food and Animal Feed
   Microalgae and macroalgae have been utilized by humans for hundreds of years as food, fodder, remedies, and fertilizers. Ancient records show that people collected macroalgae for food as long ago as 500 B.C. in China and one thousand years later in Europe. Microalgae such as Arthrospira (formerly Spirulina, Cyanobacteria) have a history of human consumption in Mexico and Africa. In the 14th century the Aztecs harvested Arthrospira from Lake Texcoco [13] (Farrar 1966) and used it to make a sort of dry cake called “Tecuitlatl”, and very likely the use of this cyanobacterium as food in Chad dates back to the same period, or even earlier to the Kanem Empire (9th century A.D.). People migrating from countries such as China, Japan, and Korea, but also from Indonesia and Malaysia, where algae have always been used as food, have brought this custom with them, so that today there are many more countries all over the world where the consumption of algae is not unusual, including Europe [14].
   Sea vegetables, as they are known, are included in the menus of many Eastern coun- tries. On the contrary, consumption of macroalgae in Western countries was synonymous with penury. Macroalgae represent exactly the opposite of the foods that surround us today. They are a natural food that provides us with a high nutritional value and with low fat content. Although about 50% of the dry weight of macroalgae is carbohydrates, humans do not have the necessary enzymes to break these long molecules, so they are not absorbed by the digestive system, behaving like water soluble fibers. Macroalgae are extraordinary dietary supplements due to their high content of minerals, vitamins, and structural polysaccharides (fibers), which can facilitate intestinal transit and lower the cholesterol level in the blood [2].
   Seaweeds also have a long history of use as livestock feed. They have a highly variable composition, depending on the species, time of collection and habitat, and on external conditions, such as water temperature, light intensity, and water nutrient concentration. The results available on the effect of seaweed supplementation on rumen fermentation are controversial, with reports of increased, decreased, or absence of effects. To be extensively used in ruminant feeding, seaweeds are requested in large quantities [15].
   7.2. Agriculture
   The use of macroalgae in agriculture as fertilizers is one of the oldest traditional uses. Some Corallinaceae are used to correct the pH of acidic soils, while at the same time they increase the production of crops because they contribute certain elements such as magnesium, strontium, boron, and iron. Seaweed extracts contain several natural compounds (such as auxins, cytokinins, gibberellin, and others) that can improve plant development. There are many species of seaweeds, and their varied extracts have been tested to control different plant diseases and insects that cause damage to the plants. In general, there are different modes of action by which the seaweeds control plant diseases and insects. Plant pathology studies show positive results related to the effect of induced resistance in plant defense systems against pathogens by using seaweed extracts or their isolated compounds [15].