While brown seaweeds can be found on coral reefs, they are not so abundant or varied as red or green seaweeds. Like other plants, seaweeds produce their own food through a process called photosynthesis. Why are seaweeds really not weeds?
Seaweeds have many benefits — they act as food and habitat for marine creatures; they provide vitamins, minerals, and fiber to people; used as a thickening agent; used as fertilizer, etc. This poses a risk to those who consume seaweed every day, as 1, mcg of iodine is the tolerable upper limit TUL for adults 6 , 8.
Hijiki seaweed has been found to contain remarkably high levels of inorganic arsenic, a chemical element that is known to greatly increase risk of cancer. Seaweed collects valuable nutrients from the water and rich soil found in freshwater bodies of water such as lakes and ponds.
These aquatic plants can transfer some of these nutrients to your garden, helping your plants grow and produce an abundance of fruit or flowers. They release oxygen through every part of their bodies.
Even though the waters at that depth may appear pitch-dark to human eyes, there is still sufficient light to allow the alga to photosynthesize.
In turbid waters, seaweeds grow only in the top, well-lit layers of water, if at all. Formerly it was thought that seaweed species had adapted to their habitat by having pigments that were sensitive to the different wavelengths of the light spectrum. In this way they could take advantage of precisely that part of the spectrum that penetrated to the depths at which they lived. For example, the blue and violet wavelengths reach greater depths. The red algae that live in these waters must contain pigments that absorb blue and violet light and, as a consequence, appear to have the complementary color red.
Experiments have since shown that this otherwise elegant relationship does not always hold true. Given that all the substances that seaweeds need in order to survive are dissolved in the water, macroalgae, unlike plants, have no need of roots, stems, or real leaves. Nutrients and gases are exchanged directly across the surface of the seaweed by diffusion and active transport.
In some species there is no meaningful differentiation, and each cell draws its supply of nutrients from the surrounding water. On the other hand, specialized cell types and tissues that assist in the distribution of nutrition within the organism can be found in a number of brown macroalgae.
Access to nitrogen is an important limiting factor in seaweed growth, particularly for green algae. The increasing runoff into the oceans of fertilizer-related nitrogen from fields and streams has created favorable conditions for the growth of algae, especially during the summer when it is warm and the days are long.
Omelette tamago-yaki with Nori 1 sheet of nori seaweed 3 eggs mirin sweet rice wine salt and sugar 1. Crack the eggs into a bowl. Add a little salt, sugar, and mirin optional and whisk everything together lightly with a fork. Heat a pan that has been greased with a tiny amount of fat, preferably one that has virtually no flavor of its own. Pour the egg mixture into the pan a little at a time over low heat. Place the nori sheet on the wooden surface and, using chopsticks or a wooden spatula, fold the set egg mixture together on itself several times to create a flat, layered omelette tamago.
Remove the omelette from the pan and press itinto shape with a bamboo rolling mat, which will imprint a nice surface texture on it. Different species of seaweeds avail themselves of a variety of strategies in order to grow. In sea lettuce Ulva lactuca , the cells all undergo division more or less randomly throughout the organism. Other species, among them several types of brown algae, have a growth zone at the end of the stipe and at the bottom of the blade; this is where an existing blade grows and new blades are formed.
The oldest blades are outermost, eventually wearing down and falling off as the seaweed ages. As a result, the stipe can be several years old, while the blades are annuals. This growth mechanism allows the seaweed to protect itself from becoming overgrown by smaller algae, called epiphytes, which fasten on to it. On certain seaweed species, the epiphytes are found overwhelmingly on the stipes, which can become covered with them, while the blades retain a smooth surface as long as they are young and still growing.
Finally, some types of seaweeds, such as bladder wrack Fucus vesiculosus and the majority of the red algae, grow at the extremities of the blades. The overall effect of seaweeds on the global ecosystem is enormous. It is estimated that all algae, including the phytoplankton, are jointly responsible for producing 90 percent of the oxygen in the atmosphere and up to 80 percent of the organic matter on Earth.
We can compare their output with that of plants by looking at the amount of organic carbon generated per square meter on an annual basis. Macroalgae can produce between 2 and 14 kilograms, whereas terrestrial plants, such as trees and grasses in temperate climates, and microalgae can generate only about 1 kilogram. The vast productive capacity of macroalgae can possibly be best illustrated by the fact that the largest brown algae can grow up to half a meter a day.
That amounts to a couple of centimeters an hour! Seaweeds are made up of a special combination of substances, which are very different from the ones typically found in terrestrial plants and which allow them to play a distinctive role in human nutrition. Most notably, the mineral content of seaweeds is 10 times as great as that found in plants grown in soil; as a consequence, people who regularly eat seaweeds seldom suffer from mineral deficiencies. In addition, marine algae are endowed with a wide range of trace elements and vitamins.
Because they contain a large volume of soluble and insoluble dietary fiber, which are either slightly, or else completely, indigestible, seaweeds also have a low calorie count. A wild strain of Chondrus crispus , or Hana-Tsunomata in Japanese, appeals to both the eye and the palate. This seaweed has a distinct crunchy texture and a milder taste than most other sea vegetables. Its flamboyant colors—pink, green, and yellow—are completely natural.
Marine algae possess a fantastic ability to take up and concentrate certain substances from seawater. For example, the iodine concentration in konbu and other types of kelp is up to , times as great in the cells of the seaweeds as in the surrounding water, and the potassium concentration is 20—30 times greater. On the other hand, the sodium content is appreciably lower than that of salt water. Depending on the species, fresh seaweeds are 70—90 percent water by weight.
The composition of the dry ingredients in the different types of seaweeds can vary a great deal, but the approximate proportions are about 45—75 percent carbohydrates and fiber, 7—35 percent proteins, less than 5 percent fats, and a large number of different minerals and vitamins.
Broadly speaking, the proteins in seaweeds contain all the important amino acids, especially the essential ones that cannot be synthesized by our bodies and that we therefore have to ingest in our food. Porphyra has the greatest protein content 35 percent and members of the order Laminariales the lowest 7 percent.
Three groups of carbohydrates are found in seaweeds: sugars, soluble dietary fiber, and insoluble dietary fiber. Many of these carbohydrates are different from those that make up terrestrial plants and, furthermore, they vary among the red, the green, and the brown species of algae. The sugars, in which we include sugar alcohols such as mannitol in brown algae and sorbitol in red algae, can constitute up to 20 percent of the seaweeds.
The seaweed cells make use of several types of starch-like carbohydrates for internal energy storage; again, these vary according to species. For example, the brown algae contain laminarin, which is of industrial importance as it can be fermented to make alcohol.
Norwegian winged kelp Alaria esculenta is appearing on the menus of top restaurants. Soluble dietary fiber, which is situated in between the seaweed cells and binds them together, constitutes up to 50 percent of the organism. Composed of three distinct groups of carbohydrates, namely, agar, carrageenan, and alginate, fiber can absorb water in the human stomach and intestines and form gelatinous substances that aid in the digestive process. Insoluble dietary fiber derived from the stiff cell walls of the seaweeds is present in lesser quantities, typically amounting to between 2 percent and 8 percent of the dry weight.
Cellulose is found in all three types of algae and xylan another type of complex carbohydrate in the red and green ones.
The primary mineral components in seaweeds are iodine, calcium, phosphorous, magnesium, iron, sodium, potassium, and chlorine. Added to these are many important trace elements such as zinc, copper, manganese, selenium, molybdenum, and chromium.
The mineral composition, especially, varies significantly from one seaweed species to another. Konbu contains more than —1, times as much iodine as nori. On average, dulse—a widely eaten red seaweed—is the poorest choice in terms of mineral and vitamin content but, on the other hand, it is far richer in potassium salts than in sodium salts. In general, marine algae are a much better source of iron than foods such as spinach and egg yolks.
Seaweeds contain iodine, although the exact quantities again vary greatly by species. The iodine content is dependent on where the seaweed grew and how it has been handled after harvest. Furthermore, the iodine is not evenly distributed, being most abundant in the growing parts and least plentiful in the blades.
In particular, the brown seaweeds contain large amounts of iodine. It is not known for certain why brown seaweeds contain so much iodine, but this is probably linked to their capacity for rapid growth. Iodide was found to act as the main antioxidant for this tissue. As non-vascular plants, seaweeds lack the true leaves, stems, roots and internal vascular systems most other plants use to take in water, so they absorb it through the surface of their leaf and stem-like structures.
For this reason, seaweed must constantly be partially or completely submerged. Jessica Martinez is a freelance writer from Clayton, North Carolina. As a homeschooling mom, she enjoys writing about education, child development and family issues. Martinez also enjoys researching and writing about subjects she loves: history, art, interior design, gardening and travel.
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