Red Seaweed: Characteristics, types, properties and more

The Red Seaweed or Phylum Rhodophyta, is an important group of seaweed that includes about 7,000 species. They are characterized mainly by having a reddish coloration and by the lack of flagella. Therefore, they have restricted capacity to mobilize.

Red Seaweed . Carrageenan

As in the case of others  marine algae, the eastern countries , specially  China;  have benefited from the properties of red seaweed, employing them  for treatments to benefit health.

Hence, we invite you to read on,  to learn more about this peculiar species, its characteristics, types, properties and much more….

Red Seaweed  Overview 

Following we offer a summary about the main  topics regarding these plants

Environment and Ecosystem

Almost all red seaweed breed in the sea, but it is possible to find them in fresh water , and even some of them are terrestrial. They can grow freely or as parasitic forms;  feeding on brown seaweed   or on mussel shells and other gastropods.

There are macro seaweed  in this group ,  being many of them coralline, that secrete calcium carbonate. This substance causes  the creation of coral reef,  even they  are usually confused with the corals themselves.

This species usually lives in the littoral zone, near the continental border. Due to the pigments they contain, they are capable of absorbing sunlight at great depths, even much more than other types of seaweed. They grow more easily in tropical and temperate waters. Although there are very rare cases of red seaweed in polar areas, where there is a greater population of green and brown seaweed.


Most red seaweed are multicellular, although there are also unicellular ones; but they are not common.  The multicellular ones,  grow in the form of filaments or membranous lamina, similar to fine and branched cylinders in the form of small trees. They can also be seen as whole or divided sheets.

The talus, which is nothing more than the whole that forms the entire structure; can be  described as the concentration of a large group of filaments , up to 1 centimeter in length.

They have specialized structures such as rhizoids, which are equivalent to the roots of marine plants. Similarly,  they have a sort of tendrils , which are structures used to adhere to the branches of other seaweed, rocks or itself.

They have reproductive structures in the form of spores and gametangia, as well as secretory cells of chemical substances.

General Characteristics

Red seaweed or Rhodophytas are photosynthetic organisms that is  they are able to absorb sunlight ,and transform it into energy.

They possess rodoplasts  that contain chlorophyll a,  in addition to pigments such as phycoerythrin and  phycocyanin, which predominate over  the chlorophyll. These pigments give them  their  characteristic red color.

They  can’t displace by themselves, due to their total lack of flagella throughout their life cycle. Likewise, they don´t  have centrosomes or any other form of microtubule organization.

They secrete colloids, mainly agar-agar and carrageenan;   two substances that are quite used in the pharmaceutical and food industry.

Some red seaweed can be found in fresh water, but they are generally marine seaweed.  They grow in the tropical and subtropical zones, below the intertidal line.

Life Cycle

Red seaweed are found forming multicellular organisms, although  in few cases, they also present  unicellular form. These seaweed don´t have a standard life cycle, however it can be summarized in three different stages or phases:


This is a sort of seaweed that contain a pair of complete genetic reproductive organs,  that is; they don’t have gender. They reproduce by forming  spores or tetraspores  in the form of seeds. These beings contain four genetically identical cells, with a single set of genetic material.

Since these cells only contain half the genetic material necessary for their reproduction, they are called haploid spores;  which means «half».


These are haploid organisms, with only half of the genetic material. But unlike tetraspores, these are the feminine or masculine forms of red seaweed.

Gametophytes are responsible for the formation of both male and female sexual organs. The female ones are known as carpogonium and contain an egg. The masculine ones, are called spermantangia, and they don´t have  sperm, but flagella.


It is the third phase, where a Rodofite really forms. The cystocarps are a complete form, with genetic material from both parents. When finding an appropriate means, it will settle to give a new seaweed.

Classification of Red Seaweed

The red seaweed belong to the Plantae Kingdom, however, since they are complex organisms with a large variety; there are doubts in this regard. But , they remain in this classification so far.

The phylum is Rhodophyta, which in turn is divided into two sub-phylum: Cyanidiophytina and Rhodophytina. In this article we will talk only about the Rhodophytina class,  where red seaweed belong.

Sub-phylum Rhodophytina

This is the group  where we find the red seaweed . Its red color is the product of a pigment called phycoerythrin. They live mostly in the sea, although there are about 164 species of freshwater.

They are the most abundant seaweed in very deep areas, since their pigments can capture sunlight more than 100 meters deep. These pigments absorb the blue light and reflect the red, which gives them their coloration.

There are six sub-division, of this species:


They are distinctly multicellular seaweed, whose cells are distinguished by ultra-structural differences. The life cycle is digenetic and heteromorphic, with macroscopic gametophyte, initially uniseriate,  which becomes pluriseriate by diffuse growth. The genera  Porphyra, better known as nori  seaweed , is the most  outstanding specimen of this group


Microscopic filamentous seaweed, such as Erythrocladia, belong to this class. There are also  macroscopic pluricellulars indiduals in this group, such as the Compsopogon. They can live in fresh or marine water, and they reproduce by monospores,  formed by the oblique division of the cells.


This class contains 95% of the red seaweed,  and  it is constituted   by 5 subclasses and 29 orders. They present the most complex morphological types

These are their  most outstanding  characteristics;

    • They have a trigenetic life cycle, which  includes carposporophyte, gametophyte and tetrasporophyte.
    • They have connections between adjacent cells, using a protein plug, which works as a structure and intercellular communication path.
    • Post-fertilization cell fusion mechanism.
    • They provide substances of economic importance such as agar-agar and carrageenan
    • They have the main role for the creation of  coral reefs


This  type of red seaweed have  a single branched or starred chloroplast, with or without pyrene; which is their main difference respect others seaweed.  Their  Golgi apparatus is found in association with mitochondria and the endoplasmic reticulum. They have  floridoside , as a low molecular weight carbohydrate , and they  reproduce by cell division.


They are unicellular red seaweed, with a single chloroplast, highly lobed with a centered pyrenoid. The Golgi apparatus is associated with the nucleus, and they  reproduce by cell division.

Alimentation  Characteristics of Red Seaweed

Red seaweed are photosynthetic organisms, thus they obtain organic carbon in the presence of sunlight. However, they need a humid environment to survive. They take the inorganic compounds of aquatic soil,  and in conjunction with oxygen and sunlight, transform these elements into glucose and carbonyl sulfide or COs.

Thanks to  studies carried out with different  seaweed species, it has been discovered that they can also feed on certain bacteria, that inhabit the underwater soils.

Ecological Importance of Red Seaweed

Red  Seaweed  have huge ecological importance, since they secrete calcium carbonate. This compound has essentials properties for the creation of  tropical coral reefs. Actually, red seaweed are usually called coralline seaweed.

These corals  are produced,  because  calcium is deposited on the walls of the seaweed in the form of calcium carbonate.

Economic Importance of Red Seaweed

These marine plants  are considered  a source of food for future generations, due to their large amount of proteins and nutrients.  Likewise in the industrial area , red seaweed are used as the main material to make laxatives, thickeners for soups, jellies, ice cream and some desserts. They also serve as  clarifiers in the brewing industry , and for processing  dairy products.

In the manufacture of pharmaceuticals, textiles and cosmetics products, red seaweed also have a great importance. For the Elaboration of phycocolenoids, such as the Agar-Agar, which is very nutritious. They are used in many slimming products,and in some dietary dishes because they have low calories,  and produce a satiety effect. Above all they stimulate the digestive system, prevent constipation and help reduce cholesterol levels.

Now, as usual, we invite you to watch this video, where you will see red seaweed in their natural enviroment..

Properties  of Red Seaweed

Throughout history, seaweed have been part of the diet in the Chinese Culture. They contain big amounts  of nutrients, proteins, vitamins and fiber; which make of them  an essential  food.  In addition to these properties, they are also rich in vitamin K and calcium.

In countries like Japan, the cultivation of red seaweed like nori,  has been improved , perfecting their technique to make them grow quickly. In the United States, specifically in Maine, they are known for collecting  from their waters, the irish moss.

To know more about the properties of these seaweed, we can say that they have many advantages, for example:

Antioxidant Effects

Thanks to the  presence of compounds ,such as  vitamins and minerals; these seaweed have antioxidant effects that protect the body from free radicals.

They are also a potent antiviral; especially because of the carrageenan, which strengthens the immune system, and protects the body from diseases caused by viruses and bacteria. Above all, it doesn´t create side effects, or addictions as  other types of drugs.

Iodine Effects

They are effective in the treatment of Goitre, because of their enormous amount of iodine; which restores the functions of the thyroid. Although in these cases,  it is important to maintain control with medical checkups and laboratory tests  frequently.

Note that a radical increase of  this mineral in the body, can generate adverse effects than those you are looking for. It can also generate serious problems associated with the digestive system, skin among others.

Effects Against Hypertension

For people with problems of  hypertension, it is very beneficial to consume  supplements based on red seaweed. In many studies conducted by Korean laboratories, it was found that this species of seaweed, has an inhibitory effect on the enzyme angiotensin-1;  which is  responsible for the increase in blood pressure.


900 milligrams of calcium per day,  are recommended  for the treatment of osteoporosis. Given the large amount of this mineral, contained in red seaweed; they are effective for  supplying quantities of calcium.

However, excess of calcium can cause damage to the body , as digestive disorders such as constipation, gas and bloating. Also consuming much of this mineral can severely affect the kidneys, by forming   stones and obstruction of the veins.

Vitamin K

Vitamin K is quite beneficial to improve bleedings. Among its properties, we could mention that it helps forming clots to stop this type of complications.

Converselly  excess of vitamin K,  could  be harmful for people with heart problems and prone to heart or brain vascular attacks.

The recommended daily consumption is 80 mg, for those people who don´t  have the mentioned complications.

Now we have another video for you, so you can learn about all the characteristics and properties of Red Seaweed…


Uses of Red Seaweed in Cosmetics

Since the beginning of the 20th century, the use of marine seaweed has been incorporated in the cosmetic industry, especially in France. The first steps were the development of soaps, shaving creams, shampoos, dyes, lipsticks, makeup and endless products for daily care.

In a short time, the use of seaweed in cosmetics products- had great demand; due to their  antioxidant properties, slimming, trace elements among others. They are also beneficial for skin care,  especially diatoms algae  which are also excellent.

In this sense, red seaweed have played a very important role in this industry. Over the years , its complex system has been discovered ,especially the big  number of substances and components, that make of them an almost miraculous species. They are quite useful for health, and for beauty in general.

These seaweed,  because of their high content of carrageenan, chlorophyll, phycobilin, mucilage, mineral salts, agar and carotenoids,  are widely used in the production of moisturizing and protective products; as a texture modulator.

They are also used as an anti-inflammatory, emollient and reduces the intestinal absorption of lipids and carbohydrates.

Cosmetic benefits of red seaweed

The cosmetic use of red seaweed, has two levels of industrial use. These are:  The preparations of plant extracts of these seaweed as active agents. On the other hand, the use of phycocolloids as gelling agents ,to give texture to creams and beauty products.

Uses as active agents

Due to the chemical structure of red seaweed; they have active agents that have moisturizing, toning, softening, draining, antioxidant and nourishing properties. Their  use in cosmetics and their  effects, vary according to the degree of concentration of each product.

 They are depurative: since they stimulate circulation and promote the elimination of toxins.

Moisturizing effects: This is a property of  all seaweed  in general, since they release a gelatinous substance that provides a quantity of water to the dermis.

They are nutritious: they contain carbohydrates, lipids, minerals and trace elements; all of them  very important for the good health of the skin.

Toning:  They provide minerals, that  increase the elasticity and tone of the skin decreasing its sagging.

Uses of Phycocolloids

Most seaweed,  and especially brown and red seaweed, contain polysaccharides such as phycocoloid, which gives them flexibility and mobility within the water. These conditions are usable for  certain products , giving them texture and gelatinized effect.

The most important phycocolloids present in red seaweed are:

Agar and carrageenan: These are two polysaccharide hydrocarbons, that are extracted from the cell walls of these seaweed. Both have suspension , emulsifying, stabilizing and gelling properties. The first is used to prepare cultivation media since they have great gelatinizing power. They can be sterilized without losing this capacity.

    • In the food area, the agar is also used to give a gelatin texture, as a stabilizer for the cheeses and to give consistency to the jams
    • In  the pharmaceutical industry, it is widely used as a cover for pills that can’t be dissolved directly in the intestine.
    • In the textile  this compound is  commonly used to shape the fabrics.
    • In photography and painting, as glue and base for oil paintings.
    • Carrageenan, on the other hand, is used as a thickener and gelling agent in the production of dairy products, textiles, cosmetics and aerosol bars, among others.

 Most Common Red Seaweed

Among the great variety of classes that  belong to this species of seaweed, the preferred ones in   the cosmetics industry are:

 Gracilaria Verrucosa: this is a species of red seaweed, very rich in agar-agar,  providing approximately 65% ​​of the amount of this product worldwide.

Asparagopsis Armata: it is very rich in carrageenan and minerals such as iodine, magnesium and silicon. It is used to create moisturizing and regenerating products. Likewise, it is used in creams for sensitive skin; especially for baby use and shaving creams, such as ladies’ hair removers, for its soothing and anti-inflammatory effects.

Palmaria Palmata: contains minerals such as chlorine, potassium, calcium, sodium, magnesium and phosphorus. It Also has mucilages and amino acids, very appropriate for moisturizers, anti-cellulite creams and heavy legs.

Corallina oficinallis:  It is used in cosmetics for the couperose and heavy legs ,due to its vaso constrictive properties.

Red Seaweed in aquariums and fish tanks

When you decide  to have your  own aquarium at home, probably you will select seaweed according to your particular likes. However, some of them grow spontaneously, especially the red seaweed;  which  reproduce like filamentous forms on substrates and rocks.

The species most likely to get in these spaces, is the brush, from  the genus Audouinella . They have a series of strands of short length,  colored in  dark brown,  even black sometimes; very similar to the strands of a brush,  which is the reason of their name .

Causes of red seaweed appearance  in aquariums or fish tanks

They are difficult to control and their causes are very varied;

    • The use of a great power pump, to filter the aquarium water, which  causes strong currents that stimulate the formation of brush seaweed.
    • Waters with low CO2 content and a high degree of alkalinity ,are also the focus of crops of  red seaweed.
    • High carbonate hardness and lack  of hygiene or maintenance.

Control Methods

Although there will always be seaweed in the aquariums;  there are some  measures  you can   ake to control them;

    • Keep  the aquarium with soft water and a high degree of acidity. Above all add CO2 using the appropriate methods for these ecosystems.
    • Eliminate if possible, by cutting the leaves with your hands or a pair of scissors; those that are stained and affected in some way.  This practice   avoids the proliferation of undesirable seaweed,  and also possible bacteria and fungi.
    • Place fish that feed on seaweed  in your aquarium, . you can ask in specialized sites. However, the species Crossocheilus siamensis is the most effective.
    • Decrease the power of the pump to a smoother filtering system.

Red Seaweed and Red Tides

Red tides are  produced by an increase of tiny red seaweed; that cause changes in the natural color of the seas.

Among the organisms responsible for these tides, we find the dinoflagellates; which  are able to synthesize powerful biotoxins.

The main cause of its appearance are the lack of wind, pollution, high temperatures or the presence of organic substances in the water that favor its extraordinary growth. However, they usually disappear spontaneously by decreasing the amount of oxygen, nutrients and predation.

Types of toxins and  their effects on the organism

The most common  type of toxins  in these tides  are: the amnesic, the stun and the gastric.

When consuming seafood during the season of red tide, the following symptoms may occur:

    • Tingling in the lips, tongue and face.
    • Paralysis in the face, shortness of breath, nausea, dizziness and vomiting.

These symptoms may appear after 30 to 60 minutes,  and according to the degree of concentration they can be deadly.

The type of toxin depends on the dinoflagellate, and up to now,  there are not known antidotes to suppress its effects. However, during these episodes of poisoning, the vomit can be induced, providing then warm salt water.

In extreme cases, where the person cannot breathe, the best action  is  to perform artificial respiration.  Then take the person to the nearest health center.

It is important to highlight that intoxication only occurs by ingestion and not for accidentally handling seawater.

Now,  following our  tradition of providing the best information, we invite you to watch this video about Red Tides…

Galicia: A significant experience

Galicia is one of the few places in the world which have managed to control the red tide. It is known as a big exporter of  marine products.  Galicia is also an example in the monitoring of red tides ,to offer a quality product without risk of contamination.

As a control method, they make two toxins tests to mollusks. They also  make constant studies to check the levels of dinoflagellate, which are the main  responsible of red tides.

With this dual system, they guarantee that the marine products they trade, are totally free of toxins.

In addition, they can anticipate possible infections to consumers, since they know when to close the fishing season.

In this way, they avoid having to dispose a significant amount of mollusks that are not  suitable for human consumption.

All these mechanisms make Galicia, not only an example for the rest of the world , to help provide security in their food; but also provide a maintenance of its coasts and areas surrounding.

It is such a safe system, that in strong episodes of red tide, the Galician mollusc will always be reliable and free of toxins.

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