Red algae, the Rhodophyta, are an important source of food which includes nori and many other things, in Asia. In Asia, the high nutrient value of these foods, which includes vitamins and other minerals, makes them so much popular. The cultivation of these foods obtained from Red Algae is often very simple, which began in Japan around 300 years ago. How do red algae become an important source of food in Asia, and how are they red in color? These are some of the most important questions associated with Red Algae, and we are going to answer all of them in this article. In this article about red algae, we are going to study them in detail, where we will learn about their habitats, importance, food cycles, reproduction pattern, and many other important aspects.
Red Algae: Introduction
Red Algae belongs to the division Rhodophyta, which is one of the oldest groups of the eukaryotic algae found on earth. The name Rhodophyta is taken from the Greek language where 'rhodon' in ancient Greek resembles a rose, and 'phyton' resembles 'plant'. Therefore, we can see that Rhodophyta is the name given to Red Algae species because of their reddish color. The Rhodophyta also comprises over 7000 currently recognized species (with all the ongoing revisions in taxonomy), and it is one of the largest phyla of Algae. The majority of species (approximately 6800) from the Rhodophyta division are found in the 'Florideophyceae' class, and most of them consist of marine algae with the multicellular division, which even includes many notable seaweeds (a type of seafood). The unique thing about the Red Algae from their Rhodophyta division is that they are often found attached to the other shore plants. As we have already discussed, the taxonomy of this Rhodophyta group is still ongoing; therefore, the organization of this division may not correctly represent the evolutionary relationship (phylogeny) between the members of this division. In most species of the Rhodophyta division, continuity between the cells is provided by the thin protoplasmic connections.
Red Algae: Group
If we look at the scientific classification of the Red Algae, we will find that the division and taxonomy of this species is much disputed and still going on. Red Algae belongs to the domain Eukaryota where they form a distinct group that is characterized by species having eukaryotic cells without centrioles and flagella. This group of red algae species has chloroplasts that contain stroma (unstacked) thylakoids and lack endoplasmic reticulum, and most of the red algae use phycobiliproteins as their accessory pigments. We all have heard of the coralline algae, an algae species which plays a major role in building coral reefs and secreting calcium carbonate; this algae species belongs to the red algae group.
Red Algae: Colour & Appearance
The reddish color of Red Algae species is because of the masking of chlorophyll in them by the phycobilin pigments, which include phycocyanin and phycoerythrin. The pigment phycoerythrin from the Red Algae reflects red light and absorbs blue light, which makes them appear red in color. This happens because of the marine habitat of the Red Algae, where blue light penetrates water to a greater depth than the light of longer wavelengths. The pigments present in the Red Algae allow it to live and photosynthesize somewhere at greater depth than where most algae are usually found. Some of the algae from the Rhodophyta division have very little phycoerythrin pigment present in them, which in turn make them appear blue or green in color due to the chlorophyll present in them.
Red Algae: Distribution
Red Algae may be abundantly found in the marine environment, but they are relatively found very rare in freshwater habitats, and only 5% (approximately) of them occurs in the freshwater environment, which is contrasting to their occurrence in the marine habitats. Even in the occurrence of Red Algae in a freshwater environment, most of them are found in large numbers near the warmer areas. Except for the two species from the asexual class 'Cyanidiophyceae' of division Rhodophyta, i.e., coastal wave dwelling species; no terrestrial species of Red Algae have been found till now. The major reason behind this is considered as their evolutionary bottleneck when the last common ancestor of this species has lost much of their plasticity and 25% of their core genes.
Red Algae: Reproduction pattern
The reproduction pattern can vary in different species of Red Algae, which depend upon many factors. The reproduction cycle of all algae species belonging to this red algae group is usually triggered by the factors such as day length, sunlight, etc. Red Algae can reproduce asexually and sexually as well, and it all depends upon the environment and external factors around them. Asexual reproduction in the red algae can occur by vegetative means, which includes cell division, fragmentation, and propagules production, and through the production of spores by them.
Red Algae: Morphology
The study of the morphology of Red Algae is very vast and even very interesting too because of its vast nature. The morphology of red algae is very diverse and can vary from unicellular forms to complex parenchymatous and non-parenchymatous thallus forms. Some species of red algae can have double cell walls, too, which help their existence in the deep marine environment. The outer layer of red algae's cell wall contains agaropectin and polysaccharides agarose and, we can extract them both from red algae. If we want to extract polysaccharides agarose and agaropectin from the cell wall of red algae, we have to boil them as agar. The internal cell walls of the red algae are usually made up of cellulose. Other than this, red algae also have the most gene-rich plastic genomes known till now.
The Cell Structure of Red Algae:
During the entire life cycle of red algae, they do not have centrioles and flagella present in them. Following are some of the main characteristics of the red algae based on their cell structure:
These are some of the unique characteristics of the red algae species based on their cell structure and its features.
Red Algae: Evolution
The evolution of the red algae takes us back to the oldest evolutionary lineages of the photosynthetic eukaryotes, and that's why red genes of algae are considered as one of the oldest genes present on the planet. Firstly, the chloroplasts evolved, which is followed by the endosymbiotic event. The endosymbiotic event is an evolutionary event that took place between an early eukaryotic phagotrophic and an ancestral, photosynthetic cyanobacterium. This evolutionary event, which is also termed primary endosymbiosis, resulted in the origin of red as well as green algae and the glaucophytes. Glaucophytes are the organisms that mark up the oldest evolutionary lineages of current photosynthetic eukaryotes.
After the primary endosymbiosis event, the secondary endosymbiosis event takes place in which the involvement of red algae has been found. In the secondary endosymbiosis event, a heterotrophic eukaryotic and an ancestral species of red algae resulted in the evolution as well as diversification of many other photosynthetic organisms' evolutionary lineages. It is found from the evolutionary lineages that not just the multicellular brown algae species but actually half of all known species of microbial eukaryotes have plastids, derived from red algae, present in them.
Red Algae: Fossil record
Red algae, which is one of the oldest fossils identified, is also the oldest fossil from the eukaryotes, which belongs to a specific modern taxon system. One of the multicellular fossils obtained from arctic Canada, i.e., Bangiomorpha pubescens (fossil name), strongly resembles Bangia (a modern red algae species). This fossil obtained from arctic Canada has been found to occur in rocks that dated around 1.05 billion years old. Many other fossils of red algae found between 2006 and 2011 are well-preserved in the sedimentary rocks present in the Chitrakoot of central India.
Red Algae: Ecological and environmental importance
Red Algae plays a very important role in carbon sync, and they also perform the synthesis of many metabolites and fatty acids. As we have mentioned, red algae act as carbon sync; they have a very important role in the production of oxygen in the seawater. If we talk about the impact of red algae on the aquatic food webs, we will find that their role in these aquatic food webs is indispensable. Various species of red algae are a good source of food for many marines and aquatic organisms such as worms, fishes, etc. Also, with this, the biogeochemical impact of the red algae in climate change and global climate is huge and powerful.
Other than this, the commercial and economic value of red algae for humans is undeniable, and they are used as an important economic source. The red seaweeds are used as a food source for human consumption, and also, there are many industries that are based on the food processing of many red algae species such as nori. The red algae consist of high and rich mineral contents, which include carotenoids, antioxidants, vitamins, and protein, and these all make red algae a popular food choice in the health food industry.
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