In previous articles we have seen in depth the red algae. Today we bring you another article related to it. In this case we will talk about green algae. Their special characteristic is that they contain both a and b chlorophyll. This fact is what gives green algae their color. There are more than 7.000 species of green algae worldwide, although some estimates put the number above the ten thousand speciesThey are divided into marine, freshwater, and terrestrial species, although the vast majority are freshwater.
Do you want to know in depth all the characteristics and way of life of green algae? Keep reading and you'll learn everything.
Key features
Water Pollution It decreases the amount of sunlight entering marine ecosystems, and therefore green algae cannot photosynthesize and die. This type of algae can inhabit almost any ecosystem because it has a great survivabilityThe fact that only 10% of all green algae in the world are marine is related to their ability to photosynthesize and their need for sunlight.
When we go out to sea, we can find many types of green algae. As we go down in depth, we see less and less as the sunlight diminishes. Although we can find some algae suspended in the water or algae of microscopic size, the vast majority of them are at the bottom of the sea floors. In clear waters They can reach higher levels than in turbid waters.
Reproduction in algae can be both sexual and asexual.. When analyzing them, we can distinguish stems, leaves and roots just like in a higher plant. In reality, the body of the algae is a stalk, a structure without vascular tissues, but which can present very complex laminar, filamentous or macroscopic forms.
What are green algae and how are they classified?
Green algae comprise two major lineages within green plants (Viridiplantae): Chlorophyta (most of the classic green algae) and Charophyta (charophytes), the latter being closely related to land plants. Several main classes are recognized, including Prasinophyceae, Ulvophyceae, Trebouxiophyceae, Chlorophyceae y Charophyceae. Some works distinguish additional prasinophyte clades (e.g., Pyramimonadales), and in regional catalogues, closely related groups may be listed; however, the most widely accepted classification integrates the above classes within Chlorophyta and Charophyta.
The group is very large: there are species unicellular, multicellular y coenocytic (a large cell without partitions, with one or more nuclei). Many green algae are euryhaline, capable of tolerating large variations in salinity, which is why they thrive in transition zones such as estuaries and rivers, and also in ponds, lakes, wet soils or forming films on bark and walls.
Pigments, physiology and cellular traits
Its color is due to the presence of chlorophyll a and b in a similar proportion to terrestrial plants. They also possess carotenoids (α and β-carotene) and xanthophylls (lutein, siphonoxanthin) that protect against radiation. Under high sunlight conditions, whitish tones can be seen due to optical changes, and some terrestrial species accumulate so many carotenoids that they acquire reddish or orange tones to protect against excessive light.
As a reserve substance, accumulate intraplastidial starch, usually around the pyrenoids within the chloroplast. The chloroplast is surrounded by two membranes and their thylakoids are grouped in grana. In numerous genera there is eyespot (stigma) light-sensitive, key to the orientation of mobile forms.
Cell walls are usually made of cellulose and may be covered by mucilage; in some groups they appear calcareous depositsFlagellated cells exhibit apical or lateral flagella depending on the class. At the level of cell division, they present both open or closed mitosis and cytokinesis may involve cell plate (phycoplast) or be done by intussusception, useful features in group systematics.
Morphological diversity and representative examples
The diversity of forms is enormous: Chlamydomonas (flagellated unicellular), Chlorella (coccoid), Pediastrum (colonies), Klebsormidium (single filaments), Cladophora (branched filaments), Udotea (siphonal), Codium (pseudoparenchymal) or Coleochaete (parenchyma). Many macroscopic marine species of Ulvophyceae (for example, Ulva) form cosmopolitan distribution sheets.
There are perennial species, such as Codium tomentosum, and other seasonal ones that, under conditions of light and nutrients, experience explosive growth generating “green tides”These proliferations are natural, but are exacerbated by excessive nutrient intake.
Habitat, distribution and ecological importance
Most green algae live in continental environments (fresh water, wet soils, rocky surfaces). Prasinophyceae and especially Ulvophyceae are more frequent in marine or brackish watersMany are cosmopolitan and adapt to variable environments where few species thrive.
In the sea, they are present wherever enough light arrives. Most are Bentonicos (linked to the bottom), although there are planktonic representatives that are part of the phytoplankton. Ecologically they are essential: they maintain food webs, produce oxygen and contain species that establish symbiogenesis with fungi to form lichens or with aquatic invertebrates such as sponges and cnidarians.
Reproduction of green algae
As we mentioned before, algae can reproduce asexually by fragmentation and sexually in various ways. Let's analyze each of them, incorporating the most common variants:
- Hologamy: it is a type of reproduction that is only observed in unicellular algae. Its reproduction consists in the fact that the whole alga itself acts as a gamete and fuses with another gamete.
- Conjugation: This is a type of reproduction that only occurs in algae that are filamentous (for example, Spirogyra). In it, some algae act as males and others as females. In this way, they are able to join the filaments and create connecting tubes through which the reproductive content passes. When the process is complete, the result is a zygospore. It is a spore that remains dormant until the environmental conditions are suitable for its germination, in which it forms a new filament. It can be isogamous or anisogamous depending on the relative size of the nuclei involved.
- Planogamy: reproduction by motile gametes; both males and females have flagella and can move to find each other. It can be isogamous if the gametes are similar or anisogamous if they differ.
- Oogamy: In this case the female gamete is still since they lack a flagellum. Fertilization can be external (releasing the gamete) or internal if it remains within the gametangium that produces it.
In addition, many chlorophytes multiply vegetatively by cellular division and by asexual spores (flagellated zoospores or aplanospores), very effective mechanisms under favorable conditions.
Biological cycles and alternation of generations
Life cycles range from simple schemes to complex alternations:
- Monogenetic haplophasic or diplophasic: with a single generation, the dominant nuclear phase can be haploid or diploid. Codium tomentosum It presents a diplophasic cycle.
- Haplodiplophasic digenetic: alternation of generations isomorphic or heteromorphic (sporophyte and gametophyte similar or different). Isomorphic examples: ulva lactuca, Ulva intestinalis o Cladophora rupestris.
During these alternations meiosis occurs zygotic, sporangial o gametangial according to lineage. These traits are used to taxonomic diagnosis and help explain the ecological plasticity of the group.
Filamentous algae
Filamentous algae are of public interest, as many of them are used in aquariums. They have both chlorophyll a and b and various types of pigments such as carotenes and xanthophylls. We find them mainly in freshwater areas, although they can also be seen in marine environments. This makes them a versatile plant to use in your aquarium.
They are called filamentous algae because they have cells shaped like filaments like compact hairs. In some aquariums, a type of filamentous green algae (similar to weeds in gardens) that is not very pleasant forms. CladophoraYou can easily recognize them because they look like a group of dark green filaments and grow attached to substrates or other surrounding plants.
Filamentous algae need a lot of light and nutrients to grow well.They require large amounts of nitrates and phosphates found in the water. If you want to ensure the healthy growth of green algae in your aquarium, make sure they have a good supply of these minerals.
These algae can also become a pest if there is excess nutrients. They can damage the waters through a process known as eutrophicationThis is an exaggerated growth caused by excess nutrients in the water, which leads to a reduction in the amount of light reaching the bottom due to the excess algae. When they die, they begin to rot, creating a putrid environment.
Causes why they appear in your aquarium
You may have a pond that suddenly starts to grow green algae. This situation can be caused by a variety of reasons. One of the main ones is the imbalance between nitrate and phosphate in the water. There are usually more nitrates than phosphates. Inadequate levels cause these algae to grow in aquariums. To avoid this situation, we must carefully control the levels of plants we place in the pond.
Another problem that triggers unwanted growth of green algae is the low filtration or biological loadThis situation occurs when The filters they do not have the necessary power to keep the water in good condition. It may be because the aquarium does not have enough power to filter a large amount of water or too large a volume or because it has become blocked / damaged. To take this aspect into account, we just have to look for the necessary power at which it has to work. It should be noted that when inserting the filter into the water, power is reduced by 40%. Therefore, it is necessary to purchase a filter with greater power.
If the aquarium has a excessive direct sunlight or, on the contrary, a lack of lighting, unwanted growth may occur. The amount of light entering must be well-measured and just right.
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Prevention and control in aquariums: nutrient and light balance
To keep unwanted green algae at bay, provide a balanced N:P ratio (guidelines between 10:1 and 20:1 in mg/L), with periodic nitrate and phosphate tests. Fast-growing aquatic plants help to consume excess nutrients. Avoid overfeeding de peces and siphons the bottom to remove debris, sources of ammonium and phosphate.
Set the photoperiod to 8–10 hours daily with lighting appropriate to the volume. Direct natural light tends to trigger proliferation; if you can't avoid it, use curtains or relocate the urn. Keep the filters with mature biological media and sufficient flow (consider the decrease in performance under water) and complement with regular water changes of the 20-30%.
The introduction of algae consumers (e.g., snails and some species of shrimp or fish, depending on compatibility) can help, but never replaces correcting the root cause: light, nutrients, and filtration.
Economic importance and uses: biostimulants and more
In addition to their ecological value, several green algae are sources of bioactive compounds and are used as biostimulants non-microbial agricultural products. Their extracts improve nutrient absorption, fertilizer use efficiency, and water tolerance. abiotic stress (drought, salinity, oxidation), with benefits for sustainable agriculture.
- chlorella vulgaris: a single-celled microalgae with a high protein, vitamin, and mineral content. Its extracts provide phytohormones and amino acids, increase soil microbial activity and help resist drought and salinity.
- Dunaliella saline: halophilic that accumulates beta carotene, a powerful antioxidant. It improves photosynthetic efficiency and protects against oxidative stress.
- ulva lactuca (sea lettuce): macroalgae rich in polysaccharides and minerals. Its compounds act as soil conditioners, promote root development and nutrient absorption.
- scenedesmus spp.: versatile microalgae with high content of lipids and proteins, useful for stimulating performance and stress tolerance.
- Spirogyra spp.: filamentous freshwater, rich in amino acids and antioxidants, which can promote root growth and soil microbial activity.
These uses are added to applications in aquaculture (as food or water enhancement), in biotechnology (production of pigments and metabolites) and, in certain cases, in bioremediation to capture nutrients in effluents.
“Green tides” and eutrophication
When the load of nitrogen and phosphorus It is triggered by urban, agricultural or livestock contributions, certain green algae proliferate massively, decreasing the transparency of water and, when it dies, its decomposition consumes dissolved oxygen, being able to generate anoxic environments. This process, the eutrophication, affects rivers, lakes and coastal areas. Addressing it requires reducing nutrients at source, restoring wetlands and improve the treatment plants.
Comparison with terrestrial plants and evolutionary relationship
Green algae share with terrestrial plants chlorophyll a and b, starch as a reserve and walls rich in cellulose. In Charophyceae we find cellular features (for example, phragmoplast in cytokinesis and thickened-walled zygotes, the zygospores) that suggest the evolutionary transition to plants vascular. This link explains their importance in understanding the origin of terrestrial flora.
I hope these tips help you learn more about green algae. Knowing their diversity, physiology and cycles allows us to appreciate them as pillars of aquatic ecosystems and, at the same time, as allies in aquariums and agricultureBy properly managing light and nutrients, and appreciating their ecological and biotechnological role, it is possible to live with them in a healthy and beneficial way.