What does Volvox algae eat

Information on algae in the aquarium, in the garden pond and in nature

Green algae between crab claws.

Bearded algae on an Echinodorus leaf.

Algae can form in any small accumulation of water within a short period of time. In a garden pond, in an aquarium, in a rain barrel, even in a glass of water on the windowsill or in the nipple trough of the rabbit hutch. Algae are adaptable and multiply quickly under favorable conditions.
In the aquarium or pond, algae are annoying and can become a real nuisance. Green algae mainly occur in the garden pond. It is either thread algae that float in thick mats on the water or hang between the plants, or floating algae that cloud the view of the fish as "green water". In nature, these algae are an important source of food for small creatures such as water fleas and hippos, which in turn serve as food for fry. Mussels also use floating algae as food. However, if there is a mass increase in algae, there is a risk that the pond will "tip over."
In addition to green algae, blue algae, diatoms and the particularly unattractive beard algae or brush algae occur in the aquarium.
Here you can find out what kind of algae they are and how you can fight them successfully.

On the biology of algae

Algae are not a uniform systematic group with a common history of ancestry. For example, green algae, together with land plants, belong to the group of chloroplastida. This is a group of living things with real cell nuclei that carry out photosynthesis. However, algae are also used to describe organisms that belong to bacteria (blue-green algae = cyanobacteria) and life forms that are close to fake fungi (e.g. downy mildew).
The life requirements of these organisms are very different. That is why not all algae in the aquarium or in the garden pond can be combated with the same agent. In order to act effectively against an undesirable algae plague, it is helpful to know which group the algae belong to and then, if possible, by changing the environmental conditions, deprive them of their livelihood and improve that of other organisms (competitors, algae eaters) in the habitat.
The Blue-green algae (Cyanophyta) are bacteria-like organisms without a real cell nucleus. They can make chlorophyll a. Their cell walls consist of murein and lipopolysaccharides.
Brown algae, diatoms and dinoflagellates belong to the ancestry group of stramenopiles, alveolates and rhizaria (SAR). They form the chlorophylls a and c. They use laminarin, mannitol and oil as storage materials. Their cell walls contain silica, alginates and mucopolysaccharides. The egg mushrooms or false mushrooms (Oomycetes) belong to their family group. They are decomposers or parasites on plants and animals. The oomycetes include the downy mildew fungi, the causative agent of crayfish plague (Aphanomyces astaci) and late blight on potatoes and late blight on tomatoes Phytophthora infestans.
Green algae and Red algae are similar to higher plants in their metabolism. This means that they have similar needs as our aquarium plants and the water plants in the garden pond. They have a cell metabolism in which they breathe sugar into water and carbon dioxide. To cover their energy needs, they are able to synthesize sugar from carbon dioxide and water with the help of chlorophyll a and chlorophyll b. They use starch as a storage substance and their cell walls are composed like those of higher plants. There are unicellular algae, colony-forming species and multicellular algae. Unicellular species the green algae live z. B. as plankton in free water, colonize damp earth and even grow on snow. In the sea they sometimes live in the body of other animals and provide them with nutrients (some jellyfish, mussels and snails). You can make lichen with mushrooms.
Colony-forming species are single-cell organisms that adhere to one another but have separate metabolisms. These include, for example, the species of the genus Dinobryon.
Provide a transition form between the colony-forming unicellular organisms and the multicellular organisms Colonial individuals represent. The green alga Volvox consists of thousands of cells connected by plasma bridges. Certain areas of the resulting spherical complex are specialized in reproduction, others are only part of the structure. Bryopsis has a feather-like structure. The individual threads each consist of a multinucleated cell. This arises from the fact that no partition walls are formed during cell division.
Multicellular algaethat form differentiated tissues are called tange. The sea salad (Ulva spec.) is a green alga and a seaweed. It adheres to the ground with specialized root cells. Some red algae (e.g. Palmaria sp.) are Tange.

The reproduction of the algae is very different. Algae multiply by division and sexually. Some form permanent forms - cysts - that withstand drought. This allows them to rest in the ground until water collects in a depression after a rain and then continues to multiply. During sexual reproduction, flagellated spermatocides or amoeboid forms can develop. The adult forms can also be flagellated in some species and actively move around.

Cyanophyta - blue-green algae, cyanobacteria

In addition to cyanobacteria, other organisms can also be found in the blue-green algae mats. Here grows between the thin blue-green threads of Oscillatoria a green thread algae. Nematodes and rotifers look for food among the algae.

Cyanobacteria on waterweed.

Cyanobacteria mainly settle in places where food remains.

Blue-green algae were the first single-cell organisms to begin photosynthesis 2.5 to 3.4 million years ago. They are relatively undemanding and adaptable. There are unicellular, colony-forming and multicellular species (chain formation). Their cell walls are thick and gelatinous, so blue-green algae form greasy layers. Some species are able to bind nitrogen from the air. These species live e.g. in symbiosis with algae fern (Anabaena azollae in Azolla sp.). These plants are therefore used specifically to increase the nutrient content in the water of rice fields. Around 4000 different types of blue-green algae are known. In the aquarium mainly occur Oscillatoria-Types on.
Blue-green algae do not have a nucleus in which the DNA of higher forms of life is concentrated. Their genetic material is exposed in a part of the inside of the cell called the centroplasma. This area of ​​the inside of the cell is colorless or difficult to stain. Around it lies the chromatoplasm that contains the colorants important for photosynthesis. Blue-green algae can be blue-green, blue, blue-black or yellow-brown. Characteristic is the occurrence of the pigment phycocyan, which occurs in addition to chlorophyll a, phykoerythrin, carotenes and xanthophylls. Blue-green algae reproduce exclusively asexually by dividing. They also do not develop flagellated forms.

Problems with blue-green algae in the aquarium

Blue-green algae are one of the most common algae in the aquarium. The blue to black algae coatings are unsightly and can take the light out of plants in the aquarium, causing them to perish.
More problematic, however, is that cyanobacteria produce toxins that harm the animals in the aquarium. Blue-green algae are unpopular as a source of food for the animals in the aquarium. There are therefore no cleaning collones that completely eradicate the blue-green algae.
Various scientific studies have been carried out on the relationship between mud snails and cyanobacteria. Radix auricularia can the poisonous cyanobacteria Microcystis farlowania and Pseudanabaena franquetii eat without being damaged. Lymnaea stagnalis eats the cyanobacterium Planktothrix agardhii and so takes the poisonous Microsystine on. The animals are not selective when eating. Even if they are offered other food (salad), they will still eat the cyanobacteria. The snails are not harmed by this because only a small amount of the poison gets into their metabolism. 95% of the toxin remains in the digestive tract of the animals and only a little gets into the rest of the body (Lance et al. 2005). Most of the toxin can then be excreted with the faeces. After about 6 days, 80 to 95% of the poison has left the snail's body (Zurawell et al. 2006).
However, if the blue-green algae disintegrate in the water, the microcystin in the aquarium water is released and can kill the snails. Mycrocystin from cyanobacteria can be detected in the water for about 3 weeks after an algae bloom and the disintegration of the algae. Under normal circumstances, concentrations of up to 140 µg / l have been measured. After treatment with algicides, the concentration can increase to 1300 - 1800 µg / l. That is why snails and possibly other invertebrates die as a result of algae control measures, even if the agent itself is harmless to them.
But even a permanently low concentration of blue-green algae toxins can be dangerous for the animals. If they are constantly exposed to the poison, it accumulates in the tissue of snails and damages them. At Lymnaea stagnalis 33 µg of microsystin per liter in the water is sufficient to reduce the number of eggs produced by half (Gérard et al. 2005). Blue-green algae in the aquarium can therefore reduce the fertility of invertebrates.

Fight against blue-green algae in the aquarium

Blue-green algae in the aquarium are not only unsightly, but also dangerous for the animals in the tank because of the toxins that are formed. That is why they must not be found in large quantities in the aquarium. Reasons for an increased occurrence are over-fertilization (phosphate, protein residues), poor ventilation of the soil and a lack of oxygen. Eliminating the causes is the only effective control method in the long term:
- Removal of leftover feed and rotting material
- cleaning the filter
- possibly additional ventilation
- less feeding.

The use of apple snails, racing snails, mud snails or ramshorn snails counteracts blue-green algae. They reduce the organic waste that is colonized by the algae and also eat small amounts of the algae. Because of the blue-green algae toxins (see above), large amounts of cyanobacteria damage them. It is therefore not to be expected that they will simply eat up large blue-green algae mats.

A "dark cure" is most effective against cyanobacteria. Schwermer (1990) and Kaufmann (2010) recommend darkening the aquarium completely for five to seven days. Not only is the aquarium lighting switched off for darkening, but the panes are also covered with cardboard. If available, a CO2- Fertilization must be turned off.
Due to the deprivation of light, the algae die and dissolve. This releases toxins into the aquarium water.
That is why it is very important to do a big water change before the dark cure, during which as much as possible of the blue-green algae is sucked off. Even in the days after darkening, when the algae have died, large water changes must be carried out several times. This removes the nutrients and toxins released from the dead blue-green algae from the aquarium.

Bactericidal agents can also lead to the death of blue-green algae. Fish medicines as well as sea almond leaves or alder suppositories can be effective against blue-green algae.
There are reports that adding potassium sulfate or potassium chloride caused blue-green algae to disappear from the aquarium (Vrabec 1989, Kluczniok 1989). In these cases, the administration of potassium probably had a positive effect on the growth of the aquatic plants, which made them more competitive. Other authors report that this treatment was unsuccessful for them (Greger 1990).

Vegetable algae

Green algae, chandelier algae and red algae belong to the realm of plants. They have a nucleus and brown, brown-green, green, red or yellow chromatophores.
The green algae belong to the Phyllum Chlorophyta, the red algae to the Phyllum Rhodophyta and the chandelier algae are assigned to the Phyllum Charophyta.
There are sedentary and free-living species. Many species of algae have flagellated, actively moving stages.

Green algae = Chlorophyta

green water in an aquarium

Floating algae from a water sample from the aquarium under the microscope: Hyaloraphidium contortum, Scenedesmus acuminatus and Monorhaphidium contortum

green spot algae - Coleochaeta spec.

bristly, hard thread algae

slimy thread algae


So far, over 7,000 species of green algae have been described. 90% live in fresh water. There are only a few marine species. Ulva and Enteromorpha form leaf-like structures. Enteromorpha becomes up to 30 cm long and sits firmly on stones, shells or wood. It occurs in coastal waters and estuaries around the world where herbivores are absent.
Most green algae are unicellular and part of the plankton (z. B. Chlamydomonas and Chlorella). These planktonic green algae are the basis of the food network in fresh water. Small crabs, fry and mussels feed on them. The unicellular green alga Chlorella vulgaris is used as an additive for fish feed and as dust feed for young fish or filter feeders.

Green water from floating algae

"Green water"is caused in freshly set up aquariums and ponds by a mass multiplication of floating algae. These are green algae of the genera Acinastrum, Ankistrodesm, Ocystis, Pandorina, Pediastrum, Scenedesmus and Volvox. Sphaerella, which is often brought into the aquarium with rainwater, gives the water a brownish color. Diatoms and cyanobacteria can also contribute to cloudiness.

The "green water" initially only obstructs the view of the fish, but it can also be dangerous for the animals
The algae produce a lot of oxygen, which is initially positive for the animals. However, if the oxygen content rises above the saturation of the water, gas bubble disease can occur in the fish. Gas bubbles form in the blood vessels of the fish and can trigger amboli. Blisters can also form in the skin and fins. In water that is oversaturated with gases, the animals are also more susceptible to infectious diseases (gas bubble disease at Wikipedia).
It becomes even more problematic when the algae die. Then suddenly large amounts of nutrients (phosphate, nitrate) are released from their cells, which stimulate a new algal bloom. When the organic matter is broken down by bacteria, there can also be a massive lack of oxygen and the formation of toxic fermentation gases. For this reason, it is not advisable to simply kill the floating algae in the green water with chemical agents.

Combating floating algae

Flocculants are commercially available to combat floating algae. They contain metal salts such as iron (III) chloride or aluminum salts. They clump together with suspended matter (algae, humic substances) and form flakes that sink to the bottom. The algae must not rot there, but must be vacuumed off. This is less of a problem in an aquarium than in a garden pond.
The flocculants can only be used in well-buffered water (KH above 5), otherwise they will greatly reduce the pH value. A drop in pH can cause acid burns on the fish's gills, which can lead to death. Flocculants are therefore unsuitable for use in ponds that are only fed by rainwater or filled with soft tap water.

The algae can also be flocculated with the help of a UV-C lamp. The heater is inside a tube and is connected to the water inlet before the filter. In some pond filters, a UV lamp for combating algae and germs is already integrated. In aquariums, they can be connected upstream of external filters.
The water flows through the tube past a lamp that emits UV-C radiation. The radiation kills or damages the algae cells and causes them to clump together. The dead algae remain in the filter or collect on the bottom. The residues have to be vacuumed off so that they do not rot and release nutrients from them that would encourage new algal blooms.

Thread algae

The thread algae are multicellular green algae. This includes species from the genera Mougeotia, Zynema, Pithophora, Oedogonium, as Cladophora, Aegagrophila and Spirogyra-Species. There are always some thread algae to be found in the aquarium and pond. If the nutrient supply is relatively low, thread algae are no longer noticeable. They produce oxygen and serve as food for some animals. Shrimps and crabs in particular like to eat green algae. Effective algae control with the animals only works if they are not offered energy-rich flake or granulated food that is excessively more easily accessible. Then the shrimps fertilize the water with their excretions and have less appetite for algae.
In the case of mass reproduction, thread algae wrap themselves up and take away their light. Fine feathered aquarium plants (e.g. Cabomba aquatica, Limnophila aquatica) can quickly die off as a result. In the pond, Dadenlagen often swim as dense mats on the water surface and are carried by oxygen bubbles.

Fight thread algae in the aquarium and pond

Thread algae can be removed by hand. In the aquarium, the threads can be wound on wooden skewers. For the pond, bottle brushes are suitable for winding up or landing nets for fishing off the mats. Without further measures, however, the algae grow back quickly.
The reason for the abundant growth of thread algae is an excess of nutrients in the water. In the aquarium, this can best be reduced with regular water changes.
In the pond, more pond plants should be used to reduce the nutrients. Fast-growing plants are particularly suitable. Waterweed and hornwort absorb a lot of nutrients quite quickly. In doing so, they grew strongly. By removing excess plants from the pond, the excess nutrients are also removed from the biotope.
In the long term, the cultivation of other underwater plants such as Vallisneria, spawning herbs and milfoil is also recommended in the pond. Reeds and cattails are used in organic sewage treatment plants to effectively reduce nutrients. However, their roots can break through pond liner and are also more difficult to remove than other pond plants.

It should be possible to combat green algae in the aquarium with aspirin. Brush algae and thread algae are said to die if you add one tablet of aspirin per 1000 l to the water (Eggers 1989). According to Rainer Münch's observations in Strobeck, the snails eat larger amounts of the algae after adding aspirin to the water.
The use of algicides is not advisable either in the pond or in the aquarium. Thread algae are close to the higher plants and are only killed by herbicides that also damage the plants. Copper preparations are also unsuitable because at concentrations of 0.03 mg / l they not only kill the algae, but also the filter bacteria. From 0.08 mg / l copper damages higher plants (waterweed, Vallisneria) and is also poisonous for crustaceans (shrimp, crabs, water fleas) and insect larvae (dragonfly larvae). Higher concentrations from 0.1 mg / l are poisonous for fish. An exact dosage may still be possible in the aquarium. However, the volume of a pond cannot be determined precisely enough for such a treatment. The Kupfger remains in the pond even after the treatment. it is tied to the bottom in the mud. With each new treatment, the burden on the ecosystem increases.

Thread algae for decoration

Incidentally, thread algae also include the popular moss ball (Aegagropila sauteri). However, it does not belong to the genus Cladophora, like the thread alga pictured above on the right. While at Cladophora If there are individual, highly branched single threads, the threads become matted Aegagropila. There are also significant differences in the composition of the cell walls that are used in Aegagropila also contain chitin, as well as the chloroplases, which differ in their carotene composition.

The water network - a special green alga

The water network (Hydrodictyon reticulatum) is a particularly filigree and interesting alga. This alga belongs to the Hydrodictyaceae. It occurs in lakes, ponds and rivers. It forms colonies from many thousands of cells that are arranged in a sack-shaped network. As a rule, three tubular cells about 1 cm long meet at each node of this network. In this way, honeycomb-shaped, four, hexagonal or octagonal meshes are formed. Every cell has numerous nuclei. During reproduction, up to 20,000 flagellated zoospores develop within the cells, which are already arranged in a network in the mother cell. By tearing the membrane of the mother cell, the net is released and grows quickly. The wet algae floats freely in the water and can be about 20 cm long. It occurs in clean to moderately polluted waters.

A network of Hydrodictyon reticulatum and the cells of Hydrodictyon reticulatum

Brush algae, beard or red algae = Rhodophyta

Bearded algae are filamentous red algae of the genus Compsopogon

Tricleocarpa cylindrica is widespread in tropical seas.

Brush algae in a freshwater aquarium are nowhere near as attractive.

Thorea ramosissima in an aquarium

There are around 4,000 species of red algae. They are red to black and mostly adapted to tropical climates. Some species colonize fresh water or moist soil. However, they mainly occur in the sea.
Many red algae species are Tange and are not adapted to great depths up to 260 (e.g. Caloglossa leprieurii). Other species have more filigree, thread-like structures. Corallina spec. almost look like corals because they store calcium carbonate in their cell walls.
No red algae occur in garden ponds. But the bearded algae and brush algae in our warm water aquariums are tropical red algae. The Bearded algae are red algae from the genus Compsopogon. They form flat lawns from long gray-green to blackish, branching threads.
At Brush algae the threads grow from circular bearings. These algae belong to the genus Audouinella.
Red algae cannot be removed from plant leaves, as they tend to adhere firmly to them. If the infestation is severe, the plants die.

Fight beard algae and brush algae in the aquarium

Beard and brush algae thrive particularly well in hard, poorly filtered water. In alkaline water (pH value> 7) they indicate a carbon dioxide deficiency. High phosphate levels promote the growth of brush algae and beard algae.
To combat it, the leaves and decorative objects that are initially infected are removed. They are scraped off the filter and heater with a scraper.
Repeated water changes remove the excess nutrients from the water. Afterwards, phosphate is repeatedly released from the substrate. That is why the water changes must be repeated every 2 days until nutrients no longer dissolve from the substrate and the nutrient load in the water really decreases.
At the same time, rapidly growing aquarium plants are placed in the aquarium. Waterweed, Vallisneria, Ludwigia and Indian water friend are particularly suitable. These plants grow quickly and their leaves are quite short-lived, so the red algae cannot develop well on them. Slow-growing species such as anubias or ferns, on the other hand, are heavily colonized by beard algae and brush algae, because the leaves become several months old and the algae therefore have plenty of time to develop.
In order to promote the growth of the aquarium plants, missing nutrients must be added as fertilizer. In most cases, these are potassium and microtubes (iron, molybdenum, etc.). However, this can also include fertilization with nitrogen. If only the phosphate load is high, but no nitrate can be detected, the aquarium plants cannot grow properly and the red algae have an advantage. Fertilization with a nitrogenous fertilizer then improves plant growth and the aquarium plants become more competitive for the algae. Also a CO2-Ferting can improve plant growth when the pH is high in hard water.

Animals cannot be used to successfully combat red algae. Nibble fish (Garra spec.), Amano shrimp and ramshorn snails probably eat brush algae if they have no other choice. Other algae eaters do not take the algae. Armor catfish are constantly scraping (and often damaging) the leaves of Anubias and other plants, but they are not effective at getting rid of the algae.

A special red alga

The freshwater red alga Thorea ramosissima Bory occurs in European rivers. It belongs to the Thoreaceae family. The thalli grow upright. They are round, flexible and soft in cross-section. They are branched and their surface is covered with threads of assimilation. They feel slimy. Multiplication takes place via monospores. Thorea ramosissima is the most common type of 5 or 6 in the genus. It grows on solid substrates and becomes about 10 to 15 cm high or long there.
The photo (bottom right) was taken in the Botanical Garden in Munich. There the alga has been growing in an aquarium with hard, alkaline water since 2004. For technical reasons, there is no carbon dioxide fertilization in the aquarium (Bogner 2004). Apparently, the algae find optimal conditions in this way.

Candelabra = Charophyceae

Growing in the background Chara in the aquarium.

Chandelier algae lawn (Nitella) under a stock Potamogeton

Thallus of a candelabrum from the genus Nitella

Nitella at the bottom of a body of water

Candelabra (Nitella sp.) with male gametangia between Vallisneria nana and Egeria densa

Chandelier algae belong to plants like green algae. In Rothmaler (1994) seven species are described for Germany.
The thallus of candelabrum resembles the stem of a horsetail. The shoot has long internodes and short nodal cells. There are lively branches at the nodes. The first-order branches are called radii, rays, "leaves" or short shoots.
The radii themselves are also divided into internodes and nodal cells. The second order branches are radioles or "leaflets".
At the base, the thallus adheres to the substrate with rhizoids.

There are different genera of candelabrum algae, which are differentiated on the basis of degree of branching, presence or absence of a stipular wreath and characteristics of the oogonia (female gametangia). With the genera Chara and Charopsis are z. B. wreaths of bristle-shaped cells below the radii. At Nitella the radii are forked.

The chandelier algae multiply through the fusion of gynogametangium and androgametangium. This creates the oosporangium, which corresponds to a fruit. It consists of an oospore and a bowl. At Nitella and Tolypella the oogonium is ten-cell. For the other genera (Chara, Nitellopsis, Charopsis etc.) it is only five-cell.

Chandelier algae are often covered with calcium carbonate and are therefore also known as calcareous algae.
These plants can be found in nature on the bottom of the water. They grow flat on the ground alone or between aquatic plants.

Chandelier algae as aquarium plants

Chandelier algae do not appear as "harmful algae" in the aquarium. The care of some Chara-Species as a substitute for horn leaf or Najas is possible. A Nitella- A species that is seldom available in stores has a fine, green thallus. It is about 1 mm thick. There are 6 or 7 radii at each node. The lower radii are simply forked. The upper ones are not bifurcated or begin to divide at the tip. The internodes are about 1 to 2 cm long, the radii between 0.5 and 1.5 cm. The plants are not difficult to care for: temperature: 22-26 ° C, pH value: 6.5-7.2, hardness: 8-20 ° KH, light: little to much.

Nitella is only branched once. Chara is heavily twisted.

Stramenopiles, Alveolates and Rhizaria (SAR)

Hormophysa cuneiformis is a common species.

Hormophysa cuneiformis in a rock pool at Cape Tribulation (Queensland, Australia). The plant becomes about 40 cm high.

The Padina-Species form conspicuous shapes. The thalli are calcified.

Larger specimens curl or form funnels.

Brown algae (Phaophyceae), golden green algae (Xanthophyceae), golden brown algae (Chrysophyceae), the diatoms (Bacillariophyceae) and the Oomycophyceae belong to the realm of the Chromista and are not plants. Their relatives include, for example, downy mildew and late blight and brown rot. These are species that have a developmental stage with heterocontaneous flagellation. They have a long pulling flagellum and a shorter dragging flagellum. The pulling flag is directed forward.

Brown algae = Phaeophyceae

Brown algae are found almost exclusively in the sea and predominantly prefer cold water there. There are around 1,500 species. The algae contain chlorophyll, but other pigments (e.g. fucoxanthin) are superimposed on it. They are adapted to deeper sea regions through a special photo system. They are multicellular and clearly divided into organs, stems and leaves. Brown algae include seaweed (e.g. Dictyota dichotoma and Postelsia spec.). The giant kelp (genus Macrocystis) grows to a height of 80 m. In cold polar coastal waters it forms dense forests.

Some SargassumSpecies do not adhere to the ground, but float freely in the open sea by means of gas bubbles. They create a floating habitat for crabs, shrimp and young fish.
Brown algae are almost impossible to keep in saltwater aquariums, as they become very large on the one hand and secrete large amounts of organic slime on the other, which enables the rejection of calcium carbonate, which the plants produce during photosynthesis (biogenic decalcification).
The brownish algae in freshwater or reef aquariums are mostly diatoms.

This tang (Ecklonia radiata) was washed up on the beach at Coffs Harbor, NSW, Australia.

Golden brown algae = Chrysophyceae

Approx. 850 species. They are part of the freshwater plankton. Most species form colonies. They can appear as floating algae in the aquarium.
Some clans also grow on other algae, e.g. B. on thread algae or on moss leaves. They rarely appear alone in crowds. As part of the green water, they are combated as described for the green algae.

Diatoms on thread algae

Diatoms on thread algae

Diatoms, diatoms = Diatomophyceae

There are around 10,000 species. They are colored yellow or brown. Hydrated silicate is embedded in their cell walls, so they are relatively heavy and their outer shape is rigid and inflexible.
Diatoms are part of the plankton. They contain chlorophyll and are the main organisms that photosynthesize in the open sea. In order to be able to swim despite their hard, heavy shell and to stay close to the light, they store fats.
In the aquarium, diatoms usually form thin, brown deposits on the panes and the decoration. They often occur when there is a lack of light. Oxygen deficiency and over-fertilization (nitrogen and phosphate) favor them. Changing the fluorescent tubes can help if the cause is not a water surface overgrown with floating plants. The promotion of plant growth reduces the nutrient content in the water and increases the oxygen content through assimilation. Diatoms are then pushed back.
The pictures on the right and left show diatoms from the Achnanthaceae family (order Achnanthales) on filamentous green algae.

The following photographs were taken with a scanning electron microscope. They are all from Joanne Green of Mullum Creek Native Nursery in Mullumbimby, New South Wales, Australia. The algae all come from a salt marsh.

Left: Amphora coffeaeformis. right: Amphora eunotia
The genus amphora is very species-rich. There are species in fresh, brackish and salt water.

Left: Diploneis sp. right: Navicula. The genus Navicula is very species-rich. They are found in fresh, brackish and salt water.

Left: Nitzschia sp. right: Rhopalodia sp.

left: detailed view of Trachyneis adspersa This species is also found in the North and Baltic Seas. right: half of a diatom bowl with a view of the inside

The snail's droppings Salanitor solida
Achnatessp. in the snail's feces Salanitor solida

Snails that graze substrates pick up pebbles. It is not entirely clear whether the algae will be damaged in the process. Only mermaid snails (Neritidae) are known to break down the algae before swallowing them. Some snails have a strong gizzard in which they absorb grains of sand and use it to grind their food. Most snails, however, do not digest diatoms very effectively and most of them are excreted undamaged. The two pictures below show the faeces of Salanitor solida. It includes whole diatoms and also fragments. It is not known whether the fragments are already being picked up in this form by the screw or whether the screw is able to crush the hard shells.

Benefits of algae

For aesthetic reasons, we find algae in the aquarium or pond to be a nuisance. But biologically they are indispensable. They produce a large part of the oxygen that is in our atmosphere today. They bind nutrients from the water and bring them into the food chain. Unicellular algae, as phytoplankton, serve as food for even the smallest larvae. Sitting algae are grazed by aquatic animals. Macroalgae are the basis of life for snails, crabs, sea urchins, fish and turtles.Even lichens, which are symbionts of algae and fungi, are used as food by reindeer, for example.
Humans also use different algae for their diet. Some algae are eaten as a vegetable (e.g. in sushi), others provide raw materials for binding agents (agar) or serve as food supplements. Fish feed contains various algae as additives. Mainly found here Chlorella (Green algae) and Spirulina (Blue algae) use.
Typical composition of Chlorella vulgaris and Spirulina platensis, S. abbreviata and S. jenneri (Source: www.drak.de, excerpt)

Chlorella vulgarisSpirulina spec.
Generally [%]

Crude fiber
Protein [%]

Amino acids, essential

Amino acids, not essential


Phosphorilated cyclitols-
Glucosamine + muramic acid-
Colorants [mg / kg]

Total carotenoids1.2003.350
of which b-carotene
k. A.
1.200 - 1.800
12.000 - 15.000
Vitamins [mg / kg]

Vitamin A600,0
Ascorbic acid (C)220,0
Biotin (H)1,90,4
Cyanocobalamin (B.12)0,100,11
Ca pantothenate13,011
Folic acid0,270,5
Pyridoxine (B.6)5,06,0
Riboflavin (B.2)6,040
Thiamine (B.1)4,055
Tocopherol (E)66,010 - 60
Ubiquinone (Q10)-
p-aminobenzoic acid (PABA)0,6-

Minerals / trace elements [mg / kg]

Calcium (Ca)4.8103.200
Phosphorus (P)9.7706.800
Iron (Fe)1.004360
Sodium (Na)16.9203.310
Chloride (Cl)
k. A.
Magnesium (Mg)3.0174350
Manganese (Mn)23,348
Molybdenum (Mo)
< 0,5k. A.
Zinc (Zn)16,750
Tin (Sn)
< 0,2k. A.
Potassium (K)16.4001.530
Selenium (Se)< 2,00,5
Lithium (Li)0,10,35
Chromium (Cr)3,03,2
Copper (Cu)2,63,0
Cobalt (Co)
< 0,5k. A.
Iodine (I)< 5,012,6
Strontium (Sr)
k. A.

In addition, dried algae serve as fertilizer or fuel. Algae are also used in the cosmetics industry.

Literature: J. Clasen (1976): Basic information on algae in freshwater aquariums - Aqua Planta 1-76, 7-8

J. Clasen (1976): The Black Brush Alga - Aqua Planta 2-76, 5-6

J. Kluczniok (1989): Experience with blue-green algae and potassium sulfate.- AP 3-89, 106-107

A. Vrabec (1989): Further experiences on potassium fertilization and control of blue algae with potassium sulfate.- AP 3-89, 108-109

G. Eggers (1989): Aspirin to combat algae? - AP 3-89, 94

W. Schwermer (1990): How do I get rid of my blue-green algae - AP 2-90, 51

B. Greger (1990): A topic without end - Algae in the aquarium - AP 2-90, 52-54

W. Rothmaler (2000): Exkursionsflora von Deutschland.- 3rd reviewed edition, Spektrum Akademischer Verlag Heidelberg, Berlin

Campbell et al. (2000) Biologie - first German edition, Spektrum Verlag

J.M. Huisman (2000): Marine Plants of Australia.- University of Western Australia Press, Canberra

M. Salisch (2001): Algae in freshwater aquariums: Not desired - but always latent - 2nd part and conclusion - Aquarium heute 2/2001, 37-40

J. Bogner (2004): A freshwater red alga in the aquarium - Aqua Planta 4-2004, 142

J. Sprung (2005): Algae - Problems and Solutions - Dähne-Verlag, Ettlingen

Gérard, C., Luc Brient, L., Le Rouzic, B. (2005): Variation in the Response of Juvenile and Adult Gastropods (Lymnaea stagnalis) to Cyanobacterial Toxin (Microcystin-LR) .- Inc. Environ Toxicol 20: 592 - 596

H. Streble, D. Krauter (2006): Life in a water drop - 10th edition, Kosmos Naturführer, Franckh-Kosmos Verlags-GmbH, Stuttgart

Lance, E. Brient, L., Bormans, M., Gérard, C. (2006): Interactions between cyanobacteria and Gastropods I. Ingestion of toxic Planktothrix agardhii by Lymnaea stagnalis and the kinetics of microcystin bioaccumulation and detoxification.- Aquatic Toxicology 79 (2006) 140-148

H. Streble, D. Krauter (2006): Life in a water drop - 10th edition, Kosmos Naturführer, Franckh-Kosmos Verlags-GmbH, Stuttgart

Zurawel, R. W., Charles F. B. Holmes, C.F.B., Prepas, E. E. (2006): Elimination of the Cyanobacterial Hepatotoxin Microcystin from the freshwater Pulmonate Snail Lymnaea stagnalis jugularis (SAY) .- Journal of Toxicology and Environmental Health, Part A, 69 (4)

H. Streble, D. Krauter (2006): Life in a water drop - 10th edition, Kosmos Naturführer, Franckh-Kosmos Verlags-GmbH, Stuttgart

H. Dittmar (2008): Algen.- Special Issue No. 4 Working Group Aquatic Plants in the VDA

B. Kaufmann (2010): Algae Primer - Aquarium - No problem with freshwater algae - Dähne Verlag

B. Kaufmann (2010): Algae primer - garden pond - No problem with freshwater algae - Dähne Verlag

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