Chaetoceros belongs to the Bacillariophyta, Centrales, Biddulphiales, Chaetocerotaceae, and Chaetoceros.
In terms of morphological characteristics, the cells of Chaetoceros are flat and oval. The valve surface is usually oval, including broad oval or narrow oval, and very few are circular. The structure on the valve surface is extremely fine and delicate, and it is generally difficult to observe clearly. The valve surface is flat, convex or concave, and some have small spines. The long-axis girdle view is quadrangular, and the short-axis girdle view is rectangular. Cells often connect with adjacent cells through chaetae to form chains, or connect to each other on the valve surface to form chains. A few species are single cells. There are one to two or multiple chromatophores, mostly granular, distributed within the cells and the thick and hollow chaetae.
There are many species of Chaetoceros and they are widely distributed. It is one of the important planktonic diatoms in China’s coastal waters and occupies an important position in the coastal plankton population. They mostly live in seawater and brackish water, and very few exist in freshwater. Chaetoceros can grow and reproduce in an environment ranging from 10°C to 39°C, and the most suitable temperature range is 25°C to 35°C. Compared with other algae, Chaetoceros grows relatively fast, especially in spring and summer, often becoming the dominant group of phytoplankton.
The reproduction methods of Chaetoceros include forming auxospores, resting spores, and sexual reproduction. In the fossil record, the common ones are its resting spores.
Chaetoceros has an important position in marine plankton and is the bait organism of many marine animals. Therefore, its species composition and cell abundance have a direct or indirect important impact on other organisms and the marine environment in the marine ecosystem. However, although Chaetoceros is generally beneficial algae, it may also cause harm to water quality or aquatic organisms under certain circumstances. For example, the chaetae of Chaetoceros have barbs that may prick the gills of fish, thereby causing harm to farmed fish; some Chaetoceros are also prone to causing red tides.
Common species of Chaetoceros include:
Chaetoceros lorenzianus: The group chain is straight and short, and the valve surface is narrowly oval. The girdle view of the valve is rectangular and pointed. The valve mantle is mostly higher than one-third of the cell, and there is a very obvious depression at the intersection with the girdle band. The intercellular spaces are polygonal or oval. The chaetae are short, hard and straight, extending perpendicularly or obliquely from the cell chain axis. The intersection point of the chaetae base is short and thinner than other parts, and it becomes thicker from the intersection point. The cross-section is quadrangular with obvious four edges. There is a row of small spines on the edges, and developed coarse dot patterns cover the entire chaetae, especially at the end chaetae. It often forms a straight chain group of 2-5 cells, and each cell has 4-10 chromatophores. It is a coastal tropical and temperate species, widely distributed and often appears in warm seas. It is one of the dominant species in the four major sea areas of China.
Chaetoceros gracilis: The group chain is straight, the valve surface is oval, and the chaetae extend perpendicularly from the chain axis or gradually bend towards the chain end. The end chaetae are thick and curved like a sickle. The girdle is very narrow and the intercellular spaces are long and narrow. The chromatophores are large, usually one, with a central protein nucleus. This is a coastal eurythermal species, distributed in all sea areas of the world and also common along the coast of China.
Chaetoceros muelleri: The cells are small and thin-walled, mostly single cells, and individual groups composed of 2 or 3 cells. The valve surface is elliptical to circular, and the center is slightly protruded or slightly flat. The girdle view of the valve is rectangular to square, and the girdle band is not obvious. The chaetae are thin and long, with sharp ends, extending in parallel with the longitudinal axis. The chaetae at both ends of the valve surface are slightly S-shaped with the cell body as the center. There is one chromatophore, in the form of a flake. At present, it can be artificially cultivated in large quantities and used as a good bait for shellfish and shrimp.
The research of Chen Nansheng’s research group from the Institute of Oceanology, Chinese Academy of Sciences found that through long-term sequential sampling, high-throughput sequencing and metabarcoding analysis in the Jiaozhou Bay area, the advantages of the metabarcoding analysis method were demonstrated. This study discovered 25 species of Chaetoceros, including 10 species that have not been reported in Jiaozhou Bay, such as Chaetoceros neogracilis with smaller cells and Chaetoceros tenuissimus. At the same time, the study shows that the identification of several common Chaetoceros species in Jiaozhou Bay needs to be revised. For example, Chaetoceros compressus should be the morphologically similar species Chaetoceros contortus, and Chaetoceros diadema should be the morphologically similar species Chaetoceros rosporus. Among the 154 Amplicon Sequence Variants (ASVs) annotated as Chaetoceros, more than half of the ASVs (82 ASVs) were not annotated to known Chaetoceros species, representing unidentified Chaetoceros species (Chaetoceros sp.), indicating that the diversity of Chaetoceros in Jiaozhou Bay may be severely underestimated.
In the breeding of Penaeus vannamei, Chaetoceros was once used as the starter feed for shrimp larvae, but its adaptability to changes in light and temperature is weak, and it is prone to aging itself. If overfed, the dead Chaetoceros will produce a large amount of foam, affecting the survival rate of shrimp larvae and having an irreversible impact on water quality. Relatively speaking, Thalassiosira has strong adaptability to the environment, a long growth cycle and a slow aging rate, little pollution to the water body, and can also be artificially cultivated, and can be used as an alternative choice for feeding shrimp larvae.
In conclusion, as an important group of marine planktonic diatoms, Chaetoceros is of great significance to the marine ecosystem. In-depth study of its characteristics and ecological roles is helpful to better understand the marine ecological balance and the survival and reproduction mechanisms of related organisms. At the same time, in practical applications, it is also necessary to pay attention to the rational use of Chaetoceros to avoid possible negative impacts.
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Note: This picture is from https://x.com/umea_uni_marine/status/1649016239027527681?s=46
