Species Profile: Tetraselmis suecica

Tetraselmis suecica

Members of the genus Tetraselmis are among the most commonly cultured microalgae species in aquaculture.  Within this genus, Tetraselmis suecica is the species generally cultured as an aquaculture feed and will be the species referred to in this article as Tetraselmis.  In our experience, Tetraselmis is second only to Nannochloropsis oculata as an ideal aquaculture feed for clownfish culture.  Both are very nutritious and easy to culture, but Nannochloropsis has an extremely strong cell wall that makes it more resilient and suitable for long-term storage.  However, we consider Tetraselmis to be the top all-around algae for general aquaculture use.  The strong cell wall that makes Nannochloropsis so resilient also makes it difficult for many organisms to access the nutrients inside.  Tetraselmis is much easier for organisms to digest and is widely used in applications such as bivalve and crustacean culture where Nannochloropsis is largely unsuitable.   Based on casual observation and experiences, we suspect that Tetraselmis is superior to Nannochloropsis as a supplemental feed to reef aquaria and corals for the same reason, although we have no measurable data to support that idea. 

General Characteristics

Tetraselmis is a true green-algae classified in the phylum Chlorophyta.  Chlorophytes are similar to land plants in that they utilize both chlorophyl a and b and store energy in their plastids as starches.  Tetraselmis cells are comparatively much larger than many other commonly cultured microalgae, ~six times larger by cell volume and ~10 times greater by organic weight than Isochrysis, although Tetraselmis has only ¼ the lipid concentration of Isochrysis (Helm et al., 2004).  Tetraselmis are motile algae using four flagella for locomotion. 

Culture Characteristics

Tetraselmis has several characteristics that make it an excellent species for aquaculture, not the least of which is ease of culture.  Tetraselmis can be cultured in standard nutrient media such as Guillard’s f/2 media.  It can be grown in salinities ranging from nearly freshwater, to salinities of 50ppt, although ideal growth occurs near that of seawater, 25-35ppt (Fabregas et al., 2004). 

Nutritional Profile

The major long chain polyunsaturated fatty acid produced by Tetraselmis is eicosapentaenoic acid (EPA) which is produced along with C16 to C18 fatty acids (Pugkaew et al., 2019).  It deficient in docosahexaenoic acid (DHA, C22:6).  Despite this deficiency, it is sufficiently nutritious for clownfish culture, but for more fastidious species it is usually fed in conjunction with Isochrysis or other species that produce DHA. 

Additional Culture and Use Information

With chlorophyl characteristics similar to land plants, Tetraselmis responds well to standard LED grow lights, especially those heavy in the red spectra.  Although these algae are motile, they are easy to concentrate by refrigerating a harvested culture for a few days then decanting the supernatant, retaining the settled cells at the bottom.  The resulting slurry can be kept refrigerated for several weeks.  These species are also capable of heterotrophic/mixotrophic culture in which a carbon source (glucose, peptone, glycerine etc.) is added to the culture media.  While culture harvest densities may be more than double that of photoautotrophic culture (Azma et al., 2011), this culture method is of more utility in biofuel and other mass production settings.  The added carbon predisposes cultures to bacterial blooms and crashes if not managed closely. 

References

Azma, M., Mohamed, M. S., Mohamad, R., Rahim, R. A., & Ariff, A. B. (2011). Improvement of medium composition for heterotrophic cultivation of green microalgae, Tetraselmis suecica, using response surface methodology. Biochemical Engineering Journal53(2), 187-195.

Bong, S. C., & Loh, S. P. (2013). A study of fatty acid composition and tocopherol content of lipid extracted from marine microalgae, Nannochloropsis oculata and Tetraselmis suecica, using solvent extraction and supercritical fluid extraction. International Food Research Journal20(2).

Dörner, J., Carbonell, P., Pino, S., & Farías, A. (2014). Variation of fatty acids in Isochrysis galbana (T-Iso) and Tetraselmis suecica, cultured under different nitrate availabilities. Fisheries and Aquaculture Journal5(3), 1.

Fabregas, J., Abalde, J., Herrero, C., Cabezas, B., & Veiga, M. (1984). Growth of the marine microalga Tetraselmis suecica in batch cultures with different salinities and nutrient concentrations. Aquaculture42(3-4), 207-215.

Helm, M. M., Bourne, N., & Lovatelli, A. (2004). Hatchery culture of bivalves: a practical manual. Food and Agriculture Organization of the United Nations. Fisheries Technical Paper, (471).

Pugkaew, W., Meetam, M., Yokthongwattana, K., Leeratsuwan, N., & Pokethitiyook, P. (2019). Effects of salinity changes on growth, photosynthetic activity, biochemical composition, and lipid productivity of marine microalga Tetraselmis suecica. Journal of Applied Phycology31(2), 969-979.