NOCTILUCAS: CHARACTERISTICS, HABITAT, FEEDING, REPRODUCTION - BIOLOGY - 2025

Noctiluca is a genus of single-celled marine eukaryotic organisms belonging to the phyllum Dinoflagellata (dinoflagellates). The genus is made up of a single species, N. scintillans, which is called sea spark because it is bioluminescent.

Noctilucas are microscopic organisms with heterotrophic feeding, that is, they need to obtain their food from other organisms. They have a long tentacle, at the base of which there is a small flagellum. They are relatively common in coastal areas in various parts of the world.

Noctiluca scintillans. Taken and edited from Maria Antónia Sampayo, Institute of Oceanography, Faculdade Ciências da Universidade de Lisboa, via Wikimedia Commons.

When Noctiluca populations are very large, during night hours the bioluminescence of these organisms can be seen from far away, showing some of the most beautiful phenomena in nature.

characteristics

They are dinoflagellates that have a large tentacle, at the base of which has a short and rudimentary flagellum. However, none of these appendages use them for locomotion, which implies that their mobility in the water column depends on regulating buoyancy, probably changing their ionic concentration.

They have a globose or spherical shape, with a gelatinous appearance, they also have a well-defined central nucleus, they also have several food vacuoles.

They do not photosynthesize, so they do not have chloroplasts. They can measure between 200 and 2000 micrometers in diameter. They have a very peculiar molecule called luciferin, which in the presence of oxygen, and catalyzed by the enzyme luciferase, produces a phenomenon called bioluminescence.

Scientists have separated the Noctiluca scintillans species into two groups that are not taxonomically valid, but have particular characteristics:

Red Noctiluca

Their populations are strictly heterotrophic, and they are a fundamental part of the phytophages that feed on marine phytoplankton in the regions where they inhabit, ranging from temperate to subtropical regions.

Noctiluca green

Their populations have a photosynthetic symbiont (Pedinomonas noctilucae) that provides them with food in a certain way in an autotrophic way. However, they are also heterotrophs that feed on other microorganisms when required.

Their distribution is somewhat more restricted and they have been observed off the coasts of India, the Arabian Sea and the Red Sea.

Taxonomy

The genus Noctiluca is located within the Cromista kingdom, Mizozoa phyllum, Dinoflagellata infraphyllum and the Dinophyceae family. It is a monospecific genus, that is, it contains only one species.

Due to its wide distribution, its ecological and physiological behavior, several researchers came to think, and even publish, that there was more than one species within the genus Noctiluca; However, at present all these species are considered synonymous with Noctiluca scintillans

Habitat

Noctiluca are strictly marine organisms, they live in the water column and have a wide worldwide distribution. They have been reported, for example, from the north of Brazil to Florida (USA), in the American Pacific Ocean, coasts of Africa, northern Europe, part of the Indo-Pacific and Australia, among other locations.

This wide distribution indicates that Noctiluca is an “euri” organism, that is, its populations have a wide tolerance margin to multiple physical, chemical and biological factors. For example, they live in areas with temperatures ranging from 10 to 30 ºC approximately, they tolerate high salinities, but they do not live in estuaries.

The red noctilucas live in environments with temperatures between 10 and 25 ºC, while the green ones prefer warmer habitats, between 25 and 30 ºC. Both have preferences for diatoms and when phytoplanon blooms of these microalgae occur, the presence of Noctiluca also increases.

Feeding

Noctilucas are heterotrophic organisms that engulf their prey by phagocytosis. They are great predators of plankton throughout the water column. Noctilucas have been determined to have food preferences for diatoms of the genus Thalassiosira.

However, these organisms prey on a great diversity of prey, ranging from fish and copepod eggs, adult copepods, invertebrate larvae, tintinids, to other dinoflagellates and other diatom species.

Another form of feeding of noctilucas is the autotrophic. It has been determined that the "green" Noctiluca absorbs a species of primitive microalgae (Pedinomonas noctilucae), which later inhabits it as a symbiont.

The photosynthetic activity of the microalgae provides food for the noctilucas. However, this "green" Noctiluca can feed on other individuals when the feeding conditions require it.

Reproduction

Noctilucas have two types of reproduction, sexual and asexual:

Asexual

The asexual type of reproduction does not involve the intervention of female and male gametes, but other mechanisms such as budding, fragmentation or fission. In Noctiluca, asexual reproduction is by fission.

During the fission process, the progenitor cell duplicates its genetic material (DNA) and then gives rise, by cytokinesis, to two (binary fission) or more (multiple fission) daughter cells. In noctilucas both binary and multiple fission occur.

Sexual

This type of reproduction involves the presence of female and male gametes for the production of offspring . Sexual reproduction in Noctiluca presents a 12-step gametogenesis.

During sexual reproduction, a fraction of the population spontaneously converts into gametogenic cells. These cells divide their nuclei twice without a division of the cytoplasm; the nuclei product of this division are called progametes.

The progametes migrate towards the cell margins with a part of the cytoplasm and once there they divide synchronously 6 to 8 times. When this division reaches between 200 and more than 1000 progametes, they are released from the mother cell as biflagellate zoospores.

As a result of the presence of asexual (binary and multiple fission) and sexual reproduction (gametogenesis), noctilucas can colonize, adapt and survive in dynamic or fluctuating environments, being highly competitive against other plankton organisms.

Blooms of

Blooms, also called phytoplankton blooms, are biological phenomena that occur when the availability of nutrients in a marine area (in this case) is very high and favors the rapid multiplication of microorganisms, especially phytoplankton.

When these blooms occur, noctiluca populations also increase, because their food is available in large quantities.

Noctilucas bloom is usually associated with red tides, due to the color that the water acquires when their populations increase rapidly. However, there is no relationship, or at least not direct, between the toxic red tide of some dinoflagellates and the Noctiluca blooms.

Coastal bioluminescence of Noctiluca scintillans. Taken and edited from LucasBento, from Wikimedia Commons.

Noctilucas are bioluminescent organisms, their blooms make the coasts light up thanks to the movement of the waves, which excites the cells and causes them to produce a short flash of light. In some places they have a high tourist attraction.

References

1. K. Rogers. Noctiluca. Dinoflagellate genus. Recovered from britannica.com.
2. JJ Bustillos-Guzmán, CJ Band-Schmidt, DJ López-Cortés, FE Hernández-Sandoval, E. Núñez-Vázquez & I. Gárate-Lizárraga (2013). Grazing of the dinoflagellate Noctiluca scintillans on the paralytic toxin-producing dinoflagellate Gymnodinium catenatum: Does grazing eliminate cells during a bloom? Marine Sciences.
3. Noctiluca scintillans. Recovered from en.wikipedia.org
4. Noctiluca. Recovered from es.wikipedia.org.
5. NE Sato, D. Hernández & MD Viñas (2010). Eating habits of Noctiluca scintillans in coastal waters of the Province of Buenos Aires, Argentina. Latin American Journal of Aquatic Research.
6. PJ Harrison1, K. Furuya, PM Glibert, J. Xu, HB Liu, K. Yin, JHW ​​Lee, DM Anderson, R. Gowen, AR Al-Azri & AYT Ho (2011). Geographical distribution of red and green Noctiluca scintillans. Chinese Journal of Oceanology and Limnology.
7. T. Kitamura & H. Endoh. Gametogenesis in Noctiluca scintillans under light-dark cycle. Recovered from protistology.jp.