Noctiluca scintillans

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Noctiluca scintillans
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Scientific classification
Domain: Eukaryota Genus: Noctiluca Species: N. scintillans
Binomial name
Noctiluca scintillans

Description and Significance

Noctiluca scintillans, also known as the sea sparkle, is a single-celled dinoflagellate that exhibits bioluminescence. They are free-living marine plankton, which range between 200-2000 micrometers in diameter. They are found mostly in estuaries and other coastal regions and can be found in both warm and cold waters. N. scintillans are heterotrophic and non-photosynthetic, meaning they receive their carbon from organic compounds and receive their energy through the ingestion of organic substances. They don’t have any chloroplasts so, their cytoplasm is relatively clear. N. scintillans are non-motile, even though they possess a flagellum, and only move vertically by changing their buoyancy using gas vacuoles. N. scintillans can reproduce asexually, by binary fission, and sexually, using isogametes through a diplontic lifecycle.

The bioluminescent property of N. scintillans is a tourist attraction for many countries throughout the world. People would take boat rides and watch these dinoflagellates emit flashes of blue light when disturbed, giving them the name sea sparkle.

Genome and Structure

Many studies have been done on the luciferase gene within the scintillons of N. scintillans. They have found that N. scintillans is genetically distinct from the other six bioluminescent dinoflagellates that have been studied, because the N-terminus is missing a ~100aa sequence. Still the N-terminus is closely related to the other bioluminescent dinoflagellates. The C-terminal end of this gene, however, is closely related to a separate gene in a photosynthetic dinoflagellate. It is as if these two genes in the photosynthetic species were fused in N. scintillans. Studies of the 18S ribosomal DNA of N. scintillans, also suggested that they were one of the first bioluminescent species to branch off because their genomic sequence is most closely related to the ancestral gene.

Bioluminescence

N. scintillans may use bioluminescence for many different purposes. It could be used as a defense against predators, an offensive strategy to keep away other predators from their prey, or as a means of communication. They emit light, on a circadian rhythm and when they are disturbed, as a flash of bright blue light for no more than a second. Luciferin, an open-chain tetrapyrrole in dinoflagellates that is thought to be derived from chlorophyll, becomes oxidized by molecular oxygen, with the help of the catalyst luciferase, to produce an inactive oxyluciferin and light. This process is called chemiluminescence because it is the convergence of chemical energy into light energy and it occurs within small cytoplasmic bodies called scintillons, where both luciferin and luciferase are stored. Bioluminescence is triggered by a drop of pH within the cytoplasm.

Cell Structure and Metabolism

N. scintillans has a round, balloon-like, body shape and is unarmored, meaning it does not have a protective shell. Since they do not photosynthesize they do not contain chloroplasts, and thus are fairly clear. The red and green color usually associated with this species during red and green tides, are due to the pigments of the photosynthetic symbionts within the vacuoles of N. scintillans and not the species itself. N. scintillans has a ventral groove that runs through it's body which contains the flagellum, a tooth and a tentacle. They also have a mouth-like structure called the cytostome, which is used to capture and consume prey. Their nuclues contains chromosomes that are always condensed (dinokaryotic), except during interphase.

N. scintillans is a phagotrophic species with many food vacuoles found throughout it's cytoplasm. They engulf smaller marine species such as diatoms, protozoans, fish eggs, and certain bacteria, and then digest them in these food vacuoles. N. scintillans also contains gas vacuoles, which are filled with ammonia gas, that allow them to control their buoyancy.

Ecology and Pathology

N. scintillans are found mostly in coastal areas, in both temperate and tropical waters. Their population density has been found to be dependent on food availability, which is why they tend to stay in shallow, coastal areas, where phytoplankton thrive. They are also a major factor on the population density of zooplankton.

N. scintillans are sometimes known to have a large population blooms known as red or green tides (depending on what color endosymbionts are present in their vacuoles.) These tides cause the death of many marine animals. N. scintillans does not, however, release exotoxins like many other dinoflagellates do. Instead, it is believed that they kill these animals by suffocation due to the release of ammonia and carbon dioxide, causing anoxic water conditions.

Current Research

Ride Tide of Noctiluca Scintillans and it's Impact on the Coastal Water Quality of the Near-Shore Waters, Off the Rushikulya River, Bay of Bengal

This study is being conducted to check the quality of the water after red tides of N. scintillans. The researchers take samples of the water from different depths and determine the quality of the water by checking temperature, salinity, nitrate, nitrite and phosphate concentration. They found drops in water temperature during bloom periods, as well as a decrease of dissolved oxygen during blooms. Phosphate, nitrate and silicate levels increased during bloom periods while nitrite levels decreased. However, they found no correlation between the salinity content of the water and the formations of red tides.

Seasonality of the Bloom-Forming Hetertrophic dinoflagellate Noctiluca Scintillans in the Gulf of Oman in Relation to Environmental Conditions

This study is being conducted to find what environmental factors contribute to the population blooms of Noctiluca scintillans. They are checking hydrographic and biological factors as well as other factors such as wind intensity. The optimum temperature for the growth of N. scintillans was between 10-28^oC and the optimum salinity was between 28-36%.