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.

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 don 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.

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.

Small cytoplasmic bodies within the cells, called scintillons, are what give N. scintillans their bioluminescent property. Luciferase and luciferin are both found in those structures and it is the interaction of both these molecules that emits light.

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. Light is emitted when luciferin, an open-chain tetrapyrrole in dinoflagellates that is thought to be derived from chlorohyll, becomes oxidized by molecular oxygen, with the help of the catalyst luciferase. This process is called chemiluminescence because it is the convergence of chemical energy into light energy and it occurs inside the scintillons.

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 boom 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.

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. They found that the greatest environmental factor affecting the abundance and biomass of N. scintillans is diatom blooms.