Noctiluca scintillans, commonly known as the Sea Sparkle, and also published as Noctiluca miliaris, is a free-living non-parasitic marine-dwelling species of dinoflagellate that exhibits bioluminescence, when disturbed. The bioluminescent characteristic of N. scintillans is produced by a luciferin-luciferase reaction that takes place in thousands of spherically shaped organelles, called scintillons, located throughout the cytoplasm of this single-celled protist. This reaction occurs via a set of genes labeled a Lux operon. Nonluminescent populations within the genus Noctiluca lack these scintillons.
N. scintillans is a heterotroph (non-photosynthetic) that engulfs its food by phagocytosis, which includes plankton, diatoms, other dinoflagellates, as well as fish eggs and bacteria. Diatoms are often found in the vacuoles (internal membrane-bound storage compartments) within these single-celled creatures. These green non-feeding symbioses can grow photoautotrophically for generations. The diatom Thalassiosira sp. has been noted in the literature as a favored food source of these organisms.
N. scintillans can be found widely distributed throughout the world, often along the coast, in estuary, and shallow areas of the continental shelf that receive plenty of light which promotes the growth of the phytoplankton that make up a large portion of N. scintillans’s diet.
The size of the single-celled N. scintillans ranges from 200 to 2,000 µm in diameter, assuming the generally spherical shape. N. scintillans lacks the armor plates possessed by other types of dinoflagellates. And, unlike many other dinoflagellates, the chromosomes of the Noctiluca are not clearly visible and condensed throughout its lifecycle.
Noctiluca is unusual amongst dinoflagellates in appearing to have a diplontic life-cycle.
N. scintillans has a ventral groove within which is located a flagellum, an extension of the cell wall called a tooth, and a striated tentacle involved in ingestion that projects posteriorly. The flagellum does not move the organism and therefore the non-motile N. scintillans depends upon regulation of its buoyancy within the water column – perhaps by controlling its cellular concentration of ions and ammonia.
At least one study has shown that a string of mucus is produced by N. scintillans extending from the tip of the tentacle which then adheres to plankton as it ascends rapidly through concentrations of its prey in the water column.
High concentrations of their plankton food source that likely result from environmental conditions such as well-mixed nutrient-rich waters and seasonal circulation factors are implicated in population blooms of N. scintillans.
Swimmers may report being illuminated by a ghostly glow-in-the-dark plankton - a floating bloom of algae which fires up into a luminescent sparkle when disturbed. This gives Noctiluca scintillans the popular names "Sea Ghost" or "Fire of Sea".
Runoff from agricultural pollution may contribute to the severity of these blooms. However this is not required to cause explosive growth of Noctiluca scintillans.
Not all blooms associated with N. scintillans are red. The color of N. scintillans is in part derived from the pigments of organisms inside the vacuoles of N. scintillans. For instance, green tides result from N. scintillans populations that contain green-pigmented prasinophytes (green algae, Subphylum Chlorophyta) that are living in their vacuoles.
N. scintillans itself does not appear to be toxic, but as they feed voraciously on phytoplankton high levels of ammonia accumulate in these organisms which is then excreted by N. scintillans into the surrounding area which may add to the neurotoxic chemicals being produced by other dinoflagellates, such as Alexandrium spp. or Gonyaulax spp., that do result in the death of other aquatic life in the area.
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- Noctiluca scintillans - Guide to the Marine Zooplankton of south eastern Australia, Tasmanian Aquaculture & Fisheries Institute