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 (popularly known as mareel). Its bioluminescence is produced throughout the cytoplasm of this single-celled protist, by a luciferin-luciferase reaction in thousands of spherically shaped organelles, called scintillons. Nonluminescent populations within the genus Noctiluca lack these scintillons.
N. scintillans is a heterotroph (non-photosynthetic) that engulfs by phagocytosis food which includes plankton, diatoms, other dinoflagellates, 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 single-celled N. scintillans is roughly spherical and ranges from 200 to 2,000 µm in diameter. Unlike other types of dinoflagellates, it lacks armor plates, and unlike many other dinoflagellates its chromosomes are not clearly visible and condensed throughout its lifecycle.
N. scintillans has a ventral groove that holds 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, so the non-motile N. scintillans depends on 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 N. scintillans produces a string of mucus extending from the tip of the tentacle which then adheres to plankton and ascends rapidly through concentrations of its prey in the water column.
N. scintillans populations can exhibit high concentrations due to high concentrations of the plankton on which they feed, which are likely due to environmental conditions such as well-mixed nutrient-rich waters, seasonal circulation and runoff from agricultural pollution.
The glow produced by N. scintillans organisms can be perceived by humans as ghostly colored glow or bloom in the water, which appears when the water is disturbed. This gives Noctiluca scintillans the popular names "sea ghost" or "fire of sea".
Bloom color partly derives from the pigments of organisms inside the vacuoles of N. scintillans. Blooms are often red. Green tides result from N. scintillans populations having green-pigmented prasinophytes (green algae, Subphylum Chlorophyta) living in their vacuoles.
N. scintillans itself does not appear to be toxic, but as it feeds voraciously on phytoplankton, it accumulates and excretes high levels of ammonia into the surrounding area. This may add to the neurotoxins produced by other dinoflagellates, such as Alexandrium spp. or Gonyaulax spp., that kill off other aquatic life in the area.
DNA sequence comparisons suggest that the closest relative of the genus Noctiluca is Spatulodinium. Spatulodinium pseudonoctiluca seems to be closer related to N. scintillans than to other Spatulodinium species.
N. scintillans is also placed within a classification scheme that has a class Diniferea, or Dinophyceae, which includes nonparasitic dinoflagellates that lack armor plating.
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- Noctiluca scintillans - Guide to the Marine Zooplankton of south eastern Australia, Tasmanian Aquaculture & Fisheries Institute