Noctiluca scintillans

Noctiluca scintillans, also published as Noctiluca miliaris, is a free-living non-parasitic marine-dwelling species of dinoflagellate that exhibits bioluminescence. The bioluminescent characteristic of N. scintillans is produced by a luciferin-luciferase system located in thousands of spherically shaped organelles, or “microsources”, located throughout the cytoplasm of this single-celled protist. Nonluminescent populations within the genus Noctiluca lack these microsources.

Diet
N. scintillans is a heterotrophic (non-photosynthetic) organism that engulfs its food (phagotrophic) which primarily consists of plankton, including diatoms and 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. The diatom Thalassiosira sp. has been noted in the literature as a favored food source of these organisms.

Distribution
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.

Size
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.

Anatomy
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.

"Blooms"
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, known as “red tides”. Runoff from agricultural pollution may contribute to the severity of these blooms, but is not required to cause such events of explosive population growth.

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 Alexandrium spp. or Gonyaulax spp., that do result in the death of other aquatic life in the area.

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 plant algae, Subphylum Chlorophyta ) that are living in their vacuoles.

Evolutionary development
At least one study, based on small subunit (SSU) RNA data, found that the dinoflagellates are a monophyletic group and that within this group N. scintillans was among the earliest to diverge. Please see the phylogenetic tree below.

Another study, based on large subunit rRNA, supports the claim that heterotrophic species of dinoflagellates such as N. scintillans preceded the emergence of photosynthetic species. Photosynthetic species would have evolved by acquiring photosynthetic capability through secondary and even tertiary endosymbiosis.

N. scintillans is also placed within a classification scheme that has a class Diniferea, or Dinophyceae, which includes nonparasitic dinoflagellates that lack armor plating.