Species Overview: Noctiluca scintillans is an unarmoured, marine planktonic dinoflagellate species. This large and distinctive bloom forming species has an associated with fish and marine invertebrate mortality events.
Taxonomic Description: Noctiluca scintillans is a distinctively shaped athecate species in which the cell is not divided into epitheca and hypotheca. Cells are very large, inflated (balloon-like) and subspherical (Figs. 1-4). The ventral groove is deep and wide, and houses a flagellum, a tooth and a tentacle (Figs. 1,2,4). Only one flagellum is present in this species and is equivalent to the transverse flagellum in other dinoflagellates (Fig. 1). The tooth is a specialized extension of the cell wall (Fig. 4). The prominent tentacle is striated and extends posteriorly (Fig. 4). Cells have a wide range in size: from 200-2000 Ám in diameter (Zingmark 1970; Dodge 1973; Dodge 1982; Lucas 1982; Fukuyo et al. 1990; Hallegraeff 1991; Taylor et al. 1995; Steidinger & Tangen 1996).
Morphology and Structure: Noctiluca scintillans is a nonphotosynthetic heterotrophic and phagotrophic dinoflagellate species; chloroplasts are absent and the cytoplasm is mostly colorless (Figs. 1, 2). The presence of photosynthetic symbionts can cause the cytoplasm to appear pink or green in color (Sweeney 1978). A number of food vacuoles are present within the cytoplasm. A large eukaryotic nucleus is located near the ventral groove with cytoplasmic strands extending from it to the edge of the cell (Fig. 2)(Zingmark 1970; Dodge 1982; Fukuyo et al. 1990; Hallegraeff 1991; Steidinger & Tangen 1996).
Reproduction: Noctiluca scintillans reproduces asexually by binary fission (Fig. 3) and also sexually via formation of isogametes. This species has a diplontic life cycle: the vegetative cell is diploid while the gametes are haploid. The gametes are gymnodinioid with dinokaryotic nuclei (Zingmark 1970).
Ecology: Noctiluca scintillans is a strongly buoyant planktonic species common in neritic and coastal regions of the world. It is also bioluminescent in some parts of the world. This bloom-forming species is associated with fish and marine invertebrate mortality events. N. scintillans red tides frequently form in spring to summer in many parts of the world often resulting in a strong pinkish red or orange discoloration of the water (tomato-soup). Blooms have been reported from Australia (Hallegraeff 1991), Japan, Hong Kong and China (Huang & Qi 1997) where the water is discolored red. Recent blooms in New Zealand were reported pink with cell concentrations as high as 1.9 X 106 cells/L (Chang 2000). In Indonesia, Malaysia, and Thailand (tropical regions), however, the watercolor is green due to the presence of green prasinophyte endosymbionts (Sweeney 1978; Dodge 1982; Fukuyo et al. 1990; Hallegraeff 1991; Taylor et al. 1995; Steidinger & Tangen 1996). This large cosmopolitan species is phagotrophic, feeding on phytoplankton (mainly diatoms and other dinoflagellates), protozoans, detritus, and fish eggs (Fig. 2)(Dodge 1982; Fukuyo et al. 1990; Hallegraeff 1991; Taylor et al. 1995; Steidinger & Tangen 1996).
Toxicity: Toxic blooms of N. scintillans have been linked to massive fish and marine invertebrate kills. Although this species does not produce a toxin, it has been found to accumulate toxic levels of ammonia which is then excreted into the surrounding waters possibly acting as the killing agent in blooms (Okaichi & Nishio 1976; Fukuyo et al. 1990). Extensive toxic blooms have been reported off the east and west coasts of India, where it has been implicated in the decline of fisheries (Aiyar 1936; Bhimachar & George 1950).
Habitat and Locality: Noctiluca scintillans is a cosmopolitan species distributed world wide in cold and warm waters. Populations are commonly found in coastal areas and embayments of tropical and subtropical regions (Dodge 1982; Fukuyo et al. 1990; Hallegraeff 1991; Taylor et al. 1995; Steidinger & Tangen 1996).
Remarks: This species is frequently referred to as N. miliaris although Macartney's specific name has priority. Taylor (1976) suggests that the simplest solution to the problem of nomenclature is to accept the priority of the 'scintillans' especially as this has been used by two major works (Kofoid & Swezy 1921; Lebour 1925).