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Prorocentrum micans Ehrenberg, 1834

Species Overview:

Prorocentrum micans is an armoured, marine, planktonic, bloom-forming dinoflagellate. This is a cosmopolitan species in cold temperate to tropical waters.

Taxonomic Description:

P. micans is a bivalvate species often observed in valve view. Cells of this species is highly variable in shape and size (Figs. 1,2,4-8) (see Bursa, 1959, Dodge, 1975). Cells are tear-drop to heart shaped, rounded anteriorly, pointed posteriorly, and broadest around the middle (Figs. 1,2,4-8). This species is strongly flattened with a well developed winged apical spine (10 µm long) (Figs. 1,3). Cells are medium-sized (35-70 µm long, 20-50 µm wide) with a length:width ratio usually less than two. The cell surface is rugose, covered with shallow minute depressions. Numerous tubular trichocyst pores are also present in short rows arranged radially (Figs. 1,7,8). Intercalary band is smooth and wide (Figs. 1,3,4) (Wood, 1954, Toriumi, 1980, Dodge, 1975, Dodge, 1982, Dodge, 1985, Fukuyo et al., 1990, Steidinger and Tangen, 1996, Faust et al., 1999).

The periflagellar area is a relatively small, shallow, broad triangular depression situated apically on the right valve off-center (Fig. 3). Two periflagellar pores are present: one large flagellar pore and one smaller auxiliary pore. Adjacent to the flagellar pore is a small, slightly curved periflagellar plate (Fig. 3). The large pointed apical spine lies adjacent to the periflagellar area directly opposite the periflagellar plate (Fig. 3) (Taylor, 1980, Toriumi, 1980).

Morphology and Structure:

P. micans is a photosynthetic species with two golden-brown chloroplasts situated peripherally. A large kidney-shaped nucleus is situated posteriorly. Two anterior vacuoles are usually present (Dodge, 1975, Dodge, 1982, Toriumi, 1980, Fukuyo et al., 1990).

Reproduction:

P. micans reproduces asexually by binary fission.

Species Comparison:

This species varies considerably in shape and size and may be confused with closely related species; e.g. P. gracile, P. scutellum and P. caribbaeum. P. gracile has a very strong winged apical spine, is not as broad, and has a length:width ratio usually larger than 2; P. scutellum is in the same size range as P. micans, but bears a shorter and broader apical spine (Dodge, 1975, Dodge, 1982). P. caribbaeum is also in the same size range, but is heart-shaped and broadest around the anterior end, whereas P. micans is more tear-drop shaped and broadest around the middle (Dodge, 1985, Faust, 1993a).

P. gracile and P. micans share two distinct features: a.) similar trichocyst pore pattern (Steidinger and Williams, 1970, Steidinger and Tangen, 1996); and b.) similar arrangement of apical spine: they lie adjacent to the periflagellar area (Toriumi, 1980).

Trichocyst pore number is highly variable in this species (Dodge, 1985): 83 pores per valve were illustrated for one P. micans specimen (Dodge, 1965), 101 pores per valve for another specimen (Dodge, 1985), and 139 pores per valve in yet another specimen (Sournia, 1986). Trichocyst pore morphology of this species resembles that of P. caribbaeum; however, the latter species has a much greater number of pores per valve: 145-203 (Faust, 1993a).

Ecology:

P. micans is a planktonic species commonly found in neritic and estuarine waters, but it is also found in oceanic environments; it is cosmopolitan in cold temperate to tropical waters. This species can tolerate very high salinity: populations have been reported from hypersaline salt lagoons (>90 o/oo) in the Caribbean islands (Steidinger and Tangen, 1996). P. micans is one of the most common and diversified species in the genus Prorocentrum. Cells are active swimmers (Dodge, 1982, Steidinger and Tangen, 1996).
This species forms extensive red tides in many parts of the world (Fukuyo et al., 1990, Faust et al., 1999).

Toxicity:

Although P. micans is capable of forming extensive blooms, it is usually considered harmless (see: Taylor and Seliger, 1979, Anderson et al., 1985, Graneli et al., 1990). It may excrete substances that inhibit diatom growth, but apparently these substances do not enter the food chain or affect organisms at higher trophic levels (Uchida, 1977).

There are only a few reports of P. micans having caused problems: shellfish kills in Portugal (Pinto and Silva, 1956) and South Africa (Horstman, 1981). Claims for toxicity of this species need confirmation. Early reports on P. micans being a paralytic shellfish poison (PSP) producer (Pinto and Silva, 1956) are unconfirmed, and recent incidents involving shellfish mortality have been attributed to oxygen depletion (Lassus and Berthome, 1988).

Habitat and Locality:

P. micans is commonly found in marine waters all over the world (Dodge, 1975).

Prorocentrum micans