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Prorocentrum balticum (Lohmann) Loeblich, 1970

Species Overview:

Prorocentrum balticum is an armoured, marine, planktonic, bloom-forming dinoflagellate species. This cosmopolitan species is commonly found in cold temperate to tropical waters world-wide.

Taxonomic Description:

P. balticum is a bivalvate species often observed in valve view. Cells are small (< 20 µm in diameter), and round to ovoid in valve view (Figs. 1-8), with two minute and distinct apical projections (Figs. 1,3). Although cells are nearly spherical, some have broad shoulders. In side view cells are round and slightly compressed (Fig. 8). Thecal valves are covered with many tiny interconnected spines (Figs. 1,2,7) which form narrow transverse rows on the intercalary band (Figs. 6,8). Many scattered rimmed pores are present on the cell surface (Fig. 2) (Dodge, 1975, Dodge, 1982, Toriumi, 1980, Steidinger and Tangen, 1996, Faust et al., 1999).

The relatively small periflagellar area is bordered by two minute apical spines (Figs. 1,3,6,7). The periflagellar area bears two pores of different sizes: one large and one small (Fig. 3) (Dodge, 1975, Toriumi, 1980, Steidinger and Tangen, 1996, Faust et al., 1999).

Morphology and Structure:

Prorocentrum balticum is a photosynthetic species with a round nucleus situated posteriorly (Dodge, 1975, Dodge, 1982, Toriumi, 1980).

Reproduction:

P. balticum reproduces asexually by binary fission.

Species Comparisons:

P. balticum is not easily distinguished from P. minimum and a critical assessment of its taxonomic status is still needed. Both are small species, valves covered with small spines, and periflagellar areas are relatively small with two pores. P. balticum is distinguished by its small size, its almost spherical shape (Toriumi, 1980), and its two minute apical projections (Faust et al., 1999).

Because of its small size, records of P. balticum may actually include closedly related, but undescribed species (Steidinger and Tangen, 1996).

Ecology:

P. balticum is a planktonic species. It is a neritic and oceanic species with world-wide distribution (Dodge, 1975, Dodge, 1982, Steidinger and Tangen, 1996). Cells are active swimmers.

This species has been reported to form red tides in many parts of the world (see Lassus, 1988). Many blooms have occurred in brackish water habitats (Tangen, 1980, Zotter, 1979, Edler et al., 1984) confirming Braarud's (1951) earlier growth experiments that revealed P. balticum's highest growth rates were at low salinities (10-15 o/oo).

Toxicity:

Although toxicity in P. balticum has never been confirmed, it has been associated with toxic red tides (Silva, 1956, Silva, 1963, Numann, 1957). Steidinger, 1979 regards it as a questionable toxic species.

Habitat and Locality:

Prorocentrum balticum is commonly found in marine waters all over the world: cosmopolitan in cold temperate to tropical waters (Dodge, 1975, Dodge, 1982, Steidinger and Tangen, 1996).

Prorocentrum balticum