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Dinophysis fortii Pavillard, 1923

Species Overview:

Dinophysis fortii is an armoured, marine, planktonic dinoflagellate species. This species is a bloom-forming toxic species associated with DSP events. It has world-wide distribution in cold temperate waters, but is also found in subtropical to tropical waters.

Taxonomical Description:

Species in this genus are laterally compressed with a small, cap-like epitheca and a much larger hypotheca (dorso-ventral depth of epitheca is 1/2 to 2/3 of hypotheca). The shape of the cell in lateral view is the most important criterion used for identification (Taylor et al., 1995).

Cells of Dinophysis fortii are large, long and subovate ending in a broadly rounded posterior (a dorsal bulge) (Figs. 1-5). The posterior end is the widest (Figs. 1,2). The left sulcal list (LSL) is well developed and very long; it can extend up to 4/5 of the cell length (Figs. 1,3) (Abè, 1967a, Taylor et al., 1995, Steidinger and Tangen, 1996).

The thick thecal plates of the hypotheca are deeply areolated (Figs. 1,2), each areolae with a pore (Fig. 5). Cell size ranges: 56-83 µm in length and 43-58 µm in dorso-ventral width (at the base of the third rib of the LSL) (Abè, 1967a, Taylor et al., 1995, Larsen and Moestrup, 1992, Steidinger and Tangen, 1996).

Thecal Plate Description:

The small epitheca is made up of four plates. Well developed cingular lists, both anteriorly inclined, obscure the epitheca (Figs. 1-5). The anterior cingular list (ACL), which is wider than the posterior list (PCL), forms a wide and shallow cup with the epitheca as its bottom (Fig. 4) (Fukuyo et al., 1990, Taylor et al., 1995). The sulcus is comprised of several irregularly shaped plates. The flagellar pore is housed in the sulcal area. The LSL is very long, reticulated (Figs. 1,4) and supported by three ribs (Fig. 3) (Larsen and Moestrup, 1992, Taylor et al., 1995). A well developed triangular right sulcal list (RSL) is also present; it is approximately half the length of the LSL (Figs. 1,5) (Steidinger and Tangen, 1996).

The hypotheca, with four large plates, comprises the majority of the cell. The dorsal margin and antapical end are smoothly convex with a slight concavity near the cingulum (Fig. 3). The ventral margins are fairly straight, slanting at an angle of 110-120 degrees to the cingulum (Fig. 3) (Abè, 1967a, Larsen and Moestrup, 1992, Taylor et al., 1995, Steidinger and Tangen, 1996).

Morphology and Structure:

Dinophysis fortii is a photosynthetic species with large central chloroplasts (Fig. 4) and a terminal pyrenoid (Hallegraeff and Lucas, 1988, Larsen and Moestrup, 1992).

Reproduction:

D. fortii reproduces asexually by binary fission.

Remarks:

D. fortii is best identified by its wide rounded posterior and the presence of reticulations on the sulcal list (Larsen and Moestrup, 1992, Steidinger and Tangen, 1996). Variations in cell shape are mostly seen in the placement and size of the hypothecal dorsal bulge (Abè, 1967a).

Many authors consider Phalacroma to be synonymous with Dinophysis (Steidinger and Tangen, 1996).

Ecology:

D. fortii is a planktonic oceanic and neritic species (Abè, 1967a, Taylor et al., 1995, Steidinger and Tangen, 1996). It is a bloom-forming species; noxious blooms have been reported from Australia (Hallegraeff, 1987) and Japan (Yasumoto et al., 1980a, Osaka and Takabayashi, 1985, Igarashi, 1986). In northern Japan warm currents in spring and early summer carry populations of D. fortii landward where cells filter into coastal areas of intensive shellfish aquaculture (Taylor et al., 1995). Populations seem to be most abundant in early summer (Yasumoto et al., 1980b, Osaka and Takabayashi, 1985, Igarashi, 1986).

Observations of Miyazono and Minoda, 1990 suggest that this species prefers high salinity and low temperatures; however, they can tolerate lower salinities. Early studies of Ishimaru et al., 1988 suggest the capablity of D. fortii to prey upon cryptomonads.

Toxicity:

Dinophysis fortii is a known toxin producing species (Lee et al., 1989, Yasumoto, 1990, Larsen and Moestrup, 1992, Taylor et al., 1995, Steidinger and Tangen, 1996). It is the most noxious cause of DSP in Japanese waters. This species produces dinophysistoxin-1 (DTX1), dinophysistoxin-2 (DTX2), and okadaic acid (OA) (Lee et al., 1989, Yasumoto, 1990), although clones in warmer waters show very low toxicity (Taylor et al., 1995). Dinophysis fortii was the first species found to be associated with DSP; concentrations as low as 200 cells/L can cause human intoxication (Yasumoto et al., 1980b).

Habitat and Locality:

D. fortii is widely distributed in cold temperate waters world-wide, but is also found in subtropical to tropical areas (Abè, 1967a, Taylor et al., 1995, Steidinger and Tangen, 1996).

Dinophysis fortii