Identifying Harmful Marine Dinoflagellates

Dinophysis norvegica
Claparède et Lachmann, 1859
Plate 16, Figs. 1-6

Species Overview: Dinophysis norvegica is an armoured, marine, planktonic dinoflagellate species. This species is a bloom-forming toxic species associated with DSP events. It is commonly found in cold neritic waters.

Taxonomic 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). However, size and shape varies considerably in this species (Larsen & Moestrup 1992).
Cells of Dinophysis norvegica are generally large, ovoid and robust (Fig. 1). The posterior end tapers to a triangular shape (Figs. 1-6). The antapex is pointed (Fig. 2) or slightly rounded (Fig. 3), and occasionally with small knob-like protrusions that may extend along the rounded dorsal margin (Figs. 1, 4, 5). This species is widest at or slightly above the middle of the cell (Fig. 4). The left sulcal list (LSL) extends about 2/3 of cell length (Balech 1976; Dodge 1982; Larsen & Moestrup 1992; Taylor et al. 1995; Steidinger & Tangen 1996).
The thick thecal plates are coarsely areolated; areolae are large and each with a pore (Figs. 1, 3, 6). Cell size ranges: 48-80 µm in length and 39-70 µm in dorso-ventral width (widest in the middle)(Balech 1976; Dodge 1982; Taylor et al. 1995; Steidinger & Tangen 1996).

Nomenclatural Types:
Holotype: Dinophysis norvegica Claparčde and Lachmann, 1859: 407, plate 20, fig. 19
Type Locality: North Sea: Fjord of Bergen, Glesnesholm, Norway
Synonyms: Dinophysis debilior Paulsen, 1949

Thecal Plate Description: The small epitheca is low, flat or weakly convex, and is obscured by cingular lists. It is made up of four plates with a sinuous sculpture (Balech 1976; Dodge 1982; Taylor et al. 1995).
The cingulum is made up of four unequal plates, all with pores. The cingulum bears two well sculptured lists: an anterior cingular list and a posterior cingular list (Fig. 1). In general, they are covered with irregular coarse or fine sinuous lines or reticulations (Figs. 1, 6). Both lists are projected anteriorly (Balech 1976; Dodge 1982).
The sulcus is comprised of several irregularly shaped plates. The flagellar pore is housed in the sulcal area. The LSL, supported by three ribs that radiate outward, is relatively narrow (average maximum width = 10 µm) and curved to the right between the second and third rib (Fig. 1). The first and second ribs project anteriorly; the third rib is curved or straight and projects posteriorly (Figs. 1, 5, 6). The third rib is located at the mid-point of the cell or just above it (Fig. 4). The sulcal lists may have surface ornamentation, or they may be smooth (Balech 1976; Dodge 1982; Steidinger & Tangen 1996).
The hypotheca, with four large plates, comprises the majority of the cell. The dorsal margin is smoothly convex to the antapex, while the ventral margin is straight or convex up to the third sulcal rib, then becomes concave or straight to the antapical end (Figs. 1-6) (Balech 1976; Dodge 1982; Larsen & Moestrup 1992).

Morphology and Structure: Dinophysis norvegica is a photosynthetic species with yellow chloroplasts and a posteriorly oriented nucleus (Fig. 5) (Schiller 1933; Larsen & Moestrup 1992).
Dimorphic cells of D. norvegica were found in Danish waters: one theca half was smaller with rounded margins and a pointed antapex (D. norvegica f. crassior); the other half was larger with a distinct concave indentation on the lower third of the ventral margin and a more rounded antapex (D. norvegica f. debilor). It is highly probable that these cells represent a stage in gametogenesis. Or they may be examples of natural variation within the species (Hansen 1993).

Reproduction: D. norvegica reproduces asexually by binary fission. Hansen (1993) speculates that sexual reproduction, with sexual dimorphism, is part of the life cycle for this species.

Ecology: D. norvegica is a planktonic neritic species (Schiller 1933; Taylor et al. 1995; Steidinger & Tangen 1996). Blooms have been reported from the British Isles (Dodge 1977), Scandinavia (Dahl & Yndestad 1985; Krogh et al. 1985) and the U.S. (Freudenthal & Jijina 1985). Cell numbers of about 80,000cells/L have been reported from Denmark (Larsen & Moestrup 1992). Jacobson & Andersen (1994) found a high number of food vacuoles in cells of Dinophysis norvegica and deduced that mixotrophy is an important aspect of its biology. They speculate that this species feeds by way of a peduncle (myzocytosis), the feeding mode used by the heterotrophic species Dinophysis rotundata and D. hastata (Schnepf & Deichgraber 1983). The peduncle passes through the cytostomal opening in the theca when the cell is feeding (Jacobson & Andersen 1994).

Toxicity: D. norvegica is a known toxin producer associated with diarrhetic shellfish poisoning (DSP) events. Cembella (1989), Lee et al. (1989) and Yasumoto (1990) reported Dinophysistoxin-1 (DTX1) and okadaic acid (OA) production from this species.

Species Comparison: Dinophysis norvegica is very similar to D. acuta in shape, and thus can easily be misidentified. Balech (1976) found that the plate patterns of these two species are very similar, but are more variable in D. norvegica. These species can be differentiated by their size (although they overlap) and deepest position: D. acuta is larger and widest below the mid-section, whereas D. norvegica is smaller and widest in the middle region of the cell (Balech 1976; Dodge 1982; Dodge 1985; Larsen & Moestrup 1992; Taylor et al. 1995; Steidinger & Tangen 1996).
Other differences between the two species include: D. acuta has a longer left sulcal list relative to its cell length (Balech 1976); D. norvegica is more pointed at the antapex and lacks the hypothecal bulge evident in D. acuta (Dodge 1985); the LSL in D. norvegica twists to the right between the second and third rib, and appears narrower than in D. acuta (Balech 1976; Dodge 1982).

Habitat and Locality: D. norvegica is widely distributed in cold, temperate northern waters (Dodge 1985; Steidinger & Tangen 1996).

Remarks: D. norvegica is considerably variable in size and shape (Schiller 1933; Balech 1976). A number of forms and varieties have been described: D. norvegica var. debilor Paulsen and D. norvegica var. crassior Paulsen, both of which were subsequently raised to species level (Paulsen 1949). Solum (1962) later considered them as different forms of D. norvegica.
Many authors consider Phalacroma to be synonymous with Dinophysis (Steidinger & Tangen 1996).

Figure 1: Morphology of a Dinoflagellate