Identifying Harmful Marine Dinoflagellates

Dinophysis acuminata
Claparède et Lachmann, 1859
Plate 11, Figs. 1-6

Species Overview: Dinophysis acuminata is an armoured, marine, planktonic dinoflagellate species. It is a toxic species associated with DSP events and is commonly found in coastal waters of the northern Atlantic and Pacific Oceans.

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 1/3 to 1/2 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 acuminata are small to medium, almost oval or elliptical in shape (Figs. 1-5). The shape can vary from rotund to long and narrow in lateral view. A well-developed left sulcal list (LSL) extends beyond the midpoint of the cell (1/2 to 2/3 of cell length) (Figs. 1-3). The antapex is rounded, and cells are commonly found with two to four small knob-shaped posterior protrusions; sometimes well-developed and sometimes not (Figs. 2-5) (Balech 1976; Hallegraeff & Lucas 1988; Taylor et al. 1995; Steidinger & Tangen 1996).
The thick thecal plates are covered with prominent circular areolae, each with a pore (Fig. 2). These markings can vary depending on the age of the cell. The variations can range from only pores (Fig. 3), to depressions with scattered pores (Fig. 1), to depressions each with a pore, to areolae each with a pore (Fig. 2). Pores are not found in the megacytic zone (Fig. 3). Cell size ranges: 38-58 µm in length and 30-40 µm in dorso-ventral width (widest near middle of cell) (Lebour 1925; Abč 1967; Dodge 1982; Fukuyo et al. 1990; Larsen & Moestrup 1992; Taylor et al. 1995; Steidinger & Tangen 1996).

Nomenclatural Types:
Holotype: Dinophysis acuminata Claparčde and Lachmann, 1859: 408, plate 20, fig. 17
Type Locality: North Sea: Norway
Synonyms: Dinophysis lachmannii Paulsen, 1949
Dinophysis borealis Paulsen, 1949
Dinophysis boehmii Paulsen, 1949

Thecal Plate Description: The epitheca is slightly convex and inclined ventrally (Figs. 1-4). Made up of four plates, it is not visible in lateral view (Balech 1976; Hallegraeff & Lucas 1988; Taylor et al. 1995; Zingone et al. 1998).
The cingulum is made up of four unequal plates, and is bordered by two well-developed lists: an anterior cingular list (ACL), often with ridges, and a smooth posterior cingular list (PCL) (Fig. 1). The dorsal end of the cingulum is concave, strongly inclined and (Figs. 1, 6) (Balech 1976; Zingone et al. 1998).
The sulcus is comprised of four irregularly shaped plates. The flagellar pore is housed in the sulcal area. The LSL, supported by three ribs, is rather narrow and often sculptured with reticulated ribs, lines and areolae (Balech 1976; Taylor et al. 1995; Zingone et al. 1998). The third rib on the left sulcal list is the longest, and is usually strongly curved posteriorly (Figs. 1, 4, 6). Sulcal plate development is highly variable in this species (Balech 1976).
The hypotheca, with four large plates, comprises the majority of the cell. The dorsal margin is more or less evenly convex (Figs. 1, 2, 4). The ventral margin is rarely convex; it is generally oblique and flat (Figs. 2-5)(Balech 1976). The antapex is ventrally off-center (Figs. 2-5)(Abč 1967).

Morphology and Structure: Dinophysis acuminata is a photosynthetic species with large chloroplasts, a posterior pyrenoid, and a large central nucleus (Hallegraeff & Lucas 1988; Zingone et al. 1998).

Reproduction: D. acuminata reproduces asexually by binary fission. Mackenzie (1991) reported sexual reproduction via the fusion of anisogamous gametes.

Ecology: D. acuminata is a planktonic toxic bloom-forming species (Taylor et al. 1995; Steidinger & Tangen 1996). The most extensive blooms have been reported from the summer and fall months (Kat 1989; Taylor et al. 1995). Blooms have been reported from many parts of the world (see Kat 1985); however, they have been particularly extensive with cell concentrations less than 40,000 cells/L (Kat 1985; 1989). Blooms are often associated with toxicity of shellfish (Taylor et al. 1995). Jacobson and Andersen (1994) found a high number of food vacuoles in cells of Dinophysis acuminata 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 & DeichgrAbčr 1983). The peduncle, the proposed feeding apparatus, passes through the cytostomal opening in the theca when the cell is feeding (Jacobson & Andersen 1994).

Toxicity: D. acuminata is a toxic species that has been found to produce okadaic acid (OA) (Cembella 1989; Lee et al. 1989) causing diarrhetic shellfish poisoning (DSP) (Kat 1985). Toxicity can vary considerably among seasons and areas where it blooms (Taylor et al. 1995). This species can cause shellfish toxicity at very low cell concentrations (as low as 200 cells/L)(Lassus et al. 1985). Hoshiai et al. (1997), however, reported a case of nontoxic mussels in Kesennuma Bay, northern Japan, in the presence of high concentrations of D. acuminata cells.

Species Comparison: D. acuminata can be confused with D. sacculus, D. norvegica, D. ovum and D. punctata, but is most often misidentified as D. sacculus (Steidinger & Tangen 1996; Zingone et al. 1998). The major difference between D. acuminata and D. sacculus is the shape of the large hypothecal plates: in D. acuminata they are shorter, more convex dorsally and often more slender posteriorly; whereas, in D. sacculus they are long and sack-like. D. acuminata also exhibits more pronounced thecal areolation and sulcal list ornamentation, but these are variable features. Since these two species rarely occur in the same area with the same importance, the possibility of misidentification is reduced (Zingone et al. 1998). Surface thecal ornamentation in this species is similar to D. sacculus (Hallegraeff & Lucas 1988).

Habitat and Locality: Populations of Dinophysis acuminata are distributed widely in temperate waters. They are most common and abundant in coastal waters of the northern Atlantic and Pacific Oceans, especially eutrophic areas (Taylor et al. 1995; Steidinger & Tangen 1996).

Remarks: D. acuminata has a history wrought with identification problems mainly attributable to the morphological variability of this species. This problem is enhanced by the many synonyms and questionable identifications that have accumulated in the literature over the years (see Zingone et al. 1998). Compounding the identification problem is the influence of feeding on lateral cell shape; cells containing food vacuoles had a rounder lateral outline than cells devoid of food vacuoles (Jacobson & Andersen 1994). Many authors consider Phalacroma to be synonymous with Dinophysis (Steidinger & Tangen 1996).

Figure 1: Morphology of a Dinoflagellate