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Alexandrium ostenfeldii (Paulsen) Balech and Tangen, 1985

Species Overview:

Alexandrium ostenfeldii is an armoured, marine, planktonic dinoflagellate. Generally, it is a cold-water coastal species found in low numbers mainly along the west coast of Europe.

Taxonomical Description:

A distinctive species, cells of A. ostenfeldii are medium-sized and nearly spherical (Fig. 1). Cells are single, but are often found in two-celled colonies. Epitheca and hypotheca equal in height (Figs. 1). This species has thin thecal plates and a characteristic large ventral pore on the first apical plate (1' ) (Figs. 2,3). Faint surface pores are numerous and unevenly distributed. Cells range in size between 40-56 µm in length and 40-50 µm in transdiameter width (Balech, 1995, Balech and Tangen, 1985, Konovalova, 1993, Larsen and Moestrup, 1989, Taylor et al., 1995, Steidinger and Tangen, 1996).

Thecal Plate Description:

The plate formula for A. ostenfeldii is: Po, 4', 6'', 6c, 10s, 5''', 2''''. The apical pore plate (Po) is relatively large with a large comma-shaped foramen (Figs. 3,7). It can be either in direct contact with the first apical plate (1') or indirectly connected via a thin suture (thread-like process) (Fig. 7). The most distinctive plate of this species is the 1' plate: a) it bears a large characteristic ventral pore; and b) a 90 degree angle is formed at the point where the ventral pore and the 4' plate come in contact (Figs. 3,4). The distinctive sixth precingular plate (6'') is wider than high (Fig. 6) (Balech, 1995, Balech and Tangen, 1985, Larsen and Moestrup, 1989, Taylor et al., 1995).

The broad epitheca is convex-conical, while the hypotheca is hemispherical with an obliquely flattened antapex (Fig. 1). The slightly excavated cingulum is equatorial and displaced in a descending fashion less than one time its width; it has narrow lists (Fig. 1,6). The sulcus is slightly depressed and inconspicuous (Balech, 1995, Balech and Tangen, 1985, Konovalova, 1993, Larsen and Moestrup, 1989, Taylor et al., 1995).

Morphology and Structure:

A. ostenfeldii is a photosynthetic species with radiating chloroplasts. The nucleus is U-shaped and equatorial (Balech and Tangen, 1985).


A. ostenfeldii reproduces asexually by binary fission. This species also has a sexual cycle with isogamous mating types; a planozygote is formed (Jensen and Moestrup, 1997).

Species Comparisons:

A. ostenfeldii is easily misidentified as other Alexandrium species; detailed thecal plate observation is often necessary for proper identification (Balech, 1995, Larsen and Moestrup, 1989).

A. ostenfeldii and A. tamarense are often confused for each other since they overlap in size and often co-occur; however, A. ostenfeldii is slightly larger and is more widely distributed (has a wider salinity range) than the latter species (Moestrup and Hansen, 1988). Other differences between these two species include: A. ostenfeldii has a much larger ventral pore on the first apical plate 1'; and the 6'' plate is wider than high, whereas the width and height of the 6'' plate in A. tamarense are equal (Balech, 1995, Hansen et al., 1992).

This species also closely resembles another Alexandrium species, A. peruvianum. Both species are large cells with distinctive large ventral pores on the 1' plate; however, morphological differences are evident in the 1' plate and the APC. Moreover, A. ostenfeldii is a larger cell and produces PSP toxins (Balech, 1995, Steidinger and Tangen, 1996, Taylor et al., 1995).


Belonging to the Alexandrium complex, this A. ostenfeldii has a long and complex taxonomic history.


A. ostenfeldii is a planktonic estuarine dinoflagellate species found in low numbers, mainly along the west coast of Europe, and recently along the southeast coast of Nova Scotia, Canada (Cembella et al., 2000). To date, no blooms have been reported (except in Belgium as Pyrodinium phoneus (Woloszynska and Conrad, 1939, Hansen et al., 1992).

This species produces temporary resting cysts. Cysts are large and spherical, ranging in size from 35 to 40 µm in diameter. Cysts are pale in color with a reddish-brown granule, and a well-defined cingular groove. The smooth and clear cell wall is covered with mucilage (Figs. 4,5) (Mackenzie et al., 1996, Jensen and Moestrup, 1997).


There has long been some doubt as to the toxic potential of this species (Balech, 1995, Hansen et al., 1992). Because A. ostenfeldii does not form monospecific blooms, it has been difficult to determine this species' toxin producing potential. A. ostenfeldii, however, is capable of producing PSP toxins; albeit, it is the least toxic of all the Alexandrium species tested for PSP toxins (Cembella et al., 1987, Cembella et al., 1988). This species has been associated with shellfish poisoning in Scandinavia (Jensen and Moestrup, 1997), and one report of mussel toxicity (as Pyrodinium phoneus) has been reported from Belgium (Woloszynska and Conrad, 1939).

Recently, a study of aquaculture shellfish from Nova Scotia, Canada, revealed the presence of spirilides, fast-acting neurotoxins, primarily produced by western Atlantic strains of A. ostenfeldii (Cembella et al., 2000).

Hansen et al., 1992 conducted studies with a tintinnid ciliate exposed to high concentrations of A. ostenfeldii: results were erratic swimming behavior (backwards) followed by swelling and lysis of the ciliates.

Habitat and Locality:

A cold-water estuarine species, A. ostenfeldii was, until recently, believed to be confined to the western european coast: Iceland and Norway (Paulsen, 1904, Braarud, 1945, Balech and Tangen, 1985), Denmark (Moestrup and Hansen, 1988), Belgium (as Pyrodinium phoneus (Woloszynska and Conrad, 1939), and Spain (Fraga and Sanchez, 1985). Recently, Balech collected cells of A. ostenfeldii from Alexandria Harbor, Egypt, and also from the NW Pacific Ocean, off of Washington State, U.S.A. (Balech, 1995, Hansen et al., 1992). Populations have also been observed from British Columbia and the Kamchatka Peninsula in the Pacific Ocean (Konovalova, 1993, Steidinger and Tangen, 1996, Taylor et al., 1995). In the northwest Atlantic Ocean, cells have been reported from Canada: in the Gulf of St. Lawrence (Levasseur et al., 1998), and southeastern Nova Scotia (Cembella et al., 2000).

Alexandrium ostenfeldii