Identifying Harmful Marine Dinoflagellates

Alexandrium ostenfeldii
(Paulsen) Balech et Tangen, 1985
Plate 5, Figs. 1-6

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 large 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') (Fig. 2). Faint surface pores are numerous and unevenly distributed. Cells range in size between 40-56 Ám in length and 40-50 Ám in transdiameter width (Balech 1995; Balech & Tangen 1985; Konovalova 1993; Larsen & Moestrup 1989; Taylor et al. 1995; Steidinger & Tangen 1996).

Nomenclatural Types:
Holotype: Goniodoma ostenfeldii Paulsen, 1904: 20, fig. 2
Type Locality: Iceland
Synonyms: Goniodoma ostenfeldii Paulsen, 1904
Goniaulax tamarensis Lebour var. globosa Braarud, 1945
Goniaulax ostenfeldii (Paulsen) Paulsen, 1949
Heteraulacus ostenfeldii (Paulsen) Loeblich, 1970
Gonyaulax globosa (Braarud) Balech, 1971b
Gonyaulax trygvei Parke, 1976
Protogonyaulax globosa (Braarud) Taylor, 1979
Gessnerium ostenfeldii (Paulsen) Loeblich and Loeblich, 1979
Pyrodinium phoneus Woloszynska and Conrad, 1939
Triadinium ostenfeldii (Paulsen) Dodge, 1981

Thecal Plate Description: The plate formula for A. ostenfeldii is: Po, 4', 6'', 6c, 10s, 5''', 2''''. The apical pore complex (APC) is triangular or rectangular in shape. The apical pore plate (Po) is relatively large with a large comma-shaped foramen (Figs. 2, 4). It can be either in direct contact with the first apical plate (1') (Fig. 4a) or indirectly connected via a thin suture (thread-like process) (Fig. 4b). 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. 2, 3). The distinctive sixth precingular plate (6'') is wider than high (Figs. 2,3)(Balech 1995; Balech & Tangen 1985; Larsen & Moestrup 1989; Taylor et al. 1995).
The broad epitheca is convex-conical, while the hypotheca is hemispherical with an obliquely flattened antapex (Figs. 1, 5). The slightly excavated cingulum is equatorial and displaced in a descending fashion less than one time its width; it has narrow lists (Figs. 1,3). The sulcus is slightly depressed and inconspicuous (Balech 1995; Balech & Tangen 1985; Konovalova 1993; Larsen & 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 (Fig. 5) (Balech & Tangen 1985).

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

Ecology: 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 & Conrad 1939; Hansen et al. 1992).
This species produces temporary resting cysts (Fig. 6). Cysts are large and spherical, ranging in size from 35 to 40 Ám 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 (Mackenzie et al. 1996; Jensen & Moestrup 1997).

Toxicity: 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 paralytic shellfish poison (PSP) toxins; albeit, it is the least toxic of all the Alexandrium species tested for PSP toxins (Cembella et al. 1987; 1988). This species has been associated with shellfish poisoning in Scandinavia (Jensen & Moestrup 1997), and one report of mussel Toxicity (as Pyrodinium phoneus) has been reported from Belgium (Woloszynska & 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.

Species Comparison: A. ostenfeldii is easily misidentified as other Alexandrium species; detailed thecal plate observation is often necessary for proper identification (Balech 1995; Larsen & 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 & 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 & Tangen 1996; Taylor et al. 1995).

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 & Tangen 1985), Denmark (Moestrup & Hansen 1988), Belgium (as Pyrodinium phoneus (Woloszynska & Conrad 1939), and Spain (Fraga & Sanchez 1985). Recently, Balech (1995) collected cells of A. ostenfeldii from Alexandria Harbor, Egypt, and also from the NW Pacific Ocean, off of Washington State, U.S.A. Populations have also been observed from British Columbia and the Kamchatka Peninsula in the Pacific Ocean (Konovalova 1993; Steidinger & 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).

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

Figure 1: Morphology of a Dinoflagellate