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).
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).
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).
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).
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).
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.