Overview

Brief Summary

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.

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Comprehensive Description

A. ostenfeldii has a rounded epitheca and hypotheca. The anterior and posterior sulcal plates are broad and the 1? plate has a large oval ventral pore located at the point of inflection of the angular right margin of the 1?.
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Source: Harmful Phytoplankton Project

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Physical Description

Morphology

Morphology and Structure

A. ostenfeldii is a photosynthetic species with radiating chloroplasts. The nucleus is U-shaped and equatorial (Fig. 5).

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Source: Smithsonian National Museum of Natural History Department of Botany

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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).

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.

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Source: Smithsonian National Museum of Natural History Department of Botany

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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 µm in length and 40-50 µm in transdiameter width.

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Source: Smithsonian National Museum of Natural History Department of Botany

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Look Alikes

Species Comparison

A. ostenfeldii is easily misidentified as other Alexandrium species; detailed thecal plate observation is often necessary for proper identification.

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. 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.

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.

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Ecology

Habitat

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, Denmark, Belgium (as Pyrodinium phoneus), and Spain. 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. In the northwest Atlantic Ocean, cells have been reported from Canada: in the Gulf of St. Lawrence, and southeastern Nova Scotia.

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Source: Smithsonian National Museum of Natural History Department of Botany

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Depth range based on 124 specimens in 1 taxon.
Water temperature and chemistry ranges based on 50 samples.

Environmental ranges
  Depth range (m): 0 - 100
  Temperature range (°C): -1.743 - 12.224
  Nitrate (umol/L): 1.134 - 6.894
  Salinity (PPS): 24.378 - 34.778
  Oxygen (ml/l): 6.447 - 9.192
  Phosphate (umol/l): 0.119 - 0.630
  Silicate (umol/l): 1.782 - 39.813

Graphical representation

Depth range (m): 0 - 100

Temperature range (°C): -1.743 - 12.224

Nitrate (umol/L): 1.134 - 6.894

Salinity (PPS): 24.378 - 34.778

Oxygen (ml/l): 6.447 - 9.192

Phosphate (umol/l): 0.119 - 0.630

Silicate (umol/l): 1.782 - 39.813
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

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General Ecology

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. To date, no blooms have been reported (except in Belgium as Pyrodinium phoneus).

This species produces temporary resting cysts (Fig. 6). 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.

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Life History and Behavior

Reproduction

A. ostenfeldii reproduces asexually by binary fission. This species also has a sexual cycle with isogamous mating types; a planozygote is formed.

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Physiology and Cell Biology

Physiology

Toxicity

There has long been some doubt as to the toxic potential of this species. 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. This species has been associated with shellfish poisoning in Scandinavia, and one report of mussel Toxicity (as Pyrodinium phoneus) has been reported from Belgium.

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.

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.

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Source: Smithsonian National Museum of Natural History Department of Botany

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Conservation

Management

Toxicity

A. ostenfeldii is a producer of PSP toxins and also produces spirolides (macrocyclic imine, a neurotoxin).
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Source: Harmful Phytoplankton Project

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