Alexandrium minutum

A. minutum is a planktonic dinoflagellate species associated with toxic paralytic shellfish poisoning (PSP) events in coastal regions around the world. This species also produces dense (reddish-brown) red tides (Hallegraeff 1991). A red tide of this species reported from Taiwan had cell densities of a high as 2.5 X 107 cells/L (Hwang et al. 1999). Another red tide of A. minutum reported from South Australia revealed cell levels of 4.8 X 108 cells/L (Cannon, 1990).
This species produces a clear resting cyst as part of its life cycle. Cysts vary from hemispherical to circular in shape: cyst circular in apical view (24-29 µm in diameter) (Fig. 6); kidney-shaped in lateral view (15-19 µm long). The cyst wall is covered with mucilage (Bolch et al. 1991).

A. minutum is widely distributed species found in many coastal areas of the world. Populations have been recorded from Alexandria Harbor, Egypt (Halim 1960), Italy (Montresor et al. 1990), northern Adriatic waters (Mediterranean Sea) (Honsell 1993), Turkey (Koray & Buyukisik 1988), Spain and Portugal (as A. ibericum)(Balech 1985b), France (Nezan et al. 1989), South Australia (Hallegraeff et al. 1988), and the east coast of the United States (Steidinger & Tangen 1996).

A. minutum is a photosynthetic species with an elliptical nucleus (Balech 1989; 1995).

Holotype: Alexandrium minutum Halim, 1960: 101, figs. Ia-g
Type Locality: Mediterranean Sea: Alexandria Harbor, Egypt

A. minutum reproduces asexually by binary fission. This species also has a sexual cycle that produces a characteristic resting cyst (Fig. 6)(Bolch et al. 1991).

A. minutum is an armoured, marine, planktonic dinoflagellate. It is a widely distributed species associated with toxic PSP blooms in coastal regions.

Alexandrium ibericum Balech, 1985b
Alexandrium lusitanicum Balech, 1985b

Cells of A. minutum are small, nearly spherical to ellipsoidal, somewhat dorsoventrally flattened and occassionally longer than wide (Figs. 1, 2). Cells are single with a characteristic ventral pore on the first apical plate, 1' (Figs. 1-4). Thecal plates thin. Thecal surface ornamenation can vary from light to heavy reticulation (mostly confined to the hypotheca) with small scattered pores. Intercalary bands are present (Figs. 1-3). Large range in size in this species: between 15-30 µm in length and 13-24 µm in transdiameter width (Balech 1989; 1995; Hallegraeff 1991; Taylor et al. 1995; Steidinger & Tangen 1996; Hwang et al. 1999).

The plate formula for A. minutum is: Po, 4', 6'', 6c, 10s, 5''', 2''''. The epitheca is larger than the hypotheca (Figs. 1, 2). The apical pore complex (APC) is oval to broadly triangular and pointed posteriorly (Fig. 3). The apical pore plate (Po) is large, narrow and oval with a wide comma-shaped foramen (Figs. 3, 5). The Po can be either in direct contact with the first apical plate (1') (Figs. 3,5a) or indirectly connected via a thin suture (thread-like process) (Fig. 5b). A characteristic ventral pore is located on the slender and rhomboidal 1' plate (Figs. 2-4). The distinctive sixth precingular plate (6'') long and narrow (Fig. 1) (Balech 1989; 1995; Hallegraeff 1991; Taylor et al. 1995; Steidinger & Tangen 1996; Hwang et al. 1999).
The epitheca is hemielliptical to conical with convex sides (Figs. 1, 2). The apex is broadly rounded. The short hypotheca is hemielliptical with a convex to flat antapex (Figs. 1, 2). The deeply excavated cingulum is displaced in a descending fashion one time its width with thickened margins (Figs. 1, 2). The sulcus is shallow with narrow lists (Figs. 1, 2) (Balech 1989; 1995; Hallegraeff 1991; Taylor et al. 1995; Steidinger & Tangen 1996; Hwang et al. 1999).

A. minutum is a strong producer of PSP gonyautoxins (GTX): GTX1, GTX2, GTX3 and GTX4 (Oshima et al. 1989). These toxins can affect humans, other mammals, birds and possibly fish (Hallegraeff et al. 1988; Hallegraeff 1991). This species is responsible for PSP events in Taiwan (Hwang et al. 1999), South Australia (Hallegraeff et al. 1988, Cannon 1990), France (Nezan et al. 1989) and New Zealand (Chang et al. 1995).