Identifying Harmful Marine Dinoflagellates

Gymnodinium breve
Davis, 1948
Plate 22, Figs. 1-4

Species Overview: Gymnodinium breve is an unarmoured, marine, planktonic dinoflagellate species. It is a toxin-producing species associated with red tides in the Gulf of Mexico, off the coast of western Florida.

Taxonomic Description: Gymnodinium breve is an athecate species; i.e. without thecal plates. Cells are small and dorso-ventrally flattened (Figs. 1-3). The cell is ventrally concave and dorsally convex. Cells appear almost square in outline, but with a prominent apical process directed ventrally (Figs. 1, 3, 4). Cells range in size from 20-40 Ám in width to 10-15 Ám in depth, and are slightly wider than long (Steidinger et al. 1978; Steidinger 1983; Taylor et al. 1995; Steidinger & Tangen 1996).
The epitheca is rounded with a distinctive overhanging apical process (Figs. 1-3). The epitheca is smaller than the hypotheca (Figs. 1-3). The cingulum is displaced in a descending fashion up to 2 times its width. It houses the transverse flagellum. The sulcus extends into the epitheca up to the antapex adjacent to the apical process (Fig. 4). It houses the longitudinal flagellum. An apical groove, present near the distal epithecal end of the sulcus, extends across the apical process onto the dorsal side of the cell (Figs. 1, 2). It is not an extension of the sulcus. The wide hypotheca is notched by the sulcus and is slightly bilobed posteriorly (Figs. 1-4). Discharged trichocysts have been observed (Davis 1948; Steidinger et al. 1978; Steidinger 1983; Taylor et al. 1995; Steidinger & Tangen 1996).

Nomenclatural Types:
Holotype: Gymnodinium breve Davis, 1948: 358-360, figs. 1, 2
Type Locality: Gulf of Mexico: near Naples, Florida, USA
Synonyms: Ptychodiscus brevis (Davis) Steidinger, 1979

Morphology and Structure: Gymnodinium breve is a photosynthetic species with numerous peripheral yellowish-green chloroplasts and multistalked pyrenoids (Figs. 2, 3). The large round nucleus is 6-9 Ám in diameter and located in the left half of the hypotheca (Figs. 3, 4). Lipid globules have also been observed (Fig. 3). This species does not have peridinin as a major accessory pigment (Davis 1948; Steidinger et al. 1978; Steidinger 1983; Taylor et al. 1995; Steidinger & Tangen 1996).

Reproduction: G. breve reproduces asexually by binary fission; cells divide obliquely during mitosis. This species also has a sexual cycle: isogamous gamete production, fusion and formation of a planozygote. The planozygote is morphologically similar to the vegetative cell, but larger. The gametes are rounder and slightly smaller than the vegetative cells (18-24 Ám in diameter). It is speculated that temperature controls the onset of the sexual cycle since sexual stages only occurred in fall and winter in both field populations and cultures (Walker 1982).

Ecology: G. breve is a planktonic oceanic species, though populations have been documented in estuarine systems under bloom conditions. This species is a bloom-former associated with red tides in the Gulf of Mexico, in particular the west coast of Florida. During a bloom cell levels can reach a high as 1 X 107 to 1 X 108 cells/L. Blooms initiate offshore requiring high salinities (> 30 o/oo) and high temperatures (Steidinger 1975; Steidinger et al. 1978; Steidinger & Tangen 1996). G. breve cells are active swimmers resembling 'falling leaves as they swim slowly, turning over and over through the water'. This species forms cysts under adverse conditions. Chain formation reported in very dense concentrations (Steidinger & Joyce 1973).

Toxicity: G. breve is a known toxic species that produces a series of brevetoxins (neurotoxins)(Baden 1983). These toxins are responsible for massive fill kills along the west coast of Florida in the Gulf of Mexico. Aerosolization of the toxins (noxious air-borne G. breve fragments from sea spray) has been linked to asthma-like symptoms in humans (Baden et al. 1982). Brevetoxins produce neurotoxic shellfish poisoning (NSP) when consumed (Hughes 1979). These toxins are known to cause human illness and distress; however, the poison is not fatal: no human fatalities have been reported from consumption of G. breve-infected bivalves (Steidinger & Joyce 1973). So far NSP has been restricted to the western coast of Florida, but more recently it has been documented for New Zealand as well (Steidinger et al. 1973; Baden et al. 1982; Taylor et al. 1995).

Habitat and Locality: G. breve populations are found in warm temperate to tropical waters, most regularly from the Gulf of Mexico, off the west coast of Florida. G. breve and G. breve-like species have also been reported from the West Atlantic, Spain, Greece, Japan and New Zealand (Fukuyo et al. 1990; Taylor et al. 1995; Steidinger & Tangen 1996).

Figure 1: Morphology of a Dinoflagellate

Glossary

Bibliography