Figure 1. Living Pyrodinium unicells. Photo courtesy of Florida Fish and Wildlife Conservation Commission.
Figure 2a-c. Variability in Pyrodinium from Puerto Rico. Modified from Balech 1985.
Figure 3. Plate formula of Pyrodinium epitheca. Note pore on fourth apical plate (4’).
Figure 4. Pyrodinium epitheca (SEM). Arrow indicates pore on 4’.
Figure 5a. Pyrodinium APC with granular cover plate. Note pore on 4’. Detail of Figure 4.
Figure 5b. Pyrodinium APC with cover plate removed (SEM). Arrow indicates attachment pore.
Figure 6. Oblique ventral hypotheca of partially plasmolyzed Pyrodinium cell with reduced antapical spines, similar to Figure 2b. (SEM)
Figure 7. Oblique ventral view of Pyrodinium epitheca (SEM). Arrow indicates pore on 4’ plate.
Figure 8. Four cell chain of Pyrodinium (SEM). Arrow indicates apical horn.
Figure 9. Detail of Figure 8 to show prominent lists of the cingulum and crests at each plate suture.
Figure 10. Hypnocyst of Pyrodinium. Cell contents slightly plasmolyzed, brightfield light micrograph.
Figure 11. Proposed Pyrodinium life cycle. Modifed from Azanza (1997). Click to enlarge.
Pyrodinium bahamense Plate
Gonyaulax schilleri Matzenauer
Several additional species were transferred from other genera into Pyrodinium, but have subsequently been removed, leaving P. bahamense as the only species of the genus. Steidinger et al. (1980) established two varieties within the species, var. compressum and var. bahamense. There is some controversy about this distinction (see below). The names formerly included as Pyrodinium are:
P. balechii (Steidinger) Taylor [ = Alexandrium balechii (Steidinger) Balech]
P. minutum (Halim) Taylor [ = Alexandrium minutum Halim]
P. monilatum (Howell) Balech [ = Alexandrium monilatum (Howell) Balech]
P. phoneus Woloszynskia et Conrad [ = Alexandrium ostenfeldii (Paulsen) Balech et Tangen]
P. schilleri (Matzenauer) Schiller [ = P. bahamense var. compressum (Böhm) Steidinger, Tester et Taylor]
The name Pyrodinium spirale appears rarely in the literature, but little is known about the validity of this name.
The hypnocyst, dating to the Eocene epoch (34-56 million years ago) is known as Polysphaeridium zoharyi (Rossignol) Bujak et al.
According to Steidinger & Tangen (1997), Pyrodinium bahamense has the Kofoidean plate formula of APC, 4-5’, 0a, 6’’, 6c, 6s, 6’’’, 0p, 2’’’’. The APC consists of a pore plate and a cover plate (canopy). The genus is monospecific and photosynthetic. In a detailed examination, Steidinger et al. (1980) listed the ways in which the two varieties differ. The variety compressum: (1) has an apical horn, which is broader at the base, less pronounced, and usually lacks a prominent apical spine and list system; (2) is anterior-posteriorly compressed; (3) can form chains of over 30 cells; (4) usually has four apical plates - but can have, or appear to have, five as denoted by an additional thecal crest; (5) does not have the same surface markings as the variety bahamense; and (6) produces a neurotoxin. However, Balech (1995, p. 96) found that, in comparison to var. bahamense, var. compressum “is based more on the production of toxins than on morphological details”. The more recent verification of saxitoxin (see below), coupled with the variability in morphology including colony formation in var. bahamense, reduces the absolute differences between the two varieties. This suggests that they might not be separable at the variety level. To date, a thorough genetic comparison of Pacific and Atlantic strains has not appeared, though var. compressum has been examined for its genetic relationship to Alexandrium (Leaw et al. 2005).
Balech (1985) provided a thorough morphological comparison of the two varieties, and this description is based primarily on his analysis. The cells are polyhedral and irregularly rounded (Figure 1), with strong crests along the sutures (Figures 4, 5 & 9). When in chains, the cells are somewhat compressed, with width greater than height (Figure 8). The epitheca usually has a pore in the fourth apical plate (4’) (Figures 3, 4, 5a & 7). The APC consists of a comma-shaped granular closing plate and 9-14 pores (Figure 5a). There may also be an attachment pore in the APC (Figure 5b). The cingulum is displaced on the ventral side by 1.5 times or more of the width of the cingulum (Figures 5, 6 & 7). The hypotheca is approximately equal in size to the epitheca (Figure 1), and most cells have a well- developed antapical spine. There may also be smaller spine that is an extension of the sulcal list (Figures 2, 7 & 8). Both epitheca and hypotheca have numerous trichocyst pores (Figures 4, 5 & 6) and a more or less developed granular surface.
Many strains are highly bioluminescent, and blooms provide nighttime tourist attractions in Puerto Rico and Jamaica, as well as the IRL. In many natural populations, both varieties co-occur (e.g. Vargas et al. 2008), though one usually dominates over the other (see Habitat & Distribution below).
HABITAT & REGIONAL OCCURENCE:
Pyrodinium bahamense has a worldwide distribution. The variety compressum was previously believed to be toxic and confined to the Pacific Ocean, while the variety bahamense was judged nontoxic and confined to the Atlantic Ocean. Regardless of the validity of varietal distinctiveness, the species is confined to subtropical and tropical environments, either estuarine or coastal. Pacific strains are usually most abundant in salinities of 33-38 PSU (Maclean 1977; Gedaria et al. 2007), but in vitro growth occurs at lower salinities (Usup et al. 1994; Gedaria et al. 2007). The same was true for Pyrodinium in a field study in the IRL (Phlips et al. 2006).
INDIAN RIVER LAGOON DISTRIBUTION:
Although there is considerable interannual variability, Pyrodinium is normally present during most of the summer and early fall throughout the IRL, with higher abundance in the northern parts than in the southern.
The total length of cells is 47-84 µm with a width of 35-64 µm, according to Balech (1985; Jamaica and Puerto Rico specimens), and a length of 34-77 µm with a width of 34-68 µm according to Steidinger et al. (1980; Florida specimens).
GROWTH & ABUNDANCE:
Globally, Pyrodinium blooms range to a maximum of 105-106 cells per liter. The same is apparently true in the IRL, though the maximum cell density is higher in the northern IRL (Badylak & Phlips 2009) than in southern parts. The growth rate of Pyrodinium is rather low, less than 0.5 divisions per day (Gedaria et al. 2007). Therefore, high cell concentrations are probably due to some combination of low hydrodynamic activity, reduced IRL exchange with coastal water, reduced grazing rate by invertebrates, and phototactic vertical and lateral aggregation.
The life cycle of P. bahamense has been described by Azanza (1997) and appears to be typical for dinoflagellates (Figure 11). The dominant phase of the life cycle is that of haploid vegetative cells, with gametic union forming a diploid hypnozygote (hypnocyst) that undergoes meiosis after germination. The hypnocyst (Figure 10) has been found in Eocene deposits (known as Polysphaeridium zoharyi to micropaleontologists), indicating a long history for the species. These cysts are occasionally found in the IRL (Badylak & Phlips 2009), and can be induced in culture (Hargraves, pers. obs.), though the stimulus to induction is unknown. Most dinoflagellate hypnocysts require a refractory period of several months before germination, which appears to be shortened to only a few weeks for Pyrodinium (Corrales et al. 1995).
Saxitoxin is now known from both ‘varieties’, causing mortalities in a wide variety of marine organisms, in addition to human illness and/or mortality (reviewed in Landsberg 2002). Saxitoxin and its 20+ neurotoxic analogs cause paralytic shellfish poisoning (PSP) which, in the IRL, is vectored through the food web primarily through puffer fish (Abbott et al. 2009). Landsberg et al. (2006) demonstrated that saxitoxin is associated with Pyrodinium bahamense in the IRL after a series of human illnesses were traced to IRL puffer fish. While saxitoxin production is usually attributed to Pyrodinium itself, there is also evidence that the synthesis of the neurotoxin is accomplished by various genera of endosymbiotic bacteria within Pyrodinium cells (Azanza et al. 2006). According to Badylak et al. (2004), Pyrodinium in the IRL is “more closely aligned” to var. bahamense. However, var. compressum can also be found (Hargraves, pers. obs.), though not in the long chains associated with the variety.
Abbott, JP, Flewelling, LJ & JH Landsberg. 2009. Saxitoxin monitoring in three species of Florida puffer fish. Harmful Algae 8: 343-348.
Azanza, MPV, Azanza, RV, Vargas, VMD & CT Hedreyda. 2006. Bacterial endosymbionts of Pyrodinium bahamense var. compressum. Microb. Ecol. 52: 756-764.
Azanza, RV. 1997. Contribution to the understanding of the bloom dynamics of Pyrodinium bahamense var. compressum: a toxic red tide causative organism. Science Diliman 9: 1-6.
Badylak, S, Kelley, K & EJ Phlips. 2004. A description of Pyrodinium bahamense (Dinophyceae) from the Indian River Lagoon, Florida, USA. Phycologia 43: 653-657.
Badylak, S & EJ Phlips. 2009. Observations of multiple life stages of the toxic dinoflagellate Pyrodinium bahamense (Dinophyceae) in the St. Lucie estuary, Florida. Fla. Sci. 72: 208-217
Balech, E. 1985. A revision of Pyrodinium bahamense Plate (Dinoflagellata). Rev. Palaeobot. Palynol. 45: 17-34.
Balech, E. 1995. The Genus Alexandrium Halim (Dinoflagellata). Sherkin Island Marine Station, County Cork, Ireland. 151pp.
Corrales, RA, Reyes, M & M Martin. Notes on the encystment and excystment of Pyrodinium bahamense var. compressum in vitro. 573-578. In: Lassus, P et al. (Eds.). Harmful Marine Algal Blooms. Lavoisier Publishing/Springer Verlag, New York. 878pp.
Gedaria, AI, Luckas, B, Reinhardt, K & RV Azanza. 2007. Growth response and toxin concentration of cultured Pyrodinium bahamense var. compressum to varying salinity and tempersture conditions. Toxicon 50: 518-529.
Landsberg, JH. 2002. The effects of harmful algal blooms on aquatic organisms. Rev. Fish. Sci. 10: 113-390.