Over the last half of the 20th century Pyrodinium bahamense var. bahamense has been observed in a variety of locations in the western North Atlantic. Recent evidence of the toxinproducing capacity of this variety of P. bahamense has heightened interest in its habitat requirements and preferences. The objective of this study was to examine the environmental factors that relate to the spatial and temporal patterns of the distribution and abundance of P. bahamense var. bahamense. Based on the results of this study we view the factors as operating in one or more ways: (1) ecophysiological limitations for survival and successful reproductive cycle, (2) environmental regulation of growth and standing crop, and (3) competitive advantages in relation to other species. The focus of the study was the Florida peninsula, but information from other environments in the tropical Atlantic and Gulf of Mexico was included in the interpretation of the results. In terms of physiological limitations, 20°C appears to be the lower temperature limit for a significant presence of P. bahamense var. bahamense, and the salinity tolerance ranged from 10 to 45. The bloom potential of P. bahamense var. bahamense was most closely associated with shallow ecosystems with long water residence times, and peak biomass levels were correlated to nutrient concentrations in regions of high abundance. The ability of P. bahamense var. bahamense to compete effectively for habitat with other euryhaline warm-water phytoplankton is viewed in terms of existing theories on succession and competition, including Margalef's Mandala, Reynolds' Intaglio and C-S-R life-form strategies proposed by Smayda & Reynolds.

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