| Dinoflagellate taxa in coastal waters often form red tides that can be harmful to marine and human lives. Substantial physiological variation among strains has been observed in many red-tide forming dinoflagellate species, both within populations and among different geographic regions; however, an analysis of the intraspecific variation of a dinoflagellate species over the course of a bloom has not been previously conducted. In this dissertation, I use physiological and genetic indicators to address temporal changes in population variability and diversity in the red-tide forming dinoflagellate, Prorocentrum micans. Populations were sampled over the course of two red tides during a two year period (1998–1999) off La Jolla, California. Exponential growth rates of 39 isolates from 10 populations were measured at three temperatures (16, 18, and 20°C). The variability within populations was high and no significant difference could be detected among populations at either bloom or between-year time scales. Three genes, the large-subunit (LSU) rDNA, the 5.8S rDNA, and the cytochrome oxidase (coxI) gene, were sequenced in 25 isolates from La Jolla and other geographic regions. These genes are uninformative at the intraspecific level in P. micans; the 5.8S rRNA and coxI genes were identical among all isolates, and the LSU rDNA showed only one substitution in 3 isolates, all from widespread geographic regions. Restriction fragment length polymorphism (RFLP) analysis of the inter transcribed spacer regions (ITS) surrounding the 5.8S rDNA resulted in three different “ITS types.” All Pacific isolates were identical, and Atlantic isolates separated into two different groups. RFLP analysis is a useful indicator of intraspecific variation in P. micans, but only for widely geographically separated isolates. Finally, randomly amplified polymorphic DNA (RAPD) analysis was conducted on 173 isolates, and forty-three haplotypes were identified. Most of the variance (∼95%) was within-populations; the remaining portion (∼5%) was between populations. The diversity of populations was high, and no significant difference could be detected either between bloom and non-bloom populations or between the two different sample years. Physiological and genetic indices agree—P. micans blooms are composed of multiple strains, and the variability of populations does not change on bloom or interannual time scales. |
